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Title: Species and Varieties, Their Origin by Mutation

Author: Hugo DeVries

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Species and Varieties
Their Origin by Mutation

Lectures delivered at the University of California

By
Hugo DeVries
Professor of Botany in the University of Amsterdam

Edited by
Daniel Trembly MacDougal
Director Department of Botanical Research
Carnegie Institution of Washington

Second Edition
Corrected and Revised


CHICAGO
The Open Court Publishing Company
LONDON
Kegan Paul, Trench, Trubner and Co., Ltd.
1906

- - - - -


COPYRIGHT 1904
BY
The Open Court Pub. Co.
CHICAGO

- - - - -


THE ORIGIN OF SPECIES

The origin of species is a natural phenomenon.
LAMARCK

The origin of species is an object of inquiry.
DARWIN

The origin of species is an object of experimental investigation.
DeVRIES.

- - - - -

PREFACE BY THE AUTHOR

THE purpose of these lectures is to point out the means and methods by
which the origin of species and varieties may become an object for
experimental inquiry, in the interest of agricultural and horticultural
practice as well as in that of general biologic science. Comparative
studies have contributed all the evidence hitherto adduced for the
support of the Darwinian theory of descent and given us some general
ideas about the main lines of the pedigree of the vegetable kingdom, but
the way in which one species originates from another has not been
adequately explained. The current belief assumes that species are slowly
changed into new types. In contradiction to this conception the theory
of mutation assumes that new species and varieties are produced from
existing forms by sudden leaps. The parent-type itself remains unchanged
throughout this process, and may repeatedly give birth to new forms.
These may arise simultaneously and in groups or separately at more or
less widely distant periods.

The principal features of the theory of mutation have been dealt with at
length in my book "Die Mutationstheorie" (Vol. I., 1901, Vol. II., 1903.
Leipsic, Veit & Co.), in which I have endeavored to present as
completely as possible the detailed evidence obtained from trustworthy
historical records, and from my own experimental researches, upon which
the theory is based.

The University of California invited me to deliver a series of lectures
on this subject, at Berkeley, during the [vii] summer of 1904, and these
lectures are offered in this form to a public now thoroughly interested
in the progress of modern ideas on evolution. Some of my experiments and
pedigree-cultures are described here in a manner similar to that used in
the "Mutationstheorie," but partly abridged and partly elaborated, in
order to give a clear conception of their extent and scope. New
experiments and observations have been added, and a wider choice of the
material afforded by the more recent current literature has been made in
the interest of a clear representation of the leading ideas, leaving the
exact and detailed proofs thereof to the students of the larger book.

Scientific demonstration is often long and encumbered with difficult
points of minor importance. In these lectures I have tried to devote
attention to the more important phases of the subject and have avoided
the details of lesser interest to the general reader.

Considerable care has been bestowed upon the indication of the lacunae
in our knowledge of the subject and the methods by which they may be
filled. Many interesting observations bearing upon the little known
parts of the subject may be made with limited facilities, either in the
garden or upon the wild flora. Accuracy and perseverance, and a warm
love for Nature's children are here the chief requirements in such
investigations.

In his admirable treatise on Evolution and Adaptation (New York,
Macmillan & Co., 1903), Thomas Hunt Morgan has dealt in a critical
manner with many of the speculations upon problems subsidiary to the
theory of descent, in so convincing and complete a manner, that I think
myself justified in neglecting these questions here. His book gives an
accurate survey of them all, and is easily understood by the general
reader.

In concluding I have to offer my thanks to Dr. D.T. MacDougal and Miss
A.M. Vail of the New York Botanical Garden for their painstaking work in
the preparation of the manuscript for the press. Dr. MacDougal, by
[viii] his publications, has introduced my results to his American
colleagues, and moreover by his cultures of the mutative species of the
great evening-primrose has contributed additional proof of the validity
of my views, which will go far to obviate the difficulties, which are
still in the way of a more universal acceptation of the theory of
mutation. My work claims to be in full accord with the principles laid
down by Darwin, and to give a thorough and sharp analysis of some of the
ideas of variability, inheritance, selection, and mutation, which were
necessarily vague at his time. It is only just to state, that Darwin
established so broad a basis for scientific research upon these
subjects, that after half a century many problems of major interest
remain to be taken up. The work now demanding our attention is
manifestly that of the experimental observation and control of the
origin of species. The principal object of these lectures is to secure a
more general appreciation of this kind of work.


HUGO DE VRIES.
Amsterdam, October, 1904.

[ix]

PREFACE BY THE EDITOR

PROFESSOR DE VRIES has rendered an additional service to all naturalists
by the preparation of the lectures on mutation published in the present
volume. A perusal of the lectures will show that the subject matter of
"Die Mutationstheorie" has been presented in a somewhat condensed form,
and that the time which has elapsed since the original was prepared has
given opportunity for the acquisition of additional facts, and a
re-examination of some of the more important conclusions with the result
that a notable gain has been made in the treatment of some complicated
problems.

It is hoped that the appearance of this English version of the theory of
mutation will do much to stimulate investigation of the various phases
of the subject. This volume, however, is by no means intended to
replace, as a work of reference, the larger book with its detailed
recital of facts and its comprehensive records, but it may prove a
substitute for the use of the general reader.

The revision of the lectures has been a task attended with no little
pleasure, especially since it has given the editor the opportunity for
an advance consideration of some of the more recent results, thus
materially facilitating investigations which have been in progress at
the New York Botanical Garden for some time. So far as the ground has
been covered the researches in question corroborate the conclusions of
de Vries in all important particulars. The preparation of the manuscript
for the printer has consisted chiefly in the adaptation of oral [xii]
discussions and demonstrations to a form suitable for permanent record,
together with certain other alterations which have been duly submitted
to the author. The original phraseology has been preserved as far as
possible. The editor wishes to acknowledge material assistance in this
work from Miss A.M. Vail, Librarian of the New York Botanical Garden.


D.T. MacDougal.
New York Botanical Garden, October, 1904.


PREFACE TO THE SECOND EDITION.

THE constantly increasing interest in all phases of evolution has made
necessary the preparation of a second edition of this book within a few
months after the first appeared. The opportunity has been used to
eliminate typographical errors, and to make alterations in the form of a
few sentences for the sake of clearness and smoothness. The subject
matter remains practically unchanged. An explanatory note has been added
on page 575 in order to avoid confusion as to the identity of some of
the plants which figure prominently in the experimental investigations
in Amsterdam and New York.

The portrait which forms the frontispiece is a reproduction of a
photograph taken by Professor F.E. Lloyd and Dr. W.A. Cannon during the
visit of Professor de Vries at the Desert Botanical Laboratory of the
Carnegie Institution, at Tucson, Arizona, in June, 1904.


D. T. MACDOUGAL.
December 15, 1905.



CONTENTS

A. INTRODUCTION.

LECTURE                                                            PAGE

I. Descent: theories of evolution and methods of investigation.       1
     The theory of descent and of natural selection. Evolution and
adaptation. Elementary species and varieties. Methods of scientific
pedigree-culture.

B. ELEMENTARY SPECIES.

II. Elementary species in nature.                                    32
     _Viola tricolor_, _Draba verna_, _Primula acaulis_, and other
examples. _Euphorbia pecacuanha_. _Prunus maritima_. _Taraxacum_ and
_Hieracium_.

III. Elementary species of cultivated plants.                        63
     Beets, apples, pears, clover, flax and coconut.

IV. Selection of elementary species.                                 92
     Cereals. Le Couteur. Running out of varieties. Rimpau and
Risler, _Avena fatua_. Meadows. Old Egyptian cereals. Selection by the
Romans. Shirreff. Hays.

C. RETROGRADE VARIETIES.

V. Characters of retrograde varieties.                              121
     Seed varieties of pure, not hybrid origin. Differences from
elementary species. Latent characters. Ray-florets of composites.
[xiii] Progressive red varieties. Apparent losses. _Xanthium
canadense_. Correlative variability. Laciniate leaves and petals.
Compound characters.

VI. Stability and real atavism.                                     154
     Constancy of retrograde varieties. Atavism in _Ribes sanguineum
Albidum_, in conifers, in _Iris pallida_. Seedlings of _Acacia_.
Reversion by buds.

VII. Ordinary or false atavism.                                     185
     Vicinism or variation under the influence of pollination by
neighboring individuals. Vicinism in nurseries. Purifying new and
old varieties. A case of running out of corn in Germany.

VIII. Latent characters.                                            216
     Leaves of seedlings, adventitious buds, systematic latency and
retrogressive evolution. Degressive evolution. Latency of specific
and varietal characters in wheat-ear carnation, in the green dahlias,
in white campanulas and others. Systematic latency of flower colors.

IX. Crossing of species and varieties.                              247
     Balanced and unbalanced, or species and variety crosses.
Constant hybrids of _Oenothera muricata_ and _O. biennis_. _Aegilops_,
_Medicago_, brambles and other instances.

X. Mendel's law of balanced crosses.                                276
     Pairs of antagonistic characters, one active and one latent.
_Papaver somniferum_. [xiv] _Mephisto Danebrog_. Mendel's laws. Unit-
characters.

D. EVERSPORTING VARIETIES.

XI. Striped flowers.                                                309
     _Antirrhinum majus luteum rubro-striatum_ with pedigree. Striped
flowers, fruits and radishes. Double stocks.

XII. "Five leaved" clover.                                          340
     Origin of this variety. Periodicity of the anomaly. Pedigree-
cultures. Ascidia.

XIII. Polycephalic poppies.                                         369
     Permanency and high variability. Sensitive period of the
anomaly. Dependency on external conditions.

XIV. Monstrosities.                                                 400
     Inheritance of monstrosities. Half races and middle races.
Hereditary value of atavists. Twisted stems and fasciations. Middle
races of tricotyls and syncotyls. Selection by the hereditary
percentage among the offspring.

XV. Double adaptations.                                             430
     Analogy between double adaptations and anomalous middle races.
_Polygonum amphibium_. Alpine plants. _Othonna crassifolia_. Leaves
in sunshine and shadow. Giants and dwarfs. Figs and ivy. Leaves of
seedlings.

E. MUTATIONS.

XVI. Origin of the peloric toad-flax.                               459
     Sudden and frequent origin in the wild state. Origin in the
experiment-garden. Law of repeated mutations. Probable origin of
other pelories.

[xv]
XVII.  The production of double flowers.                            488
     Sudden appearance of double flowers in horticulture. Historical
evidence. Experimental origin of _Chrysanthemum segetum plenum_.
Dependency upon nourishment. Petalody of stamens.

XVIII New species of _Oenothera_.                                   516
     Mutations of _Oenothera lamarckiana_ in the wild state near
Hilversum. New varieties of _O. laevifolia_, _O. brevistylis_, and
_O. nanella_. New elementary species, _O. gigas_, _O. rubrinervis_,
_albida_, and _oblonga_. _O. lata_, a pistillate form.
Inconstancy of _O. scintillans_.

XIX. Experimental pedigree-cultures.                                547
     Pedigree of the mutative products of _Oenothera lamarckiana_ in
the Botanical Garden at Amsterdam. Laws of mutability. Sudden and
repeated leaps from an unchanging main strain. Constancy of the new
forms. Mutations in all directions.

XX. Origin of wild species and varieties.                           576
     Problems to solve. _Capsella heegeri_. _Oenothera biennis cruciata_.
_Epilobium hirsutum cruciatum_. _Hibiscus Moscheutos_. Purple beech.
Monophyllous strawberries. Chances of success with new mutations.

XXI. Mutations in horticulture.                                     604
     _Chelidonium majus lacinatum_. Dwarf and spineless varieties.
Laciniate leaves. Monophyllous and broom-like varieties. [xvi] Purple
leaves. _Celosia_. Italian poplar. Cactus dahlia. Mutative origin of
_Dahlia fistulosa_, and _Geranium praetense_ in the experiment-garden.

XXII. Systematic atavism.                                           630
Reappearance of ancestral characters. _Primula acaulis umbellata_.
Bracts of crucifers. _Zea Mays cryptosperma_. Equisetum, _Dipsacus
sylvestris torsus_. Tomatoes.

XXIII. Taxonomic anomalies.                                         658
     Specific characters occurring in other cases as casual
anomalies. _Papaver bracteatum monopetalum_. _Desmodium gyrans_ and
monophyllous varieties. Peltate leaves and ascidia. Flowers on
leaves. Leaves. _Hordeum trifurcatum_.

XXIV. Hypothesis of periodical mutations.                           686
     Discovering mutable strains. Periods of mutability and constancy.
Periods of mutations. Genealogical trees. Limited life-time of the
organic kingdom.


F. FLUCTUATIONS.

XXV. General laws of fluctuations.                                  715
     Fluctuating variability. Quetelet's law. Individual and partial
fluctuations. Linear variability. Influence of nutrition.
Periodicity curves.

XXVI. Asexual multiplication of extremes.                           742
     Selection between species and intra-specific selection.
Excluding individual [xvii] embryonic variability. Sugar-canes.
Flowering cannas. Double lilacs. Other instances. Burbank's method
of selection.

XXVII. Inconstancy of improved races                                770
     Larger variability in the case of propagation by seed,
progression and regression after a single selection, and after
repeated selections. Selection experiments with corn. Advantages
and effect of repeated selection.

XXVIII. Artificial and natural selection.                           798
     Conclusions. Specific and intra-specific selection. Natural
selection in the field. Acclimatization. Improvement-selection of
sugar-beets by various methods. Rye. Hereditary percentage and
centgener power as marks by which intraspecific selection may be
guided.

Index                                                               827


[1]
A. INTRODUCTION

LECTURE I

DESCENT: THEORIES OF EVOLUTION
AND METHODS OF INVESTIGATION

Newton convinced his contemporaries that natural laws rule the whole
universe. Lyell showed, by his principle of slow and gradual evolution,
that natural laws have reigned since the beginning of time. To Darwin we
owe the almost universal acceptance of the theory of descent.

This doctrine is one of the most noted landmarks in the advance of
science. It teaches the validity of natural laws of life in its broadest
sense, and crowns the philosophy founded by Newton and Lyell.

Lamarck proposed the hypothesis of a common origin of all living beings
and this ingenious and thoroughly philosophical conception was warmly
welcomed by his partisans, but was not widely accepted owing to lack of
supporting evidence. To Darwin was reserved the task of [2] bringing the
theory of common descent to its present high rank in scientific and
social philosophy.

Two main features in his work have contributed to this early and
unexpected victory. One of them is the almost unlimited amount of
comparative evidence, the other is his demonstration of the possibility
of a physiological explanation of the process of descent itself.

The universal belief in the independent creation of living organisms was
revised by Linnaeus and was put upon a new foundation. Before him the
genera were supposed to be created, the species and minor forms having
arisen from them through the agency of external conditions. In his first
book Linnaeus adhered to this belief, but later changed his mind and
maintained the principle of the separate creation of species. The weight
of his authority soon brought this conception to universal acceptance,
and up to the present time the prevailing conception of a species has
been chiefly based on the definition given by Linnaeus. His species
comprised subspecies and varieties, which were in their turn, supposed
to have evolved from species by the common method.

Darwin tried to show that the links which bind species to genera are of
the same nature as those which determine the relationship of [3]
subspecies and varieties. If an origin by natural laws is conceded for
the latter, it must on this ground be granted for the first also. In
this discussion he simply returned to the pre-Linnean attitude. But his
material was such as to allow him to go one step further, and this step
was an important and decisive one. He showed that the relation between
the various genera of a family does not exhibit any features of a nature
other than that between the species of a genus. What has been conceded
for the one must needs be accepted for the other. The same holds good
for the large groups.

The conviction of the common origin of closely allied forms necessarily
leads to the conception of a similar descent even in remote
relationships.

The origin of subspecies and varieties as found in nature was not
proved, but only generally recognized as evident. A broader knowledge
has brought about the same state of opinion for greater groups of
relationships. Systematic affinities find their one possible explanation
by the aid of this principle; without it, all similarity is only
apparent and accidental. Geographic and paleontologic facts, brought
together by Darwin and others on a previously unequalled scale, point
clearly in the same direction. The vast amount of evidence of all [4]
comparative sciences compels us to accept the idea. To deny it, is to
give up all opportunity of conceiving Nature in her true form.

The general features of the theory of descent are now accepted as the
basis of all biological science. Half a century of discussion and
investigation has cleared up the minor points and brought out an
abundance of facts; but they have not changed the principle. Descent
with modification is now universally accepted as the chief law of nature
in the organic world. In honor of him, who with unsurpassed genius, and
by unlimited labor has made it the basis of modern thought, this law is
called the "Darwinian theory of descent."

Darwin's second contribution to this attainment was his proof of the
possibility of a physiological explanation of the process of descent
itself. Of this possibility he fully convinced his contemporaries, but
in indicating the particular means by which the change of species has
been brought about, he has not succeeded in securing universal
acceptation. Quite on the contrary, objections have been raised from the
very outset, and with such force as to compel Darwin himself to change
his views in his later writings. This however, was of no avail, and
objections and criticisms have since steadily accumulated. Physiologic
facts concerning the origin of [5] species in nature were unknown in the
time of Darwin. It was a happy idea to choose the experience of the
breeders in the production of new varieties, as a basis on which to
build an explanation of the processes of nature. In my opinion Darwin
was quite right, and he has succeeded in giving the desired proof. But
the basis was a frail one, and would not stand too close an examination.
Of this Darwin was always well aware. He has been prudent to the utmost,
leaving many points undecided, and among them especially the range of
validity of his several arguments. Unfortunately this prudence has not
been adopted by his followers. Without sufficient warrant they have laid
stress on one phase of the problem, quite overlooking the others.
Wallace has even gone so far in his zeal and ardent veneration for
Darwin, as to describe as Darwinism some things, which in my opinion,
had never been a part of Darwin's conceptions.

The experience of the breeders was quite inadequate to the use which
Darwin made of it. It was neither scientific, nor critically accurate.
Laws of variation were barely conjectured; the different types of
variability were only imperfectly distinguished. The breeders'
conception was fairly sufficient for practical purposes, but science
needed a clear understanding of the [6] factors in the general process
of variation. Repeatedly Darwin tried to formulate these causes, but the
evidence available did not meet his requirements.

Quetelet's law of variation had not yet been published. Mendel's claim
of hereditary units for the explanation of certain laws of hybrids
discovered by him, was not yet made. The clear distinction between
spontaneous and sudden changes, as compared with the ever-present
fluctuating variations, is only of late coming into recognition by
agriculturists. Innumerable minor points which go to elucidate the
breeders' experience, and with which we are now quite familiar, were
unknown in Darwin's time. No wonder that he made mistakes, and laid
stress on modes of descent, which have since been proved to be of minor
importance or even of doubtful validity.

Notwithstanding all these apparently unsurmountable difficulties, Darwin
discovered the great principle which rules the evolution of organisms.
It is the principle of natural selection. It is the sifting out of all
organisms of minor worth through the struggle for life. It is only a
sieve, and not a force of nature, not a direct cause of improvement, as
many of Darwin's adversaries, and unfortunately many of his followers
also, have so often asserted.

It is [7] only a sieve, which decides what is to live, and what is to
die. But evolutionary lines are of great length, and the evolution of a
flower, or of an insectivorous plant is a way with many sidepaths. It is
the sieve that keeps evolution on the main line, killing all, or nearly
all that try to go in other directions. By this means natural selection
is the one directing cause of the broad lines of evolution.

Of course, with the single steps of evolution it has nothing to do. Only
after the step has been taken, the sieve acts, eliminating the unfit.
The problem, as to the manner in which the individual steps are brought
about, is quite another side of the question.

On this point Darwin has recognized two possibilities. One means of
change lies in the sudden and spontaneous production of new forms from
the old stock. The other method is the gradual accumulation of those
always present and ever fluctuating variations which are indicated by
the common assertion that no two individuals of a given race are exactly
alike. The first changes are what we now call "mutations," the second
are designated as "individual variations," or as this term is often used
in another sense, as "fluctuations." Darwin recognized both lines of
evolution; Wallace disregarded the sudden changes and proposed
fluctuations [8] as the exclusive factor. Of late, however, this point
of view has been abandoned by many investigators, especially in America.

The actual occurrence of mutations is recognized, and the battle rages
about the question, as to whether they are be regarded as the principal
means of evolution, or whether slow and gradual changes have not also
played a large and important part.

The defenders of the theory of evolution by slow accumulation of slight
fluctuations are divided into two camps. One group is called the
Neo-Lamarckians; they assume a direct modifying agency of the
environment, producing a corresponding and useful change in the
organization. The other group call themselves Darwinians or
selectionists, but to my mind with no other right beyond the arbitrary
restriction of the Darwinian principles by Wallace. They assume
fluctuating variations in all directions and leave the choice between
them to the sieve of natural selection.

Of course we are far from a decision between these views, on the sole
ground of the facts as known at present. Mutations under observation are
as yet very rare; enough to indicate the possible and most probable
ways, but no more. On the other hand the accumulation of fluctuations
does not transgress relatively narrow [9] limits as far as the present
methods of selection go. But the question remains to be solved, whether
our methods are truly the right ones, and whether by the use of new
principles, new results might not cause the balance of opinion to favor
the opposite side.

Of late, a thorough and detailed discussion of the opposing views has
been given by Morgan in his valuable book on evolution and adaptation.
He has subjected all the proposed theories to a severe criticism both on
the ground of facts and on that of their innate possibility and logical
value. He decides in favor of the mutation theory. His arguments are
incisive and complete and wholly adapted to the comprehension of all
intelligent readers, so that his book relieves me entirely of the
necessity of discussing these general questions, as it could not be done
in a better or in a clearer way.

I intend to give a review of the facts obtained from plants which go to
prove the assertion, that species and varieties have originated by
mutation, and are, at present, not known to originate in any other way.
This review consists of two parts. One is a critical survey of the facts
of agricultural and horticultural breeding, as they have accumulated
since the time of Darwin. This body of evidence is to be combined with
some corresponding experiments [10] concerning the real nature of
species in the wild state. The other part rests on my own observations
and experiments, made in the botanical garden of the University of
Amsterdam.

For many years past I have tried to elucidate the hereditary conditions
of species and varieties, and the occasional occurrence of mutations,
that suddenly produce new forms.

The present discussion has a double purpose. On one side it will give
the justification of the theory of mutations, as derived from the facts
now at hand. On the other hand it will point out the deficiencies of
available evidence, and indicate the ways by which the lacunae may
gradually be filled. Experimental work on heredity does not require vast
installments or costly laboratory equipment. It demands chiefly
assiduity and exactitude. Any one who has these two qualities, and who
has a small garden at his disposal is requested to take part in this
line of investigation.

In order to observe directly the birth of new forms it is necessary, in
the first place, to be fully clear concerning the question as to what
forms are to be expected to arise from others, and before proceeding to
a demonstration of the origin of species, it is pertinent to raise the
question as to what constitutes a species.

Species is a word, which always has had a [11] double meaning. One is
the systematic species, which is the unit of our system. But these units
are by no means indivisible. Long ago Linnaeus knew them to be compound
in a great number of instances, and increasing knowledge has shown that
the same rule prevails in other instances. Today the vast majority of
the old systematic species are known to consist of minor units. These
minor entities are called varieties in systematic works. However, there
are many objections to this usage. First, the term variety is applied in
horticulture and agriculture to things so widely divergent as to convey
no clear idea at all. Secondly, the subdivisions of species are by no
means all of the same nature, and the systematic varieties include units
the real value of which is widely different in different cases. Some of
these varieties are in reality as good as species, and have been
"elevated," as it is called by some writers, to this rank. This
conception of the elementary species would be quite justifiable, and
would at once get rid of all difficulties, were it not for one practical
obstacle. The number of the species in all genera would be doubled and
tripled, and as these numbers are already cumbersome in many cases, the
distinction of the native species of any given country would lose most
of its charm and interest.

[12] In order to meet this difficulty we must recognize two sorts of
species. The systematic species are the practical units of the
systematists and florists, and all friends of wild nature should do
their utmost to preserve them as Linnaeus has proposed them. These units
however, are not really existing entities; they have as little claim to
be regarded as such as genera and families. The real units are the
elementary species; their limits often apparently overlap and can only
in rare cases be determined on the sole ground of field observations.
Pedigree-culture is the method required and any form which remains
constant and distinct from its allies in the garden is to be considered
as an elementary species.

In the following lectures we shall consider this point at length, to
show the compound nature of systematic species in wild and in cultivated
plants. In both cases, the principle is becoming of great importance,
and many papers published recently indicate its almost universal
acceptation.

Among the systematic subdivisions of species, not all have the same
claim to the title of elementary species. In the first place the cases
in which the differences may occur between parts of the same individual
are to be excluded. Dividing an alpine plant into two halves and [13]
planting one in a garden, varietal differences at once arise and are
often designated in systematic works under different varietal names.
Secondly all individual differences which are of a fluctuating nature
are to be combined into a group. But with these we shall deal later.

Apart from these minor points the subdivisions of the systematic species
exhibit two widely different features. I will now try to make this clear
in a few words, but will return in another lecture to a fuller
discussion of this most interesting contrast.

Linnaeus himself knew that in some cases all subdivisions of a species
are of equal rank, together constituting the group called species. No
one of them outranks the others; it is not a species with varieties, but
a group, consisting only of varieties. A closer inquiry into the cases
treated in this manner by the great master of systematic science, shows
that here his varieties were exactly what we now call elementary
species.

In other cases the varieties are of a derivative nature. The species
constitutes a type that is pure in a race which ordinarily is still
growing somewhere, though in some cases it may have died out. From this
type the varieties are derived, and the way of this derivation is
usually quite manifest to the botanist. It is ordinarily [14] by the
disappearance of some superficial character that a variety is
distinguished from its species, as by the lack of color in the flowers,
of hairs on stems and foliage, of the spines and thorns, &c. Such
varieties are, strictly speaking, not to be treated in the same way as
elementary species, though they often are. We shall designate them by
the term of "retrograde varieties," which clearly indicates the nature
of their relationship to the species from which they are assumed to have
sprung. In order to lay more stress on the contrast between elementary
species and retrograde varieties, it should be stated at once, that the
first are considered to have originated from their parent-form in a
progressive way. They have succeeded in attaining something quite new
for themselves, while retrograde varieties have only thrown off some
peculiarity, previously acquired by their ancestors.

The whole vegetable kingdom exhibits a constant struggle between
progression and retrogression. Of course, the great lines of the general
pedigree are due to progression, many single steps in this direction
leading together to the great superiority of the flowering plants over
their cryptogamous ancestors. But progression is nearly always
accompanied by retrogression in the principal lines of evolution, [15]
as well as in the collateral branches of the genealogical tree.
Sometimes it prevails, and the monocotyledons are obviously a reduced
branch of the primitive dicotyledons. In orchids and aroids, in grasses
and sedges, reduction plays a most important part, leaving its traces on
the flowers as well as on the embryo of the seed. Many instances could
be given to prove that progression and retrogression are the two main
principles of evolution at large. Hence the conclusion, that our
analysis must dissect the complicated phenomena of evolution so far as
to show the separate functions of these two contrasting principles.
Hundreds of steps were needed to evolve the family of the orchids, but
the experimenter must take the single steps for the object of his
inquiry. He finds that some are progressive and others retrogressive and
so his investigation falls under two heads, the origin of progressive
characters, and the subsequent loss of the same. Progressive steps are
the marks of elementary species, while retrograde varieties are
distinguished by apparent losses. They have equal claim to our interest
and our study.

As already stated I propose to deal first with the elementary species
and afterwards with the retrograde varieties. I shall try to depict them
to you in the first place as they are seen in [16] nature and in
culture, leaving the question of their origin to a subsequent
experimental treatment.

The question of the experimental origin of new species and varieties has
to be taken up from two widely separated starting points. This may be
inferred from what we have already seen concerning the two opposing
theories, derived and isolated from Darwin's original broad conception.
One of them considers mutations as the origin of new forms, while the
other assumes fluctuations to be the source of all evolution.

As mentioned above, my own experience has led me to accept the first
view. Therefore I shall have to show that mutations do yield new and
constant forms, while fluctuations are not adequate to do so. Retrograde
varieties and elementary species may both be seen to be produced by
sudden mutations. Varieties have often been observed to appear at once
and quite unexpectedly in horticulture and agriculture, and a survey of
these historical facts will be the subject of one of my lectures. In
some instances I have succeeded in repeating these observations in my
garden under the strict conditions of a scientific experiment, and these
instances teach us the real nature of the process of mutation in all its
visible features. New elementary [17] species are far more rare, but I
have discovered in the great evening-primrose, or _Oenothera
lamarckiana_ a strain which is producing them yearly in the wild state
as well as in my garden. These observations and pedigree-experiments
will be dealt with at due length in subsequent lectures.

Having proved the existence and importance of mutations, it remains to
inquire how far the improvements may go which are due only to
fluctuating variability. As the term indicates, this variability is
fluctuating to and fro, oscillating around an average type. It never
fails nor does it, under ordinary circumstances, depart far from the
fixed average.

But the deviation may be enlarged by a choice of extremes. In sowing
their seed, the average of the strain is seen to be changed, and in
repeating the experiment the change may be considerable. It is not
clear, whether theoretically by such an accumulation, deviations might
be reached which could not be attained at once in a single sowing. This
question is hardly susceptible of an experimental answer, as it would
require such an enormous amount of seed from a few mother plants as can
scarcely ever be produced.

The whole character of the fluctuations shows them to be of an opposite
nature, contrasting [18] manifestly with specific and varietal
characters. By this method they may be proved to be inadequate ever to
make a single step along the great lines of evolution, in regard to
progressive as well as to retrograde development.

First of all fluctuations are linear, amplifying or lessening the
existing qualities, but not really changing their nature. They are not
observed to produce anything quite new, and evolution of course, is not
restricted to the increase of the already existing peculiarities, but
depends chiefly on the continuous addition of new characters to the
stock. Fluctuations always oscillate around an average, and if removed
from this for some time, they show a tendency to return to it. This
tendency, called retrogression, has never been observed to fail, as it
should, in order to free the new strain from the links with the average,
while new species and new varieties are seen to be quite free from their
ancestors and not linked to them by intermediates.

The last few lectures will be devoted to questions concerning the great
problem of the analogy between natural and artificial selection. As
already stated, Darwin made this analogy the foundation stone of his
theory of descent, and he met with the severest objections and
criticisms precisely on this point. But I hope to [19] show that he was
quite right, and that the cause of the divergence of opinions is due
simply to the very incomplete state of knowledge concerning both
processes. If both are critically analyzed they may be seen to comprise
the same factors, and further discussion may be limited to the
appreciation of the part which each of them has played in nature and
among cultivated plants.

Both natural and artificial selection are partly specific, and partly
intra-specific or individual. Nature of course, and intelligent men
first chose the best elementary species from among the swarms. In
cultivation this is the process of variety-testing. In nature it is the
survival of the fittest species, or, as Morgan designates it, the
survival of species in the struggle for existence. The species are not
changed by this struggle, they are only weighed against each other, the
weak being thrown aside.

Within the chosen elementary species there is also a struggle. It is
obvious, that the fluctuating variability adapts some to the given
circumstances, while it lessens the chances of others. A choice results,
and this choice is what is often exclusively called selection, either
natural or artificial. In cultivation it produces the improved and the
local races; in nature little is known about improvement in this way,
but [19] local adaptations with slight changes of the average character
in separate localities, seem to be of quite normal occurrence.

A new method of individual selection has been used in recent years in
America, especially by W.M. Hays. It consists in judging the hereditary
worth of a plant by the average condition of its offspring, instead of
by its own visible characters. If this determination of the "centgener
power," as Hays calls it, should prove to be the true principle of
selection, then indeed the analogy between natural and artificial
selection would lose a large part of its importance. We will reserve
this question for the last lecture, as it pertains more to the future,
than to our present stock of knowledge.

Something should be said here concerning hybrids and hybridism. This
problem has of late reached such large proportions that it cannot be
dealt with adequately in a short survey of the phenomena of heredity in
general. It requires a separate treatment. For this reason I shall limit
myself to a single phase of the problem, which seems to be indispensable
for a true and at the same time easy distinction between elementary
species and retrograde varieties. According to accepted terminology,
some crosses are to be considered as unsymmetrical, while others are
symmetrical. The first are one-sided, [21] some peculiarity being found
in one of the parents and lacking in the other. The second are balanced,
as all the characters are present in both parents, but are found in a
different condition. Active in one of them, they are concealed or
inactive in the other. Hence pairs of contrasting units result, while in
unbalanced crosses no pairing of the particular character under
consideration is possible. This leads to the principal difference
between species and varieties, and to an experimental method of deciding
between them in difficult and doubtful cases.

Having thus indicated the general outlines of the subjects I shall deal
with, something now may be said as to methods of investigation.

There are two points in which scientific investigation differs from
ordinary pedigree-culture in practice. First the isolation of the
individuals and the study of individual inheritance, instead of
averages. Next comes the task of keeping records. Every individual must
be entered, its ancestry must be known as completely as possible, and
all its relations must be noted in such a form, that the most complete
reference is always possible. Mutations may come unexpectedly, and when
once arisen, their parents and grand-parents should be known. Records
must be available which will allow of a most complete knowledge of the
whole ancestral [22] line. This, and approximately this only, is the
essential difference between experimental and accidental observation.

Mutations are occurring from time to time in the wild state as well as
in horticulture and agriculture. A selection of the most interesting
instances will be given later. But in all such cases the experimental
proof is wanting. The observations as a rule, only began when the
mutation had made its appearance. A more or less vague remembrance about
the previous state of the plants in question might be available, though
even this is generally absent. But on doubtful points, concerning
possible crosses or possible introduction of foreign strains, mere
recollection is insufficient. The fact of the mutation may be very
probable, but the full proof is, of course, wanting. Such is the case
with the mutative origin of _Xanthium commune_ Wootoni from New Mexico
and of _Oenothera biennis cruciata_ from Holland. The same doubt exists
as to the origin of the _Capsella heegeri_ of Solms-Laubach, and of the
oldest recorded mutation, that of _Chelidonium laciniatum_ in Heidelberg
about 1600.

First, we have doubts about the fact itself. These, however, gradually
lose their importance in the increasing accumulation of evidence.
Secondly, the impossibility of a closer [23] inquiry into the real
nature of the change. For experimental purposes a single mutation does
not suffice; it must be studied repeatedly, and be produced more or less
arbitrarily, according to the nature of the problems to be solved. And
in order to do this, it is evidently not enough to have in hand the
mutated individual, but it is indispensable to have also the mutable
parents, or the mutable strain from which it sprang.

All conditions previous to the mutation are to be considered as of far
higher importance than all those subsequent to it.

Now mutations come unexpectedly, and if the ancestry of an accidental
mutation is to be known, it is of course necessary to keep accounts of
all the strains cultivated. It is evident that the required knowledge
concerning the ancestry of a supposed mutation, must necessarily nearly
all be acquired from the plants in the experimental garden.

Obviously this rule is as simple in theory, as it is difficult to carry
out in practice. First of all comes the book-keeping. The parents,
grandparents and previous ancestors must be known individually. Accounts
of them must be kept under two headings. A full description of their
individual character and peculiarities must always be available on the
one hand, and on the other, all facts concerning their hereditary [24]
qualities. These are to be deduced from the composition of the progeny,
and in order to obtain complete evidence on this point, two successive
generations are often required. The investigation must ascertain the
average condition of this offspring and the occurrence of any deviating
specimens, and for both purposes it is necessary to cultivate them in
relatively large numbers. It is obvious that, properly speaking, the
whole family of a mutated individual, including all its nearer and more
remote relatives, should be known and recorded.

Hence pedigree-book-keeping must become the general rule. Subordinate to
this are two further points, which should likewise be stated here. One
pertains to the pure or hybrid nature of the original strain, and the
other to the life-conditions and all other external influences. It is
manifest that a complete understanding of a mutation depends upon full
information upon these points.

All experiments must have a beginning. The starting-point may be a
single individual, or a small group of plants, or a lot of seeds. In
many cases the whole previous history is obscure, but sometimes a little
historical evidence is at hand. Often it is evident that the initial
material belongs to a pure species, but with respect to the question of
elementary species it is [25] not rarely open to doubt. Large numbers of
hybrid plants and hybrid races are in existence, concerning the origin
of which it is impossible to decide. It is impossible in many instances
to ascertain whether they are of hybrid or of pure origin. Often there
is only one way of determining the matter; it is to guess at the
probable parents in case of a cross and to repeat the cross. This is a
point which always requires great care in the interpretation of unusual
facts.

Three cases are to be distinguished as to heredity. Many plants are so
constituted as to be fertilized with their own pollen. In this case the
visits of insects have simply to be excluded, which may be done by
covering plants with iron gauze or with bags of prepared paper.
Sometimes they fertilize themselves without any aid, as for instance,
the common evening-primrose; in other cases the pollen has to be placed
on the stigma artificially, as with Lamarck's evening-primrose and its
derivatives. Other plants need cross-fertilization in order to produce a
normal yield of seeds. Here two individuals have always to be combined,
and the pedigree becomes a more complicated one. Such is the case with
the toad-flax, which is nearly sterile with its own pollen. But even in
these cases the visits of insects bringing pollen [26] from other
plants, must be carefully excluded. A special lecture will be devoted to
this very interesting source of impurity and of uncertainty in ordinary
cultures.

Of course, crosses may lie in the proposed line of work, and this is the
third point to be alluded to. They must be surrounded with the same
careful isolation and protection against bees, as any other
fertilizations. And not only the seed-parent, but also the pollen must
be kept pure from all possible foreign admixtures.

A pure and accurately recorded ancestry is thus to be considered as the
most important condition of success in experimental plant breeding. Next
to this comes the gathering of the seeds of each individual separately.
Fifty or sixty, and often more, bags of seeds are by no means uncommon
for a single experiment, and in ordinary years the harvest of my garden
is preserved in over a thousand separate lots.

Complying with these conditions, the origin of species may be seen as
easily as any other phenomenon. It is only necessary to have a plant in
a mutable condition. Not all species are in such a state at present, and
therefore I have begun by ascertaining which were stable and which were
not. These attempts, of course, had to be made in the experimental
garden, and large quantities of seed had to be procured and [27] sown.
Cultivated plants of course, had only a small chance to exhibit new
qualities, as they have been so strictly controlled during so many
years. Moreover their purity of origin is in many cases doubtful. Among
wild plants only those could be expected to reward the investigator
which were of easy cultivation. For this reason I have limited myself to
the trial of wild plants of Holland, and have had the good fortune to
find among them at least one species in a state of mutability. It was
not really a native plant, but one that had been introduced from America
and belongs to an American genus. I refer to the great evening-primrose
or the evening-primrose of Lamarck. A strain of this beautiful species
is growing in an abandoned field in the vicinity of Hilversum, at a
short distance from Amsterdam. Here it has escaped from a park and
multiplied. In doing so it has produced and is still producing quite a
number of new types, some of which may be considered as retrograde
varieties, while others evidently are of the nature of progressive
elementary species.

This interesting plant has afforded me the means of observing directly
how new species originate, and of studying the laws of these changes. My
researches have followed a double line of inquiry. On one side, I have
limited [28] myself to direct field observations, and to tests of seed,
collected from the wild plants in their native locality. Obviously the
mutations are decided within the seed, and the culture of young plants
from them had no other aim than that of ascertaining what had occurred
in the field. And then the many chances of destruction that threaten
young plants in a wild state, could be avoided in the garden, where
environmental factors can be controlled.

My second line of inquiry was an experimental repetition of the
phenomena which were only partly discerned at the native locality. It
was not my aim to intrude into the process, nor to try to bring out new
features. My only object was to submit to the precepts just given
concerning pure treatment, individual seed gathering, exclusion of
crosses and accurate recording of all the facts. The result has been a
pedigree which now permits of stating the relation between all the
descendants of my original introduced plant. This pedigree at once
exhibits the laws followed by the mutating species. The main fact is,
that it does not change itself gradually, but remains unaffected during
all succeeding generations. It only throws off new forms, which are
sharply contrasted with the parent, and which are from the very
beginning as perfect and as constant, as narrowly [29] defined and as
pure of type as might be expected of any species.

These new species are not produced once or in single individuals, but
yearly and in large numbers. The whole phenomenon conveys the idea of a
close group of mutations, all belonging to one single condition of
mutability. Of course this mutable state must have had a beginning, as
it must sometime come to an end. It is to be considered as a period
within the life-time of the species and probably it is only a small part
of it.

The detailed description of this experiment, however, I must delay to a
subsequent lecture, but I may be allowed to state, that the discovery of
this period of mutability is of a definite theoretical importance. One
of the greatest objections to the Darwinian theory of descent arose from
the length of time it would require, if all evolution was to be
explained on the theory of slow and nearly invisible changes. This
difficulty is at once met and fully surmounted by the hypothesis of
periodical but sudden and quite noticeable steps. This assumption
requires only a limited number of mutative periods, which might well
occur within the time allowed by physicists and geologists for the
existence of animal and vegetable life on the earth.

[30] Summing up the main points of these introductory remarks, I propose
to deal with the subjects mentioned above at some length, devoting to
each of them, if possible at least an entire lecture. The decisive facts
and discussions upon which the conclusions are based will be given in
every case. Likewise I hope to point out the weak places and the lacunae
in our present knowledge, and to show the way in which each of you may
try to contribute his part towards the advancement of science in this
subject. Lastly I shall try to prove that sudden mutation is the normal
way in which nature produces new species and new varieties. These
mutations are more readily accessible to observation and experiment than
the slow and gradual changes surmised by Wallace and his followers,
which are entirely beyond our present and future experience.

The theory of mutations is a starting-point for direct investigation,
while the general belief in slow changes has held back science from such
investigations during half a century.

Coming now to the subdivisions and headings under which my material is
to be presented, I propose describing first the real nature of the
elementary species and retrograde varieties, both in normal form and in
hybridizations. A discussion of other types of varieties, including [31]
monstrosities will complete the general plan. The second subdivision
will deal with the origin of species and varieties as taught by
experiment and observation, treating separately the sudden variations
which to my mind do produce new forms, and subsequently the fluctuations
which I hold to be not adequate to this purpose.


[32]
B. ELEMENTARY SPECIES

LECTURE II

ELEMENTARY SPECIES IN NATURE

What are species? Species are considered as the true units of nature by
the vast majority of biologists. They have gained this high rank in our
estimation principally through the influence of Linnaeus. They have
supplanted the genera which were the accepted units before Linnaeus.
They are now to be replaced in their turn, by smaller types, for reasons
which do not rest upon comparative studies but upon direct experimental
evidence.

Biological studies and practical interests alike make new demands upon
systematic botany. Species are not only the subject-material of herbaria
and collections, but they are living entities, and their life-history
and life-conditions command a gradually increasing interest. One phase
of the question is to determine the easiest manner to deal with the
collected forms of a country, and another feature is the problem [33] as
to what groups are real units and will remain constant and unchanged
through all the years of our observations.

Before Linnaeus, the genera were the real units of the system. De
Candolle pointed out that the old common names of plants, such as roses
and clover, poplars and oaks, nearly all refer to genera. The type of
the clovers is rich in color, and the shape of the flower-heads and the
single flowers escape ordinary observation; but notwithstanding this,
clovers are easily recognized, even if new types come to hand. White and
red clovers and many other species are distinguished simply by
adjectives, the generic name remaining the same for all.

Tournefort, who lived in the second half of the 17th century
(1656-1708), is generally considered as the author of genera in
systematic botany. He adopted, what was at that time the general
conception and applied it throughout the vegetable kingdom. He grouped
the new and the rare and the previously overlooked forms in the same
manner in which the more conspicuous plants were already arranged by
universal consent. Species were distinguished by minor marks and often
indicated by short descriptions, but they were considered of secondary
importance.

Based on the idea of a direct creation of all [34] living beings, the
genera were then accepted as the created forms. They were therefore
regarded as the real existing types, and it was generally surmised that
species and varieties owed their origin to subsequent changes under the
influence of external conditions. Even Linnaeus agreed with this view in
his first treatises and in his "Philosophical Botany" he still kept to
the idea that all genera had been created at once with the beginning of
life.

Afterwards Linnaeus changed his opinion on this important point, and
adopted species as the units of the system. He declared them to be the
created forms, and by this decree, at once reduced the genera to the
rank of artificial groups. Linnaeus was well aware that this conception
was wholly arbitrary, and that even the species are not real indivisible
entities. But he simply forbade the study of lesser subdivisions. At his
time he was quite justified in doing so, because the first task of the
systematic botanists was the clearing up of the chaos of forms and the
bringing of them into connection with their real allies.

Linnaeus himself designated the subdivisions of the species as
varieties, but in doing so he followed two clearly distinct principles.
In some cases his species were real plants, and the varieties seemed to
be derived from them by [35] some simple changes. They were subordinated
to the parent-species. In other cases his species were groups of lesser
forms of equal value, and it was not possible to discern which was the
primary and which were the derivatives.

These two methods of subdivision seem in the main, and notwithstanding
their relatively imperfect application in many single examples, to
correspond with two really distinct cases. The derivative varieties are
distinguished from the parent-species by some single, but striking mark,
and often this attribute manifests itself as the loss of some apparent
quality. The loss of spines and of hairs and the loss of blue and red
flower-colors are the most notorious, but in rarer cases many single
peculiarities may disappear, thereby constituting a variety. This
relation of varieties to the parent-species is gradually increasing in
importance in the estimation of botanists, sharply contrasting with
those cases, in which such dependency is not to be met with.

If among the subdivisions of a species, no single one can be pointed out
as playing a primary part, and the others can not be traced back to it,
the relation between these lesser units is of course of another
character. They are to be considered of equal importance. They are
distinguished from each other by more than [36] one character, often by
slight differences in nearly all their organs and qualities. Such forms
have come to be designated as "elementary species." They are only
varieties in a broad and vague systematic significance of the word, not
in the sense accorded to this term in horticultural usage, nor in a
sharper and more scientific conception.

Genera and species are, at the present time, for a large part
artificial, or stated more correctly, conventional groups. Every
systematist is free to delimit them in a wider or in a narrower sense,
according to his judgment. The greater authorities have as a rule
preferred larger genera, others of late have elevated innumerable
subgenera to the rank of genera. This would work no real harm, if
unfortunately, the names of the plants had not to be changed each time,
according to current ideas concerning genera. Quite the same inconstancy
is observed with species. In the Handbook of the British Flora, Bentham
and Hooker describe the forms of brambles under 5 species, while
Babington in his Manual of British Botany makes 45 species out of the
same material. So also in other cases. For instance, the willows which
have 13 species in one and 31 species in the other of these manuals, and
the hawkweeds for which the figures are 7 and 32 [37] respectively.
Other authors have made still greater numbers of species in the same
groups.

It is very difficult to estimate systematic differences on the ground of
comparative studies alone. All sorts of variability occur, and no
individual or small group of specimens can really be considered as a
reliable representative of the supposed type. Many original diagnoses of
new species have been founded on divergent specimens and of course, the
type can afterwards neither be derived from this individual, nor from
the diagnosis given.

This chaotic state of things has brought some botanists to the
conviction that even in systematic studies only direct experimental
evidence can be relied upon. This conception has induced them to test
the constancy of species and varieties, and to admit as real units only
such groups of individuals as prove to be uniform and constant
throughout succeeding generations. The late Alexis Jordan, of Lyons in
France, made extensive cultures in this direction. In doing so, he
discovered that systematic species, as a rule, comprise some lesser
forms, which often cannot easily be distinguished when grown in
different regions, or by comparing dried material. This fact was, of
course, most distasteful to the systematists of his time and even for a
long period afterwards [38] they attempted to discredit it. Milde and
many others have opposed these new ideas with some temporary success.
Only of late has the school of Jordan received due recognition, after
Thuret, de Bary, Rosen and others tested its practices and openly
pronounced for them. Of late Wittrock of Sweden has joined them, making
extensive experimental studies concerning the real units of some of the
larger species of his country.

From the evidence given by these eminent authorities, we may conclude
that systematic species, as they are accepted nowadays, are as a rule
compound groups. Sometimes they consist of two or three, or a few
elementary types, but in other cases they comprise twenty, or fifty, or
even hundreds of constant and well differentiated forms.

The inner constitution of these groups is however, not at all the same
in all cases. This will be seen by the description of some of the more
interesting of them. The European heartsease, from which our
garden-pansies have been chiefly derived, will serve as an example. The
garden-pansies are a hybrid race, won by crossing the _Viola tricolor_
with the large flowered and bright yellow _V. lutea_. They combine, as
everyone knows, in their wide range of [39] varieties, the attributes of
the latter with the peculiarities of the former species.

Besides the _lutea_, there are some other species, nearly allied to
tricolor, as for instance, _cornuta_, _calcarata_, and _altaica_, which
are combined with it under the head of _Melanium_ as a subgenus, and
which together constitute a systematic unity of undoubted value, but
ranging between the common conceptions of genus and species. These forms
are so nearly allied to the heartsease that they have of late been made
use of in crosses, in order to widen the range of variability of
garden-pansies.

_Viola tricolor_ is a common European weed. It is widely dispersed and
very abundant, growing in many localities in large numbers. It is an
annual and ripens its seeds freely, and if opportunity is afforded, it
multiplies rapidly.

_Viola tricolor_ has three subspecies, which have been elevated to the
rank of species by some authors, and which may here be called, for
brevity's sake, by their binary names. One is the typical _V. tricolor_,
with broad flowers, variously colored and veined with yellow, purple and
white. It occurs in waste places on sandy soil. The second is called _V.
arvensis_ or the field-pansy; it has small inconspicuous flowers, with
pale-yellowish petals which are shorter than the sepals. It pollinates
itself without the [40] aid of insects, and is widely dispersed in
cultivated fields. The third form, _V. alpestris_, grows in the Alps,
but is of lesser importance for our present discussion.

Anywhere throughout the central part of Europe _V. tricolor_ and _V.
arvensis_ may be seen, each occupying its own locality. They may be
considered as ranging among the most common native plants of the
particular regions they inhabit. They vary in the color of the flowers,
branching of the stems, in the foliage and other parts, but not to such
an extent as to constitute distinct strains. They have been brought into
cultivation by Jordan, Wittrock and others, but throughout Europe each
of them constitutes a single type.

These types must be very old and constant, fluctuating always within the
same distinct and narrow limits. No slow, gradual changes can have taken
place. In different countries their various habitats are as old as the
historical records, and probably many centuries older. They are quite
independent of one another, the distance being in numerous cases far too
great for the exchange of pollen or of seeds. If slow and gradual
changes were the rule, the types could not have remained so uniform
throughout the whole range of these two species. They would necessarily
have split up into thousands [41] and thousands of minor races, which
would show their peculiar characteristics if tested by cultures in
adjacent beds. This however, is not what happens. As a matter of fact
_V. tricolor_ and _V. arvensis_ are widely distributed but wholly
constant types.

Besides these, there occur distinct types in numerous localities. Some
of them evidently have had time and opportunity to spread more or less
widely and now occupy larger regions or even whole countries. Others are
narrowly limited, being restricted to a single locality. Wittrock
collected seeds or plants from as many localities as possible in
different parts of Sweden and neighboring states and sowed them in his
garden near Stockholm. He secured seeds from his plants, and grew from
them a second, and in many cases a third generation in order to estimate
the amount of variability. As a rule the forms introduced into his
garden proved constant, notwithstanding the new and abnormal conditions
under which they were propagated.

First of all we may mention three perennial forms called by him _Viola
tricolor ammotropha_, _V. tricolor coniophila_ and _V. stenochila_. The
typical _V. tricolor_ is an annual plant; sowing itself in summer and
germinating soon afterwards. The young plants thrive throughout [42] the
latter part of the summer and during the fall, reaching an advanced
stage of development of the branched stems before winter. Early in the
spring the flowers begin to open, but after the ripening of the seeds
the whole plant dies.

The three perennial species just mentioned develop in the same manner in
the first year. During their flowering period, however, and afterwards,
they produce new shoots from the lower parts of the stem. They prefer
dry and sandy soils, often becoming covered with the sand that is blown
on them by the winds. They are prepared for such seemingly adverse
circumstances by the accumulation of food in the older stems and by the
capacity of the new shoots to thrive on this food till they have become
long enough to reach the light. _V. tricolor ammotropha_ is native near
Ystad in Sweden, and the other two forms on Gotland. All three have
narrowly limited habitats.

The typical tricolored heartsease has remained annual in all its other
subspecies. It may be divided into two types in the first place, _V.
tricolor genuina_ and _V. tricolor versicolor_. Both of them have a wide
distribution and seem to be the prototypes from which the rarer forms
must have been derived. Among these latter Wittrock describes seven
local types, which [43] proved to be constant in his pedigree-cultures.
Some of them have produced other forms, related to them in the way of
varieties. They all have nearly the same general habit and do not
exhibit any marked differences in their growth, in the structure and
branching of the stems, or in the character of their foliage.
Differentiating points are to be found mainly in the colors and patterns
of the flowers. The veins, which radiate from the centre of the corolla
are branched in some and undivided in others; in one elementary species
they are wholly lacking. The purple color may be absent, leaving the
flowers of a pale or a deep yellow. Or the purple may be reddish or
bluish. Of the petals all five may have the purple hue on their tips, or
this attribute may be limited to the two upper ones. Contrasting with
this wide variability is the stability of the yellow spot in the centre,
which is always present and becomes inconspicuous only, when the whole
petals are of the same hue. It is a general conception that colors and
color-markings are liable to great variability and do not constitute
reliable standards. But the cultures of Wittrock have proved the
contrary, at least in the case of the violets. No pattern, however
quaint, appears changeable, if one elementary species only is
considered. Hundreds of plants from seeds [44] from one locality may be
grown, and all will exhibit exactly the same markings. Most of these
forms are of very local occurrence. The most beautiful of all, the
_ornatissima_, is found only in Jemtland, the _aurobadia_ only in
Sodermanland, the anopetala_ in other localities in the same country,
the _roseola_ near Stockholm, and the yellow _lutescens_ in Finmarken.

The researches of Wittrock included only a small number of elementary
species, but every one who has observed the violets in the central parts
of Europe must be convinced that many dozens of constant forms of the
typical _Viola tricolor_ might easily be found and isolated.

We now come to the field pansy, the _Viola arvensis_, a very common weed
in the grain-fields of central Europe. I have already mentioned its
small corolla, surpassed by the lobes of the calyx and its capacity of
self-fertilization. It has still other curious differentiating
characters; the pollen grains, which are square in _V. tricolor_, are
five-sided in _V. arvensis_. Some transgressive fluctuating variability
may occur in both cases through the admixture of pollen-grains. Even
three-angled pollen grains are seen sometimes. Other marks are observed
in the form of the anthers and the spur.

There seem to be very many local subspecies [45] of the field-pansy.
Jordan has described some from the vicinity of Lyons, and Wittrock
others from the northern parts of Europe. They diverge from their common
prototype in nearly all attributes, the flowers not showing the
essential differentiating characters as in the _V. tricolor_. Some have
their flower-stalks erect, and in others the flowers are held nearly at
right angles to the stem. _V. pallescens_ is a small, almost unbranched
species with small pale flowers. _V. segetalis_ is a stouter species
with two dark blue spots on the tips of the upper petals. _V. agrestis_
is a tall and branched, hairy form. _V. nemausensis_ attains a height of
only 10 cm., has rounded leaves and long flower-stalks. Even the seeds
afford characters which may be made use of in isolating the various
species.

The above-mentioned elementary forms belong to the flora of southern
France, and Wittrock has isolated and cultivated a number of others from
the fields of Sweden. A species from Stockholm is called _Viola patens_;
_V. arvensis curtisepala_ occurs in Gotland, and _V. arvensis striolata_
is a distinct form, which has appeared in his cultures without its true
origin being ascertained.

The alpine violets comprise a more widespread type with some local
elementary species [46] derived exactly in the same way as the
tricolored field pansies.

Summarizing the general result of this description we see that the
original species _Viola tricolor_ may be split up into larger and lesser
groups of separate forms. These last prove to be constant in
pedigree-cultures, and therefore are to be considered as really existent
units. They are very numerous, comprising many dozens in each of the two
larger subdivisions.

All systematic grouping of these forms, and their combination into
subspecies and species rests on the comparative study of their
characters. The result of such studies must necessarily depend on
principles which underlie them. According to the choice of these
principles, the construction of the groups will be found to be
different. Wittrock trusts in the first place to morphologic characters,
and considers the development as passing from the more simple to the
more complex types. On the other hand the geographic distribution may be
considered as an indication of the direction of evolution, the
wide-spread forms being regarded as the common parents of the minor
local species.

However, such considerations are only of secondary importance. It must
be borne in mind that an ordinary systematic species may include [47]
many dozens of elementary forms, each of which remains constant and
unchanged in successive generations, even if cultivated in the same
garden and under similar external conditions.

Leaving the violets, we may take the vernal whitlow-grass or _Draba
verna_ for a second illustration. This little annual cruciferous plant
is common in the fields of many parts of the United States, though
originally introduced from Europe. It has small basal rosettes which
develop during summer and winter, and produce numerous leafless
flowering stems early in the spring. It is a native of central Europe
and western Asia, and may be considered as one of the most common
plants, occurring anywhere in immense numbers on sandy soils. Jordan was
the first to point out that it is not the same throughout its entire
range. Although a hasty survey does not reveal differences, they show
themselves on closer inspection. De Bary, Thuret, Rosen and many others
confirmed this result, and repeated the pedigree-cultures of Jordan.
Every type is constant and remains unchanged in successive generations.
The anthers open in the flower-buds and pollinate the stigmas before the
expansion of the flowers, thus assuring self-fertilization. Moreover,
these inconspicuous little flowers are only sparingly visited by
insects. Dozens of subspecies [48] may be cultivated in the same garden
without any real danger of their intercrossing. They remain as pure as
under perfect isolation.

It is very interesting to observe the aspect of such types, when growing
near each other. Hundreds of rosettes exhibit one type, and are
undoubtedly similar. The alternative group is distinguishable at first
sight, though the differentiating marks are often so slight as to be
traceable with difficulty. Two elementary species occur in Holland, one
with narrow leaves in the western provinces and one with broader foliage
in the northern parts. I have cultivated them side by side, and was as
much struck with the uniformity within each group, as with the contrast
between the two sets.

Nearly all organs show differences. The most marked are those of the
leaves, which may be small or large, linear or elliptic or oblong and
even rhomboidal in shape, more or less hairy with simple or with
stellate branched hairs, and finally of a pure green or of a glaucous
color. The petals are as a rule obcordate, but this type may be combined
with others having more or less broad emarginations at the summit, and
with differences in breadth which vary from almost linear types to
others which touch along their margins. The pods are short and broad, or
long and narrow, or varying in sundry other [49] ways. All in all there
are constant differences which are so great that it has been possible to
distinguish and to describe large numbers of types.

Many of them have been tested as to their constancy from seed. Jordan
made numerous cultures, some of which lasted ten or twelve years; Thuret
has verified the assertion concerning their constancy by cultures
extending over seven years in some instances; Villars and de Bary made
numerous trials of shorter duration. All agree as to the main points.
The local races are uniform and come true from seed; the variability of
the species is not of a fluctuating, but of a polymorphous nature. A
given elementary species keeps within its limits and cannot vary beyond
them, but the whole group gives the impression of variability by its
wide range of distinct, but nearly allied forms.

The geographic distribution of these elementary species of the
whitlow-grass is quite distinct from that of the violets. Here
predominant species are limited to restricted localities. Most of them
occupy one or more departments of France, and in Holland two of them are
spread over several provinces. An important number are native in the
centre of Europe, and from the vicinity of Lyons, Jordan succeeded in
establishing about fifty elementary [50] species in his garden. In this
region they are crowded together and not rarely two or even more quite
distinct forms are observed to grow side by side on the same spot.
Farther away from this center they are more widely dispersed, each
holding its own in its habitat. In all, Jordan has distinguished about
two hundred species of _Draba verna_ from Europe and western Asia.
Subsequent authors have added new types to the already existing number
from time to time.

The constancy of these elementary species is directly proven by the
experiments quoted above, and moreover it may be deduced from the
uniformity of each type within its own domain. These are so large that
most of the localities are practically isolated from one another, and
must have been so for centuries. If the types were slowly changing such
localities would often, though of course not always, exhibit slighter
differences, and on the geographic limits of neighboring species
intermediates would be found. Such however, are not on record. Hence the
elementary species must be regarded as old and constant types.

The question naturally arises how these groups of nearly allied forms
may originally have been produced. Granting a common origin for all of
them, the changes may have been [51] simultaneous or successive.
According to the geographic distribution, the place of common origin
must probably be sought in the southern part of central Europe, perhaps
even in the vicinity of Lyons. Here we may assume that the old _Draba
verna_ has produced a host or a swarm of new types. Thence they must
have spread over Europe, but whether in doing so they have remained
constant, or whether some or many of them have repeatedly undergone
specific mutations, is of course unknown.

The main fact is, that such a small species as _Draba verna_ is not at
all a uniform type, but comprises over two hundred well distinguished
and constant forms.

It is readily granted that violets and whitlowgrasses are extreme
instances of systematic variability. Such great numbers of elementary
species are not often included in single species of the system. But the
numbers are of secondary importance, and the fact that systematic
species consist, as a rule, of more than one independent and constant
subspecies, retains its almost universal validity.

In some cases the systematic species are manifest groups, sharply
differentiated from one another. In other instances the groups of
elementary forms as they are shown by direct observation, have been
adjudged by many authors [52] to be too large to constitute species.
Hence the polymorphous genera, concerning the systematic subdivisions of
which hardly two authors agree. Brambles and roses are widely known
instances, but oaks, elms, apples, and pears, _Mentha_, _Prunu_s,
_Vitis_, _Lactuca_, _Cucumis_, _Cucurbita_ and numerous others are in
the same condition.

In some instances the existence of elementary species is so obvious,
that they have been described by taxonomists as systematic varieties or
even as good species. The primroses afford a widely known example.
Linnaeus called them _Primula veris_, and recognized three types as
pertaining to this species, but Jacquin and others have elevated these
subspecies to the full rank of species. They now bear the names of
_Primula elatior_ with larger, _P. officinalis_ with smaller flowers,
and _P. acaulis_. In the last named the common flower-stalk is lacking
and the flowers of the umbel seem to be borne in the arils of the basal
leaves.

In other genera such nearly allied species are more or less universally
recognized. _Galium Mollugo_ has been divided into _G. elatum_ with a
long and weak stem, and _G. erectum_ with shorter and erect stems;
_Cochlearia danica_, _anglica_ and _officinalis_ are so nearly allied as
to be hardly distinguishable. _Sagina apetala_ and _patula_, [53]
_Spergula media_ and _salina_ and many other pairs of allied species
have differentiating characters of the same value as those of the
elementary species of _Draba verna_. _Filago_, _Plantago_, _Carex_,
_Ficaria_ and a long series of other genera afford proofs of the same
close relation between smaller and larger groups of species. The
European frost-weeds or _Helianthemum_ include a group of species which
are so closely allied, that ordinary botanical descriptions are not
adequate to give any idea of their differentiating features. It is
almost impossible to determine them by means of the common analytical
keys. They have to be gathered from their various native localities and
cultivated side by side in the garden to bring out their differences.
Among the species of France, according to Jordan, _Helianthemum
polifolium_, _H. apenninum_, _H. pilosum_ and _H. pulverulentum_ are of
this character.

A species of cinquefoil, _Potentilla Tormentilla_, which is
distinguished by its quaternate flowers, occurs in Holland in two
distinct types, which have proved constant in my cultural experiments.
One of them has, broad petals, meeting together at the edges, and
constituting rounded saucer without breaks. The other has narrow petals,
which are strikingly separated from one another and show the sepals
between them. [54] In the same manner bluebells vary in the size and
shape of the corolla, which may be wide or narrow, bell-shaped or
conical, with the tips turned downwards, sidewards or backwards.

As a rule all of the more striking elementary types have been described
by local botanists under distinct specific names, while they are thrown
together into the larger systematic species by other authors, who study
the distribution of plants over larger portions of the world. Everything
depends on the point of view taken. Large floras require large species.
But the study of local floras yields the best results if the many forms
of the region are distinguished and described as completely as possible.
And the easiest way is to give to each of them a specific name. If two
or more elementary species are united in the same district, they are
often treated in this way, but if each region had its own type of some
given species, commonly the part is taken for the whole, and the sundry
forms are described under the same name, without further distinctions.

Of course these questions are all of a practical and conventional
nature, but involve the different methods in which different authors
deal with the same general fact. The fact is that systematic species are
compound groups, exactly like the genera and that their real units [55]
can only be recognized by comparative experimental studies.

Though the evidence already given might be esteemed to be sufficient for
our purpose, I should like to introduce a few more examples; two of them
pertain to American plants.

The Ipecac spurge or _Euphorbia Ipecacuanha_ occurs from Connecticut to
Florida, mainly near the coast, preferring dry and sandy soil. It is
often found by the roadsides. According to Britton and Brown's
"Illustrated Flora" it is glabrous or pubescent, with several or many
stems, ascending or nearly erect; with green or red leaves, which are
wonderfully variable in outline, from linear to orbicular, mostly
opposite, the upper sometimes whorled, the lower often alternate. The
glands of the involucres are elliptic or oblong, and even the seeds vary
in shape.

Such a wide range of variability evidently points to the existence of
some minor types. Dr. John Harshberger has made a study of those which
occur in the vicinity of Whitings in New Jersey. His types agree with
the description given above. Others were gathered by him at Brown's
Mills in the pinelands, New Jersey, where they grew in almost pure sand
in the bright sunlight. He observed still other differentiating
characters. The amount of seed [56] produced and the time of flowering
were variable to a remarkable degree.

Dr. Harshberger had the kindness to send me some dried specimens of the
most interesting of these types. They show that the peculiarities are
individual, and that each specimen has its own characters. It is very
probable that a comparative experimental study will prove the existence
of a large number of elementary species, differing in many points; they
will probably also show differences in the amount of the active chemical
substances, especially of emetine, which is usually recorded as present
in about 1%, but which will undoubtedly be found in larger quantities in
some, and in smaller quantities in other elementary species. In this way
the close and careful distinction of the really existing units might
perhaps prove of practical importance.

MacFarlane has studied the beach-plum or _Prunus maritima_, which is
abundant along the coast regions of the Eastern States from Virginia to
New Brunswick. It often covers areas from two to two hundred acres in
extent, sometimes to the exclusion of other plants. It is most prolific
on soft drifting sand near the sea or along the shore, where it may at
times be washed with ocean-spray. The fruit usually become ripe about
the middle of August, and show extreme [57] variations in size, shape,
color, taste, consistency and maturation period, indicating the
existence of separate races or elementary species, with widely differing
qualities. The earlier varieties begin to ripen from August 10 to 20,
and a continuous supply can be had till September 10, while a few good
varieties continue to ripen till September 20. But even late in October
some other types are still found maturing their fruits.

Exact studies were made of fruit and stone variations, and their
characteristics as to color, weight, size, shape and consistency were
fully described. Similar variations have been observed, as is well
known, in the cultivated plums. Fine blue-black fruits were seen on some
shrubs and purplish or yellow fruits on others. Some exhibit a firmer
texture and others a more watery pulp. Even the stones show differences
which are suggestive of distinct races.

Recently Mr. Luther Burbank of Santa Rosa, California, has made use of
the beach-plum to produce useful new varieties. He observed that it is a
very hardy species, and never fails to bear, growing under the most
trying conditions of dry and sandy, or of rocky and even of heavy soil.
The fruits of the wild shrubs are utterly worthless for anything but
preserving. [58] But by means of crossing with other species and
especially with the Japanese plums, the hardy qualities of the
beach-plum have been united with the size, flavor and other valuable
qualities of the fruit, and a group of new plums have been produced with
bright colors, ovoid and globular forms which are never flattened and
have no suture. The experiments were not finished, when I visited Mr.
Burbank in July, 1904, and still more startling improvements were said
to have been secured.

I may perhaps be allowed to avail myself of this opportunity to point
out a practical side of the study of elementary species. This always
appears whenever wild plants are subjected to cultivation, either in
order to reproduce them as pure strains, or to cross them with other
already cultivated species. The latter practice is as a rule made use of
whenever a wild species is found to be in possession of some quality
which is considered as desirable for the cultivated forms. In the case
of the beach-plum it is the hardiness and the great abundance of fruits
of the wild species which might profitably be combined with the
recognized qualities of the ordinary plums. Now it is manifest, that in
order to make crosses, distinct individual plants are to be chosen, and
that the variability of the wild species may be of very great
importance. [59] Among the range of elementary species those should be
used which not only possess the desired advantages in the highest
degree, but which promise the best results in other respects or their
earliest attainment. The fuller our knowledge of the elementary species
constituting the systematic groups, the easier and the more reliable
will be the choice for the breeder. Many Californian wild flowers with
bright colors seem to consist of large numbers of constant elementary
forms, as for instance, the lilies, godetias, eschscholtias and others.
They have been brought into cultivation many times, but the minutest
distinction of their elementary forms is required to attain the highest
success.

In concluding, I will point out a very interesting difficulty, which in
some cases impedes the clear understanding of elementary species. It is
the lack of self-fertilization. It occurs in widely distant families,
but has a special interest for us in two genera, which are generally
known as very polymorphous groups.

One of them is the hawkweed or _Hieracium_, and the other is the
dandelion or _Taraxacum officinale_. Hawkweeds are known as a genus in
which the delimitation of the species is almost impossible, Thousands of
forms may be cultivated side by side in botanical gardens, exhibiting
[60] slight but undoubted differentiating features, and reproduce
themselves truly by seed. Descriptions were formerly difficult and so
complicated that the ablest writers on this genus, Fries and Nageli are
said not to have been able to recognize the separate species by the
descriptions given by each other. Are these types to be considered as
elementary species, or only as individual differences? The decision of
course, would depend upon their behavior in cultures. Such tests have
been made by various experimenters. In the dandelion the bracts of the
involucre give the best characters. The inner ones may be linear or
linear-lanceolate, with or without appendages below the tip; the outer
ones may be similar and only shorter, or noticeably larger, erect,
spreading or even reflexed, and the color of the involucre may be a pure
green or glaucous; the leaves may be nearly entire or pinnatifid, or
sinuate-dentate, or very deeply runcinate-pinnatifid, or even pinnately
divided, the whole plant being more or less glabrous.

Raunkiaer, who has studied experimentally a dozen types from Denmark,
found them constant, but observed that some of them have no pollen at
all, while in others the pollen, though present, is impotent. It does
not germinate on the stigma, cannot produce the ordinary tube, [61] and
hence has no fertilizing power. But the young ovaries do not need such
fertilization. They are sufficient unto themselves. One may cut off all
the flowers of a head before the opening of the anthers, and leave the
ovaries untouched, and the head will ripen its seeds quite as well. The
same thing occurs in the hawkweeds. Here, therefore, we have no
fertilization and the extensive widening of the variability, which
generally accompanies this process is, of course, wanting. Only partial
or vegetative variability is present. Unfertilized eggs when developing
into embryos are equivalent to buds, separated from the parent-plant and
planted for themselves. They repeat both the specific and the individual
characters of the parent. In the case of the hawkweed and the dandelion
there is at present no means of distinguishing between these two
contrasting causes of variability. But like the garden varieties which
are always propagated in the vegetative way, their constancy and
uniformity are only apparent and afford no real indication of hereditary
qualities.

In addition to these and other exceptional cases, seed-cultures are
henceforth to be considered as the sole means of recognizing the really
existing systematic units of nature. All other groups, including
systematic species and [62] genera, are equally artificial or
conventional. In other words we may state "that current misconceptions
as to the extreme range of fluctuating variability of many native
species have generally arisen from a failure to recognize the composite
nature of the forms in question," as has been demonstrated by MacDougal
in the case of the common evening-primrose, _Oenothera biennis_. "It is
evident that to study the behavior of the characters of plants we must
have them in their simplest combinations; to investigate the origin and
movements of species we must deal with them singly and uncomplicated."


[63]

LECTURE III

ELEMENTARY SPECIES OF CULTIVATED PLANTS

Recalling the results of the last lecture, we see that the species of
the systematists are not in reality units, though in the ordinary course
of floristic studies they may, as a rule, seem to be so. In some cases
representatives of the same species from different countries or regions,
when compared with one another do not exactly agree. Many species of
ferns afford instances of this rule, and Lindley and other great
systematists have frequently been puzzled by the wide range of
differences between the individuals of a single species.

In other cases the differing forms are observed to grow near each other,
sometimes in neighboring provinces, sometimes in the same locality,
growing and flowering in mixtures of two or three or even more
elementary types. The violets exhibit widespread ancient types, from
which the local species may be taken to have arisen. The common
ancestors of the Whitlow-grasses are probably not to be found [64] among
existing forms, but numerous types are crowded together in the southern
part of central Europe and more thinly scattered elsewhere, even as far
as western Asia. There can be little doubt that their common origin is
to be sought in the center of their geographic distribution.

Numerous other cases exhibit smaller numbers of elementary units within
a systematic species; in fact purely uniform species seem to be
relatively rare. But with small numbers there are of course no
indications to be expected concerning their common origin or the
starting point of their distribution.

It is manifest that these experiences with wild species must find a
parallel among cultivated plants. Of course cultivated plants were
originally wild and must have come under the general law. Hence we may
conclude that when first observed and taken up by man, they must already
have consisted of sundry elementary subspecies. And we may confidently
assert that some must have been rich and others poor in such types.

Granting this state of things as the only probable one, we can easily
imagine what must have been the consequences. If a wild species had been
taken into cultivation only once, the cultivated form would have been a
single elementary [65] type. But it is not very likely that such
partiality would occur often. The conception that different tribes at
different times and in distant countries would have used the wild plants
of their native regions seems far more natural than that all should have
obtained plants for cultivation from the same source or locality. If
this theory may be relied upon, the origin of many of the more widely
cultivated agricultural plants must have been multiple, and the number
of the original elementary species of the cultivated types must have
been so much the larger, the more widely distributed and variable the
plants under consideration were before the first period of cultivation.

Further it would seem only natural to explain the wide variability of
many of our larger agricultural and horticultural stocks by such an
incipient multiformity of the species themselves. Through commercial
intercourse the various types might have become mixed so as to make it
quite impossible to point out the native localities for each of them.

Unfortunately historical evidence on this point is almost wholly
lacking. The differences in question could not have been appreciated at
that remote period, and interest the common observer but little even
today. The history of most of the cultivated plants is very obscure,
[66] and even the most skillful historians, by sifting the evidence
afforded by the older writers, and that obtained by comparative
linguistic investigations have been able to do little more than frame
the most general outline of the cultural history of the most common and
most widely used plants.

Some authors assume that cultivation itself might have been the
principal cause of variability, but it is not proved, nor even probable,
that cultivated plants are intrinsically more variable than their wild
prototypes. Appearances in this case are very deceptive. Of course
widely distributed plants are as a rule richer in subspecies than forms
with limited distribution, and the former must have had a better chance
to be taken into cultivation than the latter. In many cases, especially
with the more recent cultivated species, man has deliberately chosen
variable forms, because of their greater promise. Thirdly, wide
variability is the most efficient means of acclimatization, and only
species with many elementary units would have offered the adequate
material for introduction into new countries.

From this discussion it would seem that it is more reasonable to assert
that variability is one of the causes of the success of cultivation,
than to assume that cultivation is a cause of variability [67] at large.
And this assumption would be equally sufficient to explain the existing
conditions among cultivated plants.

Of course I do not pretend to say that cultivated plants should be
expected to be less variable than in the wild state, or that swarms of
elementary species might not be produced during cultivation quite as
well as before. However the chance of such an event, as is easily seen,
cannot be very great, and we shall have to be content with a few
examples of which the coconut is a notable one.

Leaving this general discussion of the subject, we may take up the
example of the beets. The sugar-beet is only one type from among a horde
of others, and though the origin of all the single types is not
historically known, the plant is frequently found in the wild state even
at the present time, and the native types may be compared with the
corresponding cultivated varieties.

The cultivation of beets for sugar is not of very ancient date. The
Romans knew the beets and used them as vegetables, both the roots and
the leaves. They distinguished a variety with white and one with red
flesh, but whether they cultivated them, or only collected them from
where they grew spontaneously, appears to be unknown.

[68] Beets are even now found in large quantities along the shores of
Italy. They prefer the vicinity of the sea, as do so many other members
of the beet family, and are not limited to Italy, but are found growing
elsewhere on the littoral of the Mediterranean, in the Canary Islands
and through Persia and Babylonia to India. In most of their native
localities they occur in great abundance.

The color of the foliage and the size of the roots are extremely
variable. Some have red leafstalks and veins, others a uniform red or
green foliage, some have red or white or yellow roots, or exhibit
alternating rings of a red and of a white tinge on cut surfaces. It
seems only natural to consider the white and the red, and even the
variegated types as distinct varieties, which in nature do not
transgress their limits nor change into one another. In a subsequent
lecture I will show that this at least is the rule with the
corresponding color-varieties in other genera.

The fleshiness or pulpiness of the roots is still more variable. Some
are as thick as the arm and edible, others are not thicker than a finger
and of a woody composition, and the structure of this woody variety is
very interesting. The sugar-beet consists, as is generally known, of
concentric layers of sugar-tissue and of vascular [69] strands; the
larger the first and the smaller the latter, the greater is, as a rule,
the average amount of sugar of the race. Through the kindness of the
late Mr. Rimpau, a well known German breeder of sugar-beet varieties, I
obtained specimens from seed of a native wild locality near Bukharest.
The plants produced quite woody roots, showing almost no sugar tissue at
all. Woody layers of strongly developed fibrovascular strands were seen
to be separated one from another only by very thin layers of
parenchymatous cells. Even the number of layers is variable; it was
observed to be five in my plants; but in larger roots double this number
and even more may easily be met with.

Some authors have distinguished specific types among these wild forms.
While the cultivated beets are collected under the head of _Beta
vulgaris_, separate types with more or less woody roots have been
described as _Beta maritima_ and _Beta patula_. These show differences
in the habit of the stems and the foliage. Some have a strong tendency
to become annual, others to become biennial. The first of course do not
store a large quantity of food in their roots, and remain thin, even at
the time of flowering. The biennial types occur in all sizes of roots.
In the annuals the stems may vary from [70] erect to ascending, and the
name _patula_ indicates stems which are densely branching from the base
with widely spreading branches throughout. Mr. Em. von Proskowetz of
Kwassitz, Austria, kindly sent me seeds of this _Beta patula_, the
variability of which was so great in my cultures as to range from nearly
typical sugar-beets to the thin woody type of Bukharest.

Broad and narrow leaves are considered to be differentiating marks
between _Beta vulgaris_ and _Beta patula_, but even here a wide range of
forms seem to occur.

Rimpau, Proskowetz, Schindler and others have made cultures of beets
from wild localities in order to discover a hypothetical common ancestor
of all the present cultivated types. These researches point to the _B.
patula_ as the probable ancestor, but of course they were not made to
decide the question as to whether the origination of the several now
existing types had taken place before or during culture. From a general
point of view the variability of the wild species is parallel to that of
the cultivated forms to such a degree as to suggest the multiple origin
of the former. But a close investigation of this highly important
problem has still to be made.

The varieties of the cultivated beets are commonly [71] included in four
subspecies. The two smallest are the salad-beets and the ornamental
forms, the first being used as food, and ordinarily cultivated in red
varieties, the second being used as ornamental plants during the fall,
when they fill the beds left empty by summer flowers, with a bright
foliage that is exceedingly rich in form and color. Of the remaining
subspecies, one comprises the numerous sorts cultivated as forage-crops
and the other the true sugar-beets. Both of them vary widely as to the
shape and the size of the roots, the quality of the tissue, the foliage
and other characteristics.

Some of these forms, no doubt, have originated during culture. Most of
them have been improved by selection, and no beet found in the wild
state ever rivals any cultivated variety. But the improvement chiefly
affects the size, the amount of sugar and nutrient substances and some
other qualities which recur in most of the varieties. The varietal
attributes themselves however, are more or less of a specific nature,
and have no relation to the real industrial value of the race. The
short-rooted and the horn-shaped varieties might best be cited as
examples.

The assertion that the sundry varieties of forage-beets are not the
result of artificial selection, [72] is supported in a large measure by
the historic fact that the most of them are far older than the method of
conscious selection of plants itself. This method is due to Louis
Vilmorin and dates from the middle of the last century. But in the
sixteenth century most of our present varieties of beets were already in
cultivation. Caspar Bauhin gives a list of the beets of his time and it
is not difficult to recognize in it a large series of subspecies and
varieties and even of special forms, which are still cultivated. A more
complete list was published towards the close of the same century by
Olivier de Serres in his world-renowned "Theatre d'Agriculture" (Paris,
1600).

The red forage-beets which are now cultivated on so large a scale, had
been introduced from Italy into France only a short time before.

From this historic evidence, the period during which the beets were
cultivated from the time of the Romans or perhaps much later, up to the
time of Bauhin and De Serres, would seem far too short for the
production by the unguided selection of man of all the now existing
types. On the other hand, the parallelism between the characters of some
wild and some cultivated varieties goes to make it very probable that
other varieties have been found in the same way, some in this country
and others in that, [73] and have been taken into cultivation
separately. Afterwards of course all must have been improved in the
direction required by the needs of man.

Quite the same conclusion is afforded by apples. The facts are to some
extent of another character, and the rule of the derivation of the
present cultivated varieties from original wild forms can be illustrated
in this case in a more direct way. Of course we must limit ourselves to
the varieties of pure ancestry and leave aside all those which are of
hybrid or presumably hybrid origin.

Before considering their present state of culture, something must be,
said about the earlier history and the wild state of the apples.

The apple-tree is a common shrub in woods throughout all parts of
Europe, with the only exception of the extreme north. Its distribution
extends to Anatolia, the Caucasus and Ghilan in Persia. It is found in
nearly all forests of any extent and often in relatively large numbers
of individuals. It exhibits varietal characters, which have led to the
recognition of several spontaneous forms, especially in France and in
Germany.

The differentiating qualities relate to the shape and indumentum of the
leaves. Nothing is known botanically as to differences between [74] the
fruits of these varieties, but as a matter of fact the wild apples of
different countries are not at all the same.

Alphonse De Candolle, who made a profound study of the probable origin
of most of our cultivated plants, comes to the conclusion that the apple
tree must have had this wide distribution in prehistoric times, and that
its cultivation began in ancient times everywhere.

This very important conclusion by so high an authority throws
considerable light on the relation between cultivated and wild varieties
at large. If the historic facts go to prove a multiple origin for the
cultivation of some of the more important useful plants, the probability
that different varieties or elementary species have been the starting
points for different lines of culture, evidently becomes stronger.

Unfortunately, this historic evidence is scanty. The most interesting
facts are those concerning the use of apples by the Romans and by their
contemporaries of the Swiss and middle European lake-dwellings. Oswald
Heer has collected large numbers of the relics of this prehistoric
period. Apples were found in large quantities, ordinarily cut into
halves and with the signs of having been dried. Heer distinguished two
varieties, one with large and one with small fruits. The first about 3
and [75] the other about 1.5-2 cm. in diameter. Both are therefore very
small compared with our present ordinary varieties, but of the same
general size as the wild forms of the present day. Like these, they must
have been of a more woody and less fleshy tissue. They would scarcely
have been tasteful to us, but in ancient times no better varieties were
known and therefore no comparison was possible.

There is no evidence concerning the question, as to whether during the
periods mentioned apples were cultivated or only collected in the wild
state. The very large numbers which are found, have induced some writers
to believe in their culture, but then there is no reason why they should
not have been collected in quantity from wild shrubs. The main fact is
that the apple was not a uniform species in prehistoric times but showed
even then at least some amount of variability.

At the present day the wild apples are very rich in elementary species.
Those of Versailles are not the same as those of Belgium, and still
others are growing in England and in Germany. The botanical differences
derived from the blossoms and the leaves are slight, but the flavor,
size and shape of the fruits diverge widely. Two opinions have been
advanced to explain this high degree of variability, but [76] neither of
them conveys a real explanation; their aim is chiefly to support
different views as to the causes of variability, and the origin of
elementary species at large.

One opinion, advocated by De Candolle, Darwin and others, claims that
the varieties owe their origin to the direct influence of cultivation,
and that the corresponding forms found in the wild state, are not at all
original, but have escaped from cultivation and apparently become wild.
Of course this possibility cannot be denied, at least in any single
instance, but it seems too sweeping an assertion to make for the whole
range of observed forms.

The alternative theory is that of van Mons, the Belgian originator of
commercial varieties of apples, who has published his experiments in a
large work called "Arbres fruitiers ou Pomonomie belge." Most of the
more remarkable apples of the first half of the last century were
produced by van Mons, but his greatest merit is not the direct
production of a number of good varieties, but the foundation of the
method, by which new varieties may be obtained and improved.

According to van Mons, the production of a new variety consists chiefly
of two parts. The first is the discovery of a subspecies with new
desirable qualities. The second is the transformation [77] of the
original small and woody apple into a large, fleshy and palatable
variety. Subspecies, or what we now call elementary species were not
produced by man; nature alone creates new forms, as van Mons has it. He
examined with great care the wild apples of his country, and especially
those of the Ardennes, and found among them a number of species with
different flavors. For the flavor is the one great point, which must be
found ready in nature and which may be improved, but can never be
created by artificial selection. The numerous differences in flavor are
quite original; all of them may be found in the wild state and most of
them even in so limited a region as the Ardennes Mountains. Of course
van Mons preferred not to start from the wild types themselves, when the
same flavor could be met with in some cultivated variety. His general
method was, to search for a new flavor and to try to bring the bearer of
it up to the desired standard of size and edibility.

The latter improvement, though it always makes the impression of an
achievement, is only the last stone to be added to the building up of
the commercial value of the variety. Without it, the best flavored apple
remains a crab; with it, it becomes a conquest. According to the method
of van Mons it may be reached within [78] two or three generations, and
a man's life is wholly sufficient to produce in this way many new types
of the very best sorts, as van Mons himself has done. It is done in the
usual way, sowing on a large scale and selecting the best, which are in
their turn brought to an early maturation of their fruit by grafting,
because thereby the life from seed to seed may be reduced to a few
years.

Form, taste, color, flavor and other valuable marks of new varieties are
the products of nature, says van Mons, only texture, fleshiness and size
are added by man. And this is done in each new variety by the same
method and according to the same laws. The richness of the cultivated
apples of the present day was already present in the large range of
original wild elementary species, though unobserved and requiring
improvement.

An interesting proof of this principle is afforded by the experience of
Mr. Peter M. Gideon, as related by Bailey. Gideon sowed large quantities
of apple-seeds, and one seed produced a new and valuable variety called
by him the "Wealthy" apple. He first planted a bushel of apple-seeds,
and then every year, for nine years, planted enough seeds to produce a
thousand trees. At the end of ten years all seedlings had perished
except one hardy seedling [79] crab. This experiment was made in
Minnesota, and failed wholly. Then he bought a small lot of seeds of
apples and crab-apples in Maine and from these the "Wealthy" came. There
were only about fifty seeds in the lot of crab-apple seed which produced
the "Wealthy," but before this variety was obtained, more than a bushel
of seed had been sown. Chance afforded a species with an unknown taste;
but the growing of many thousands of seedlings of known varieties was
not the best means to get something really new.

Pears are more difficult to improve than apples. They often require six
or more generations to be brought from the wild woody state to the
ordinary edible condition. But the varieties each seem to have a
separate origin, as with apples, and the wide range of form and of taste
must have been present in the wild state, long before cultivation. Only
recently has the improvement of cherries, plums, currants and
gooseberries been undertaken with success by Mr. Burbank, and the
difference between the wild and cultivated forms has hitherto been very
small. All indications point to the existence, before the era of
cultivation, of larger or smaller numbers of elementary species.

The same holds good with many of the larger forage crops and other
plants of great industrial [80] value. Clover exhibits many varieties,
which have been cultivated indiscriminately, and often in motley
mixtures. The flower heads may be red or white, large or small,
cylindric or rounded, the leaves are broader or narrower, with or
without white spots of a curious pattern. They may be more or less hairy
and so forth. Even the seeds exhibit differences in size, shape or
color, and of late Martinet has shown, that by the simple means of
picking out seeds of the same pattern, pure strains of clover may be
obtained, which are of varying cultural value. In this way the best
subspecies or varieties may be sought out for separate cultivation. Even
the white spots on the leaflets have proved to be constant characters
corresponding with noticeable differences in yield.

Flax is another instance. It was already cultivated, or at least made
use of during the period of the lake-dwellers, but at that time it was a
species referred to as _Linum angustifolium_, and not the _Linum
usitatissimum_, which is our present day flax. There are now many
subspecies, elementary species, and varieties under cultivation. The
oldest of them is known as the "springing flax," in opposition to the
ordinary "threshing flax." It has capsules which open of themselves, in
order to disseminate the seeds, while the ordinary heads of the [81]
flax remain closed until the seeds are liberated by threshing. It seems
probable that the first form or _Linum crepitans_ might thrive in the
wild state as well as any other plant, while in the common species those
qualities are lacking which are required for a normal dissemination of
the seeds. White or blue flowers, high or dwarf stems, more or less
branching at the base and sundry other qualities distinguish the
varieties, aside from the special industrial difference of the fibres.
Even the life-history varies from annual and biennial, to perennial.

It would take us too long to consider other instances. It is well known
that corn, though considered as a single botanical species, is
represented by different subspecies and varieties in nearly every region
in which it is grown. Of course its history is unknown and it is
impossible to decide whether all the tall and dwarf forms, or starchy
and sweet varieties, dented or rounded kernels, and hundreds of others
are older than culture or have come into existence during historic
times, or as some assume, through the agency of man. But our main point
now is not the origin, but only the existence of constant and sharply
differentiated forms within botanical species. Nearly every cultivated
plant affords instances of such diversity. Some include a few types
only, while [82] others show, a large number of forms clearly separated
to a greater or lesser degree.

In some few instances it is obvious that this variability is of later
date than culture. The most conspicuous case is that of the coconut.
This valuable palm is found on nearly all tropical coasts, in America,
as well as in Asia, but in Africa and Australia there are many hundreds
of miles of shore line, where it is not found. Its importance is not at
all the same everywhere. On the shores and islands of the Indian Ocean
and the Malay Archipelago, man is chiefly dependent upon it, but in
America it is only of subordinate usefulness.

In connection with these facts, it abounds in subspecies and varieties
in the East Indian regions, but on the continent of America little
attention has as yet been given to its diverging qualities. In the
Malayan region it affords nearly all that is required by the
inhabitants. The value of its fruit as food, and the delicious beverage
which it yields, are well known. The fibrous rind is not less useful; it
is manufactured into a kind of cordage, mats and floor-cloths. An
excellent oil is obtained from the kernel by compression. The hard
covering of the stem is converted into drums and used in the
construction of huts; the lower part is so hard as to take on a
beautiful polish [83] when it resembles agate. Finally the unexpanded
terminal bud is a delicate article of food. Many other uses could be
mentioned, but these may suffice to indicate how closely the life of the
inhabitants is bound up with the culture of this palm, and how sharply,
in consequence, its qualities must have been watched by early man. Any
divergence from the ordinary type must have been noted; those which were
injurious must have been rejected, but the useful ones must have been
appreciated and propagated. In a word any degree of variability afforded
by nature must have been noticed and cultivated.

More than fifty different sorts of the coconut are described from the
Indian shores and islands, with distinct local and botanical names.
Miquel, who was one of the best systematists of tropical plants, of the
last century, described a large number of them, and since, more have
been added. Nearly all useful qualities vary in a higher or lesser
degree in the different varieties. The fibrous strands of the rind of
the nut are developed in some forms to such a length and strength as to
yield the industrial product known as the coir-fibre. Only three of them
are mentioned by Miquel that have this quality, the _Cocos nucifera
rutila_, _cupuliformis_ and _stupposa_. Among them the _rutila_ [84]
yields the best and most supple fibres, while those of the _stupposa_
are stiff and almost unbending.

The varieties also differ greatly in size, color, shape and quality, and
the trees have also peculiar characteristics. One variety exhibits
leaves which are nearly entire, the divisions being only imperfectly
separated, as often occurs in the very first leaves of the seedlings of
other varieties. The flavor of the flesh, oil and milk likewise yield
many good varietal marks.

In short, the coconut-palm comes under the general rule, that botanical
species are built up of a number of sharply distinguishable types, which
prove their constancy and relative independence by their wide
distribution in culture. In systematic works all these forms are called
varieties, and a closer investigation of their real systematic value has
not yet been made. But the question as to the origin of the varieties
and of the coconut itself has engrossed the attention of many botanists,
among whom are De Candolle in the middle of the last century, and Cook
at its close.

Both questions are closely connected. De Candolle claimed an Asiatic
origin for the whole species, while Cook's studies go to prove that its
original habitat is to be sought in the northern countries of South
America. Numerous [85] varieties are growing in Asia and have as yet not
been observed to occur in America, where the coconut is only of
subordinate importance, being one of many useful plants, and not the
only one relied upon by the natives for their subsistence. If therefore,
De Candolle's opinion is the right one, the question as to whether the
varieties are older or younger than the cultivated forms of the species,
must always remain obscure. But if the proofs of an American origin
should be forthcoming, the possibility, and even the probability that
the varieties are of later date than the beginning of their culture, and
have originated while in this condition must at once be granted. An
important point in the controversy is the manner in which the coconuts
were disseminated from shore to shore, from island to island. De
Candolle, Darwin and most of the European writers claim that the
dispersal was by natural agencies, such as ocean-currents. They point
out that the fibrous rind or husk would keep the fruits afloat, and
uninjured, for many days or even many weeks, while being carried from
one country to another in a manner that would explain their geographic
distribution. But the probability of the nuts being thrown upon the
strand, and far enough from the shore to find suitable conditions for
their germination, is a very small one. To insure [86] healthy and
vigorous seedlings the nuts must be fully ripe, after which planting
cannot be safely delayed for more than a few weeks. If kept too moist
the nuts rot. If once on the shore, and allowed to lie in the sun, they
become overheated and are thereby destroyed; if thrown in the shade of
other shrubs and trees, the seedlings do not find the required
conditions for a vigorous growth.

Some authors have taken the fibrous rind to be especially adapted to
transport by sea, but if this were so, this would argue that water is
the normal or at least the very frequent medium of dissemination, which
of course it is not. We may, claim with quite as much right that the
thick husk is necessary to enable the heavy fruit to drop from tall
trees with safety. But even for this purpose the protection is not
sufficient, as the nuts often suffer from falling to such a degree as to
be badly injured as to their germinating qualities. It is well known
that nuts, which are destined for propagation, are as a rule not allowed
to fall off, but are taken from the trees with great care.

Summing up his arguments, Cook concludes that there is little in the way
of known facts to support the poetic theory of the coconut palm dropping
its fruits into the sea to float away to barren islands and prepare them
for [87] human habitation. Shipwrecks might furnish a successful method
of launching viable coconuts, and such have no doubt sometimes
contributed to their distribution. But this assumption implies a
dissemination of the nuts by man, and if this principal fact is granted,
it is far more natural to believe in a conscious intelligent
dissemination.

The coconut is a cultivated tree. It may be met with in some spots
distant from human dwellings, but whenever such cases have been
subjected to a closer scrutiny, it appears that evidently, or at least
probably, huts had formerly existed in their neighborhood, but having
been destroyed by some accident, had left the palm trees uninjured. Even
in South America, where it may be found in forests at great distances
from the sea-shore, it is not at all certain that true native localities
occur, and it seems to be quite lost in its natural condition.

Granting the cultivated state of the palms as the only really important
one, and considering the impossibility or at least great improbability
of its dissemination by natural means, the distribution by man himself,
according to his wants, assumes the rank of an hypothesis fully adequate
to the explanation of all the facts concerning the life-history of the
tree.

We now have to inquire into the main question, [88] whether it is
probable that the coconut is of American or of Asiatic origin, leaving
aside the historic evidence which goes to prove that nothing is known
about the period in which its dissemination from one hemisphere to
another took place, we will now consider only the botanic and geographic
evidence, brought forward by Cook. He states that the whole family of
coconut-palms, consisting of about 20 genera and 200 species, are all
strictly American with the exception of the rather aberrant African
oilpalm, which has, however, an American relative referred to the same
genus. The coconut is the sole representative of this group which is
connected with Asia and the Malayan region, but there is no manifest
reason why other members of the same group could not have established
themselves there, and maintained an existence under conditions, which
are not at all unfavorable to them. The only obvious reason is the
assumption already made, that the distribution was brought about by man,
and thus only affected the species, chosen by him for cultivation. That
the coconut cannot have been imported from Asia into America seems to be
the most obvious conclusion from the arguments given. It should be
briefly noted, that it was kno