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PLANT HYBRIDIZATION
BEFORE MENDEL

London: Huntphrey Milford
Oxford University Press

PLANT HYBRIDIZATION
BEFORE MENDEL

H. F. ROBERTS

ASSISTANT PROFESSOR OF BOTANY
IN THE UNIVERSITY OF MANITOBA

PRINCETON
PRINCETON UNIVERSITY PRESS

1929

PRINTED AT THE PRINCETON UNIVERSITY PRESS
PRINCETON, NEW JERSEY, U.S.A.

PREFACE

IN the present work it is intended to present, in some fulness and
detail, all the significant results obtained in the field of plant-
hybridization, down to the discovery of Mendel's papers in
1900. The work of the early hybridists has never hitherto been
adequately analyzed and discussed as a whole. Attention has been
so concentrated upon Mendelian problems, that the contributions
of the precursors of the present scientific period in genetics have
been mostly overlooked, and not infrequently underestimated. To
bring these contributions out of oblivion, to present them in se-
quence, and in their relation to one another and to our present
knowledge, is the aim and purpose of the writer. In assembling
this material, the work of individual breeders upon the improve-
ment of some single species of plant, usually conducted entirely
from an empirical or purely practical standpoint, has generally
been omitted, those investigators only being included who have
contributed in some essential manner to the theory of fertilization
and hybridization in plants, and who have thereby laid a founda-
tion for the synthetic development of genetic theory. If Mendel's
papers themselves have been analyzed with unusual minuteness
and detail, it is because the writer feels that such a thoroughgoing
analysis is generally omitted in the current text-books on heredity,
and that in a work of this sort, intended to be historical rather
than genetic in character and also intended to be useful for refer-
ence purposes and to the general reader, it should be his duty to
make as complete an exposition as possible of each investigator's
contribution. It should be therefore^stated that in the presentation
of the Mendel material the details have been given with the same
thoroughness and simplicity as though the paper were being re-
viewed for the first time. It was thought by this means to be more
nearly possible to bring Mendel's actual work into its deserved
relief, too often obscured by brief statement. This will also suffice
to account for the simple and elementary re-statement of the

vi PREFACE

dominant-recessive character relations. For a discussion of the
extended development of theory and investigation based upon the
Mendelian discovery, reference must naturally be made to the va-
rious general text-books and handbooks in genetics, and to the
multitude of papers in the journals of biological science.

It has been necessary to make frequent use of the resources of
various libraries. Appreciation is particularly due the libraries of
the University of Chicago, Harvard, the Crerar Library of Chi-
cago, and the library of the Missouri Botanical Garden, for liberal
access to works of reference. Especial thanks are due the library
of the University of Manitoba for affording every possible means
for obtaining material, and for securing the loan of important
books.

The writer desires to express especial thanks to Dr. Geo. H.
Shull and Dr. E. G. Conklin of Princeton University, for most
thorough editorial reading given the manuscript in an earlier draft.
Their many constructive suggestions have been largely utilized.
For the manuscript in its present form, however, together with any
imperfections that may appear, the author is solely responsible.

The subject-matter of portions of the first four chapters has
appeared in past issues of the Journal of Heredity, to which
acknowledgments are due for the privilege of their reproduc-
tion in their present form, and for the use of the accompanying
illustrations. The Gartner material has appeared in part in the
American Naturalist. The portrait of Darwin is reproduced by
permission of the Cambridge University Press, from Volume I
of Professor Karl Pearson's "Life, Letters and Labours of Francis
Galton." The portraits of Mendel and of Bateson, and the
illustration of the Konigskloster in Briinn, are reproduced from
the Report of the Royal Horticultural Conference on genetics,
1906, by permission of the President and Council of the Royal
Horticultural Society. The portraits of MM. Louis and Henry
de Vilmorin are furnished by the courtesy of Messrs. Vilmorin
& Co. of Paris. The portrait of Galton is reproduced by per-
mission from Vol. II of Biometrika. A copy of Sir Thomas Mil-
lington's portrait was obtained by consent from the original in
the Royal College of Physicians in London. The copies of the
Assyrian bas-reliefs in Plates VIII, IX, and X, are photographed

PREFACE vii

from the originals in the British Museum, Nimrud Gallery, Nos.
24, 40, and 2. The portrait of Linnaeus (Plate XV) is from Plate
VIll, opp. p. 36, of the collection entitled "Linneportratt vid
Uppsala A Universitets Vagnar af Tycho TuUberg, Stockholm,
1907." The younger portrait of Camerarius (Plate XIl) is fur-
nished by Professor E. Lehmann of the University of Tubingen,
from the oil painting in the library of the University. The por-
trait of Naudin was kindly obtained by Professor Georges Poir-
ault, of the Villa Thuret, Cap d'Antibes, France, and that of
Godron by the Doyen of the Faculte des Sciences of the Univer-
sity of Nancy. To Professor E. Baur of Berlin, acknowledgments
are due for valuable biographical material on Sprengel and Focke,
and to Professor Correns for a portrait of Wichura. To Professors
De Vries, Correns and von Tschermak are due especial thanks for
kindly furnishing full accounts of their individual discoveries of
the Mendel papers and the Mendelian theory. In conclusion, with
regard to the form of the present book, which may be criticized
for its considerable volume of quoted material, it should be said
that two ways were open; — simply to digest the material and
present it without quotation except in very significant instances ; or
to give liberal extracts from the works themselves, in order to sub-
serve the purposes of research to those desiring access to the
actual corpus of material embodied in the works of the early hy-
bridists. In some of the Nageli and Kolreuter material, for ex-
ample, the former method was followed, but in general the latter
was chosen, even at the risk of creating in part a volume of ex-
tracts. It was thought that the real ends of science would be best
served in a book of this kind by making it available directly as
research material, rather than by sacrificing those ends to the
aims of authorship. Hence the resulting rather cumbrous form
of the material, which could have been otherwise displayed if the
former method had been exclusively followed. It is hoped, how-
ever, that the purpose of the book" may be allowed to apologize
for its resultant form.

H. F. Roberts.

UNIVERSITY OF MANITOBA.
AUGUST 2, 1928.

CONTENTS

CHAPTER I

5
6

Early experiments in plant breeding 1

Date culture in early Babylonia and Assyria i

The relation of the date palm to plant breeding 4

Variation and selection of the date 7

The discovery of sex in plants 9

Camerarius 12

Linnaeus 15

CHAPTER n

8. Kolreuter 34

CHAPTER in

9. Miscellaneous experiments regarding sex in plants 62

10. Gleditsch's palm pollination experiments 70

11. Christian Konrad Sprengel 78

CHAPTER IV

12. Thomas Andrew Knight 85

13. William Herbert 94

14. John Goss and Alexander Seton 102

15. The experiments of Thomas Laxton 104

16. The work of Patrick Shirreff llO

CHAPTER V

17. The experiments of Sageret 120

18. Godron and Naudin on hybridization 123

19. Ve riot's memoir on the breeding of plants 136

20. The work of the Vilmorins 143

21. Lecoq's memoir on hybridization 154

4:.^H5a

X CONTENTS

CHAPTER VI

22. Wiegmann's experiments l6o

23. The work of Carl Friedrich von Gartner 164

24. Wichura and the hybridization of willows 178
25". Kegel on hybridization 183

26. Carl von Nageli and the hybrid question 183

27. Treatise of W. O. Focke 204

28. The Hoffmann Mendel citations 216

CHAPTER VII

29. Darwin's contribution to the theory of hybrids 221

CHAPTER vin

30. Sir Francis Galton's investigations in heredity 241

CHAPTER IX

31. Miscellaneous investigations on the histological

structure of hybrids : 260

a. Henslow 260

h. Macfarlane 262

c. Wilson 275

d. Darbishire 276

32. Spillman, Mendelian results with wheat, prior to 1900 276

CHAPTER X

33. The investigation of Gregor Mendel 286

CHAPTER XI

34. The discovery of Mendel's papers : 320

a. Hugo De Vries 324

h. C. Correns 335

c. E. von Tschermak 343

CHAPTER XII

33". The contribution of William Bateson 359

Index 367

ILLUSTRATIONS

Plate I

Date palms in Mesopotamia l

Plate II

Flowers of the date 2

Plate III

Date inflorescences 3

Plate IV

Young date tree in fruit 4

Plate V

Fruiting branch of the date 5

Plate VI

Demonstration by Arabs of the pollination of the date 6

Plate VII

Demonstration by Arabs of the polltnatiofi of the date 7

Plate VIII

Figure of Ashur-nasir-pal attended by winged
mythological being 8

Plate IX

Assyrian bas-relief of priest 9

Plate X

Two figures of Ashur-nasir-pal attended by priests 10

Plate XI

Rudolph Jacob Camerarius 13

xii ILLUSTRATIONS

Plate XII

Camerarius, younger portrait 14

Plate XIII

Title-page of the extract from Camerarius' ''De Sexu
Plantarum Epistold" 15

Plate XIV

Title-page of Valentiris ''Res pons oria' to the Camer-
arius Epistola 16

Plate XV

Carl von Linne 17

Plate XVI

Title-page of the ''Disquisitio de Sexu Plantarum'^

of Linnaeus 18

Plate XVII

Title-page of the ''Plantae Hybridae" of Johannes
Haartman 25*

Plate XVIII

Linnaeus' Hybrid^ "Veronica maritima X Verbena
officinalis'' 27

Plate XIX

J. G. Kblreuter 3^

Plate XX

Sir Thomas Milling ton 63

Plate XXI

Philip Miller 67

Plate XXII

James Logan 69

Plate XXIII

Title-page of SprengeVs ''Das Entdeckte Geheimmss

der Natur" 79

ILLUSTRATIONS xiii

Plate XXIV

Thomas Andrew Knight 86

Plate XXV

Patrick Shirreff ill

Plate XXVI

D. A. Godron , 124

Plate XXVII

Charles Naudin 125

Plate XXVIII

Louis Leveque de Vilmorin 145

Plate XXIX

Henry Leveque de Vilmorin 146

Plate XXX

Henri Lecoq 152

Plate XXXI

C. F. von Gartner 165

Plate XXXII

Village of Calzv, in Wurtemberg^ home of C. F. von
Gartner 166

Plate XXXUI

Marketplace in Calzu 166

Plate XXXIV

Present site in Calzu of a portion of the former
experimental garden of C. F. von Gartner 167

Plate XXXV

Max Ernest Wichura 179

Plate XXXVI

Carl von Ndgeli 184

xiv ILLUSTRATIONS

Plate XXXVII

W. O. Focke 205

Plate XXXVIII

Hermann Hoffmann 2,17

Plate XXXIX

' Charles Darwin 2,22

Plate XL

Sir Francis Gallon 242

Plate XLI

Digitalis lutea X purpurea; flowernig organs and tis-
sues of parents and F^ hybrid, by J. S. Henslow 261

Plate XLII

Gregor Mendel 287

Plate XLI 1 1

The Augustinian Cloister at Brilnn 288

Plate XLIV

Hugo De Vries 3^2

Plate XLV

C. Correns 33^

Plate XLVI

E. von Tschermak 344

Plate XLVI I

William Bateson 3^0

Plate XLVI 1 1

Facsimile of letter of Mendel to Ndgeli, with

signature 3^2

PLANT HYBRIDIZATION
BEFORE MENDEL

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tci^^

Plate I. Date palms in Mesopotamia.

CHAPTER I

THE EARLIEST DISCOVERIES REGARDING SEX IN PLANTS

1. Early Experiments in Plant Breeding.

A FULL discussion of the history of the views, opinions, and
discoveries regarding sex in plants is reserved for a later
publication. On this account, therefore, the present ref-
erences to the subject will be necessarily brief.

Exactly where or when man first began to practise the cultiva-
tion of plants and to bring them into domestication is not known.
It is certain however, that one of the earliest homes of civilized
man was in the lower basin of the Tigris and Euphrates rivers
in southwestern Asia, today known as Iraq, the site of the tradi-
tional "Garden of Eden."

From four to six thousand years before the present era, and at
least fifteen hundred years before the days of the Jewish patri-
arch Abraham, this region was occupied by an already ancient,
orderly and settled people, possessing both cultivated plants and
domestic animals. Indeed, there is little reason to doubt that the
low alluvial plain fed by the "waters of Babylon" was the scene
of one of the first of civilized man's attempts at the improvement
of plants, for it is known that the cultivation of the date palm
was being carried on in this region during the very earliest times.

2. Date Culture in Ancient Babylonia and Assyria.

The history of the date palm typifies better than that of almost
any other plant, man's relation to the plant world as a moulder
of its cultivated forms.

The fact of the culture of dates in Mesopotamia in ancient
times is demonstrated by Babylonian and Assyrian monuments,
and was recorded by several of the early Greek historians ; the
monuments show not only the fact of the culture of the date, but
even plainly represent the process of hand-pollination.

Plate II. Flowers of the date. Right (open cluster), staminate ; left, pistillate. From
U.S. Department of Agriculture, Bureau of Plant Industry, Bull. 53, Plate 7, Fig. 3.

PLANT HYBRIDIZATION BEFORE MENDEL 3

In an Assyrian bas-relief, Ashurbanipal, the Sardanapalus of
the Greeks {circa 650 B.C.), is represented in his garden, with
fruiting garlands of the grape overhead, while to the rear a date
palm is represented laden with fruit.

The tremendous economic value of this remarkable tree, even

Plate III. Date inflorescences. Left, staminate inflorescence just emerging from the
sheath ; right (3 figures), pistillate inflorescence in different stages. From U.S. Depart-
ment of Agriculture, Bureau of Plant Industry, Bull. 53, Plate 7, Figs. 1 and 2.

in early times, was attested by a Persian hymn, referred to by
Strabo (13),^ which is reported as having mentioned three hun-
dred and sixty uses for the plant. Later, in the thirteenth century,
the celebrated traveller, Marco Polo, speaks of a "city called
Bastra (modern Busreh), surrounded by woods in which are
grown the best dates in the world."

1 Numbers in parentheses refer to the bibliographical list to be found
at the end of each chapter.

4 PLANT HYBRIDIZATION BEFORE MENDEL

3. The Relation of the Date Palm to Plant Breeding.

It had probably always been recognized, since animals were
first extensively domesticated, that the fact of sex lay at the basis
of whatever improvement in their characters man could bring

Plate IV. A young date tree in fruit. U.S. Department of Agriculture, Bureau of
Plant Industry, Bull. 271, Plate 9, Fig. 2.

about, for the reason that, in animals, "breeding" has always
meant the use of superior breeding animals (usually superior
males) in crossing. In plants, however, the fact of sex is less
evident than in animals, partly because in most plants the sexes
are not separated. In the date palm we have at the same time a
plant of great economic value in certain regions, and one in which
the sexes exist separately as in the higher animals. It therefore

PLANT HYBRIDIZATION BEFORE MENDEL 5

came to be recognized, from very early times, that the date trees
were of two kinds, sterile and fruit-bearing, in other words,
"male" and "female," and that the product of a sterile "male"

Plate V. Fruiting branch of the date ; Deglet Nur variety, showing the fruiting stalk
or peduncle (Arabic "Sobata'^), and the individual bearing-strands or pedicels, known
collectively (Arabic) as the "Shamrokh." U.S. Depanmtnt of AgricuLure, Bureau of
Plant Industry, Bull. 223, Fig. 12.

tree was needed in order to ensure the bearing of fruit by a fertile
"female" tree.

Kazwini (6), an Arabic writer on natural history, says of the
date : "It is created out of the same substance as Adam, and is
the only tree that is artificially fertilized."

The seeds of the date palm produce in about equal numbers
male and female trees. The female trees are wind-pollinated, and
therefore under natural wild conditions there would easily be
enough male trees to fertilize them. Under cultivation, however,
the growing of such a large proportion of non-fruiting or sterile
trees would be a very wasteful use of the land, and we find that
quite early (probably as early as Babylonian and Assyrian times)

PLANT HYBRIDIZATION BEFORE MENDEL

it was discovered that the pollen from a small number of male
trees could be employed to fertilize a considerable number of
female trees, by substituting hand-pollination for the natural

Plate VI. Demonstration by Arabs of the pollination of the date. Insertion of a sprig
of the staminate flowers in the midst of the pistillate cluster. U.S. Department of
Agriculture, Bureau of Plant Industry, Bull. 53, Plate 8, Fig. 3.

method. At the present time, according to Swingle (14), the pro-
portion used in planting is about one male to one hundred female
trees.

PLANT HYBRIDIZATION BEFORE MENDEL 7

4. Variation and Selection of the Date.

It was soon learned that, when the seeds from the fruits thus
obtained by fertilization w^ere planted, the offspring could no more
be depended upon to bear fruits like the original, than can the
seedlings of budded peaches, apples or pears. As a matter of fact,

Plate VII. Demonstration by Arabs of the pollination of the date. Clusters of the
pistillate flowers being tied together to hold the staminate flowers in place. U.S. De-
partment of Agriculture, Bureau of Plant Industry, Bull. 53, Plate 8, Fig. 4.

PLANT HYBRIDIZATION BEFORE MENDEL

the seedlings coming from any given variety of date show a very
wide range of variation, and it is said that the original parent
type seldom re-appears among the seedlings (14).

This diversity of type among seedling dates has led to the es-

^■^ >>*** l$yiJ

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^jdW*

Plate VIII. Figure of Ashur-nasir-pal, King of Assyria, 883-859 B.C., attended by a winged
mythological being carrying pollination basket in left hand, and in the right the
staminate inflorescence of the date palm — a ceremonial act. Slab 24, Nimrud Gallery,
British Museum.

tablishment of a great number of varieties in cultivation. From
four oases in the Sahara alone over four hundred distinct varieties
of dates are reported, which differ greatly from one another in
many cases, in the size, shape, and flavor of the fruits.

It is possible to see, therefore, that through the medium of the
date palm, at a very early period, the fact was learned of the

PLANT HYBRIDIZATION BEFORE MENDEL 9

existence of variation in cultivated plants, a fact which renders
selection possible, and in a manner also there was learned the fact
of the existence of sex in plants, upon which "plant breeding" is
based.

5. The Discovery of Sex in Plants.

We have seen that the Assyrians and Babylonians understood

: '*m':^f^i^:^fiSffif^^f^.&&^<iKi-^yyy.

j*9»*"****

/"'

Plate IX. Assyrian bas-relief. Priest wearing winged apparel and a bird-headed mask,
with pollination basket in left hand and staminate inflorescence of date palm in the
right. Slab 40, Nimrud Gallery, British Museum.

PLANT HYBRIDIZATION BEFORE MENDEL ii

that date palms were of two sorts, male and female, and that they
apparently utilized this knowledge in a practical way, by resort-
ing to the artificial pollination of the female trees, in order to
make them hear more abundantly. This would naturally give rise
to some sort of a conception of sex in the plant as a kind of
analogy, but in the absence of evidence of the means and processes
of fecundation the conception of plant-sex would be apt to re-
main long a poetic idea rather than a scientific conclusion. The
Arabs, at all events, have continued the practice of the pollination
of the palm uninterruptedly down to the present (12b) and, indeed,
they seem to have had an idea that the date palm possessed sex
somewhat in the same sense in which it exists in the animal king-
dom. The Arabic writer Kazwini (circa a.d. 1283), to whom refer-
ence has already been made, says plainly in the book entitled
"Of the Marvels of Nature, and of the Singularities of Created
Things" ;

"The date has a striking resemblance to man, through the beauty of
its erect and slender figure, its division into two distinct s^xes, and the
property, which is peculiar to it, of being fecundated by a sort of
union."

However, the lesson which the date palm might have been sup-
posed to teach, namely, that plants possess sex and that breeding
can be conducted with them as with animals, appears to have been
lost sight of. Even in those regions where the date was habitually
grown, the idea which the long-continued practice of artificial pol-
lination might have suggested — that it was possible to breed
and improve other plants in like manner — appears never to have
arisen. It would perhaps be thought that the ancient Babylonians,
having learned the art of artificial crossing in the case of one
plant, would have applied the same process to others. The reason
for their failure to do so, however, is explainable. No other eco-
nomic plants with which they came into contact in their fields
were similarly dioecious. They did not, for example, chance to
possess an annual species like Indian corn, in which, on one and
the same plant, the male and female flowers are in separate in-
florescences, in which the pollination is a conspicuous fact, and
in which crossing not only can be seen to be continually taking
place in nature, but likewise can easily be carried out by artificial
means. It is to be remembered that the artificial pollination of the

12 PLANT HYBRIDIZATION BEFORE MENDEL

date was practised solely for the production of the fruit and not
for the production of seeds or for the purpose of breeding the
plant. The breeding of new plants remained a mere matter of
chance and was due to the selection of superior bearing trees
where they occurred. It is otherwise possible that, if annual
grain-plants of the dioecious type had been accessible, further
advance might have been made in plant breeding, even at an
early period. As a matter of fact however, no lesson was learned
from the example of the date palm. The book was closed — and
the land of Babylonia, where those whom we may call the first
plant breeders lived, became the desert which it remains to this
day. Literally, in the words of the Prophet Jeremiah, "Her cities
are a desolation, a dry land, and a wilderness."

6. The First European Investigations on Plant Sex. Camerarius
(1665-1721).

On the 25th of August, 1694, Rudolph Jakob Camerer, Pro-
fessor of Natural Philosophy in the University of Tubingen, bet-
ter known under the Latinized name of Camerarius, published a
memoir in the form of a letter to a colleague. Professor Michael
Bernard Valentin, of the University of Giessen.

This extraordinary "letter" is entitled "De Sexu Plantarum
Epistola" (2). It recounts at length the knowledge, slender enough
though it was, on the subject which existed up to his time, gives
a description of Camerarius' own experimental work, and consti-
tutes the first contribution in the form of an actual scientific in-
vestigation into the question of the existence of sex in plants.

The Greek and Roman writers on natural history, Aristotle (1),
Herodotus (5), Pliny (11), Theophrastus (15), and others, had
commented on the supposed existence of the sexes in plants, even
definitely citing the case of the date palm ; but the texts report
no actual experiments for determining the facts. This latter,
therefore, was the contribution of Camerarius.

Camerarius appears to have been the first botanist to discover,
by actual experimentation, that the pollen is indispensable to
fertilization, and that the pollen-producing flowers or plants are
therefore male, and the seed-bearing plants female. The experi-
ments were conducted with Mercurialis, spinach, and hemp, all
of which are dioecious, and with Indian corn or maize. Camer-
arius was likewise the first investigator to discover, in the case

PLANT HYBRIDIZATION BEFORE MENDEL

of maize, two hundred years after its introduction into Europe,
the fact that on removing the pollen-bearing flowers from the
staminate inflorescence of an isolated plant the seeds remained
unfertilized.

Plate XI. Rudolph Jacob Camerarius, 1665-1721. From Ostwald's "Klassiker der exak-
ten Wissenschaften." No. 105.

14 PLANT HYBRIDIZATION BEFORE MENDEL

The results obtained by Camerarius with the species mentioned

enabled him to deduce the following conclusion regarding sex in

plants :

"They behave indeed to each other as male and female, and are other-
wise not different from one another. They are thus distinguished with
respect to sex, and this is not to be understood as it is ordinarily done,
as a sort of comparison, analogy, or figure of speech, but it is to be
taken actually and literally as such." (2c, p. 28.)

Plate XII. R. J. Camerarius. Younger portrait. From an oil painting in the library of

the University of Tubingen.

PLANT HYBRIDIZATION BEFORE MENDEL 15

Camerarius himself did not fail to sense the possibilities latent
in the field of hybridization, as the following comment indicates
(2c, p. 49) :

"The difRcult question, which is also a new one, is whether a female
plant can be fertilized by a male of another kind, the female hemp by
the male hops ; the castor bean from which one has removed the stami-
nate flowers, through pollination with the pollen of Turkish wheat

BiLD. mDOlPHi J MOB I CAMEKAMH,

Afel D, if P,P^

Acad. &fareo - Leopold N. C* Colleg* d* Hect» IL

Ji% a MICHAELEM BERNARDUM \'ALENTIN%

^ Prof Giijfimm ijCmiqf. JnESSJiUAi '

SEXU PLANTARUM

p I <\Tn I A

Plate XIII. Title-page of the extract from Camerarius' "De Sexu Plantarum Epistola,"
as printed by Valentin in the Appendix to the "Ephemerides" of the "Academia
Caesareo-Leopoldina," 1696.

(maize) ; and whether, and in what degree altered, a seedling will arise
therefrom."

In this sentence is embodied, though in somewhat odd fashion,
an actual scientific conception in the matter, although no experi-
ments on the subject seem to have been attempted by the writer.
In this brief paragraph is perhaps revealed, however, the sugges-
tion of a new era of scientific investigation.

It was, nevertheless, more than fifty years before Camerarius'
investigations upon sex in plants received substantial recognition,
and before the first recorded instance of an actual experiment in
hybridization.

7. Linnaeus. (1707-1778.)

The relation of Linnaeus to hybridization and the question of
sex in plants deserves to be discussed for the sake of the point of

PLANT HYBRIDIZATION BEFORE MENDEL

view which he expresses regarding the work of Camerarius, as
well as for his own contribution to the subject.

In 1759, the Imperial Academy of Sciences at St. Petersburg
published an offer of a prize for the determination of the problem
of sex in the plant kingdom, as follows:

"Sexum plantarum argumentis et experimentis novis, praeter adhuc

Dn. D. MiCHAELiS BERNHARDI
rALENTiNl

RESPONSORIA

Dn. D. RUDOLPH! JACOBI

CAMERARIl

.ANTARUM.

Plate XIV. Title-page of the "Responsoria" of Valentin to the Camerarius Epistola.
Appendix to the "Ephemerides" of the "Academia Caesareo-Leopoldina," 1696.

jam cognita, vel corroborare, vel impugnare, praemissa expositione his-
torica et physica omnium plantae partium, quae aliquid ad foecunda-
tionem et perfectionem seminis et fructus conferre creduntur."

The essay of Linnaeus, entitled "Disquisitio de sexu plan-
tarum," was awarded the prize on September 6, 1760.

Concerning this work, it is stated, in the Praefatio to the "Fun-
damenta Botanica" published under the editorship of J. E. Gilibert
in 1786 (p. viii) :

"egregius autor Linnaeus vere novis, variisque experimentis potentiam
antherarum seu testiculorum plantae pro foecundatione germinum stabi-
lavit, addit quaedam de hybridis, plurima de motibus voluntariis partium
floris."

"To say exactly," Linnaeus remarks, "who first came upon the
sex of plants, would be a thing of great difficulty, and of no use."
(8c, p. 102.)

PLANT HYBRIDIZATION BEFORE MENDEL

The growth of the concept Is taken as analogous to the growth
of a river, by small, insensible degrees. The fact is alluded to,
that the ancient cultivators of palms, figs, and the pistacio (dioe-
cious plants) attained to a certain knowledge of the fact, to the
extent that it was found necessary to suspend the male flowers
over the females, if fruit was to be obtained. It is noted by Lin-
naeus, that after the Renaissance, and even in the seventeenth
century, botanists in general adhered to the "pristine ignorance"

Plate XV. Carl von Linne, 1707-1778.

IX.

CAR. LINN. EI

Equ. &: Archiuir. ll'cg. £:c.

DISQUISJTIO

SEXU PLANTARUM

ab Acaciemia Imperiali Scientiarum Petiopolitana

prsmio (*) omaca

an. 1760. d. 6. Septeoibr.
C U -M A N N O T A T I O X I B U S

D. JACOBl EDUARDI SMITH

P. M. AUG. BnOUSSONET.

m I ' ' I...IHIIIII II m

Fauiam exteiidere fattis.

Scxus plantarum andquillimos jam iiatiirs fcru-
tatorcs latere non potuit, ab hujus rero mv'i
pliilnnophi.*? palpari eciam pofljt, opcrtct. Hoc
cnim pha^nomeiion adeo m omnibus plantis nacura
IpedatKium prxbet, uc nulJam prorliis vcgetabile
CO carerc pacintur.

('5'^ Q{i;\' proMciua: St\x:i:n p'arJaX'nm £lrv;ii'}h'vi:; f\' fx-
■fteritiicniJ.'i novis^ -u-aier u.^}i:tr jatn r'')if;w-,: ^ -,/ carro-
iufnire, rrl ■.'niniyjmfc. pfaiuija -v :■ / .,,,., ,. ,U)rka f^
phijiiiit onfiifiiui pinntoe pr,i-itniii , tu-ig (Viou: i aa fijcatU'
dationan & pcr/trY/oner?/ Jrnrirs - ■' •, /■,'?;, ,v ivn/errfi
creduuiur^ m unn. 175^. pro prxiniu pru|.ulucrac.

Plate XVI. Title-page of the "Disquisitio de Sexu Plantarum of Lin-
naeus. Prize essay of the Imperial .Academy of the Sciences at St. Peters-
burg, 1760.

PLANT HYBRIDIZATION BEFORE MENDEL 19

regarding sex in plants, although Ray recognized the different
sexes in such dioecious plants as Cannabis^ Urtica, Mercurialis,
Humulus, etc., while Tournefort, on the contrary, followed the
error of the ancients. Millington is referred to, in the words:

"they report him to have been the first true discoverer of this doctrine,
if indeed it is permissible to call him the discoverer, who perceived some-
thing, but did not teach it in public writing." (8c, p. 103.)

It is of especial interest to note Linnaeus' opinion of Camera-
rius' work, briefly expressed as follows :

"Rud. Jac. Camerarius and others explained very many things, but no
one better than Vaillant, that great botanist of the French, who, in an
academic address, edited by Boerhaave, showed himself to have accurately
known the matter, although he did not demonstrate it with arguments."
(lb., p. 103.)

It is of interest to note parenthetically, in the "Sponsalia Plan-
tarum" of Wahlbom (8a), one of the pupils of Linnaeus, the
following statement, also made with regard to Camerarius:

"1695, Rudolphus Jacobus Camerarius, in the 'Epistola de sexu plan-
tarum,' Tubingen, first clearly demonstrated sex and generation, although
he was himself not devoid of doubt concerning this truth, which moved
him to the experiments which he made with Cannabis." (p. 219.)

Of Vaillant, Wahlbom also states, in the same connection, as
follows :

"1718. Sebastianus Vaillantius ; discourse concerning the structure of
flowers (Lugdun. Batav.). He first truly discerned the sexes of plants, and
by many observations placed beyond doubt this mystery of nature, which
seemed to all before paradoxical and absurd."

It is, indeed, surprising to find the preference accorded, by a
mind like that of Linnaeus, or rather, speaking literally, by Lin-
naeus and one of his pupils, to the rhetorical discussion of Vail-
lant over the scientific experimentation of Camerarius. Wahlbom,
as a pupil of Linnaeus, probably reflects the latter's view in the
matter.

Returning to Linnaeus' "De sexu plantarum":

"There is," he says, "in certain plants a true difference of sex; these
proceed from the seeds of one mother; but certain ones in their flowers
show stamens without pistils, and so are rightly called males; others,
pistils without stamens, and by right are called females ; and this by
so constant a law, that never any plant is seen to have borne female
flowers, unless other staminiferous flowers were found, either in the
same plant, or in different plants of the same species, and versa vice."
(ib., p. 112.)

20 PLANT HYBRIDIZATION BEFORE MENDEL

Linnaeus contends against the view of Morland and others
that the pollen itself enters the stigma, descends through the style.
and enters the ovary. This concludes the theoretical portion of
the dissertation.

The first experiment which Linnaeus records consisted in re-
moving, "circa vesperam mense Augusti," all the stamens from
three flowers of Mirabilis longiflora, the other flowers having been
destroyed. The flowers emasculated were pollinated with pollen
from Mirahilis jalapa. The ovules grew but did not mature,
(p. 114.)

"Another evening," he says, "I instituted the same experiment, but
pollinated (irrorabam) with the anthers of its own species, and all the
seeds matured." (8c, p. 114.)

The next experiment is reported as follows :

"in the month of January of this year Antholyza cunonia bloomed in
the window of my room, in an earthen pot, but bore no fruit, because
the air, enclosed within the walls, was unable to carry the pollen to the
stigma. On a certain day about noon, seeing the stigma absolutely moist,
I removed an anther with slender forceps, and lightly rubbed it over
one of the expanded portions of the stigmas. The spike of flowers re-
mained for eight or ten days, a fruit developing in that flower from
which I had previously removed the anther, and swelling to the magni-
tude of a bean. This therefore I opened, and saw, in but one of the three
cavities, many seeds developing, while the remaining two loculi were
absolutely void." {ib., p. 115.)

In the following April, Linnaeus sowed seeds of Can?iabis in
two vessels grown by the window in two different rooms. In one
of the vessels, the male and female plants were allowed to grow
flowers and bear fruit, which matured in July. The seeds ob-
tained, on being planted, germinated in twelve days. In the other
of the vessels, all the male plants were removed, at the age when
it was possible to distinguish "the antheriferous males" from the
"pistilliferous females." The female plants put forth flowers,
the pistils of which lasted unfertilized as long as was required in
the other vessel for the fruits to come to maturity, when the
pistils, in a quite different manner, immediately withered, after
the males had entirely shed their pollen. The unfertilized plants
retained their pistils in a green, vegetative condition, and did not
wither until when,

"after a long time, they were exposed to the afHatus of the male pollen.
Although the virgin plants produced large calices, these were empty of
living seeds. . . . From which I am quite sure that for the hemp deprived

PLANT HYBRIDIZATION BEFORE MENDEL 21

of the male to have borne seeds afterwards, as authors have reported to
us, was not effected except by the aid of pollen brought by the wind from
somewhere. For no experiment is easier than this ; none can be more
decisive for demonstrating the generation of plants." {ib., p. 116.)

Datisca cannabina, which had grown for ten years in Linnaeus'
botanical garden and had been propagated by perennial roots,
produced many flowers, but all females, and hence abortive.

(p. 48.)

New seeds were obtained from Paris, and a few tested. These

again gave only females, producing flowers without fruits. Fi-
nally, in 1757, seeds were again obtained, from which some of the
plants came males, flowering in 1758. These were transported to
a place as remote as possible from the female plants. When the
male flowers were at the point of discharging their pollen, the
inflorescence was shaken over a sheet of paper "until the sheet
was nearly covered with the yellow pollen." This was placed in-
verted over the blossoming female flowers. A nocturnal frost
in this year injured the Datiscas along with other plants; but
investigation of the plant, on the flowers of which the pollen had
been scattered, showed the rudiments of seeds, whereas in the
others not pollinated theie appeared no vestiges of seeds, {ib.,
p. 119.)

Jatro'hka urens is reoorted upon as follows: This plant is dioe-
cious. The two sexes flowered annually in the hothouse, but the
females preceded the males, dropping their petals or their flow-
ers, eight days before the appearance of the male flowers. Thus,
up to the year 1752, no fruit of Jatropha was obtained. In this
year the male flowers were in a flourishing condition on a taller
tree, when another small Jatropha set in a pot in the garden began
to produce female flowers. This female plant was then set under
the staminate tree. This pistillate tree consequently bore seeds
which, on being sowed, germinated. On another occasion, pollen
of Jatropha which had been kept for four to six weeks was used
for pollinating three pistillate flowers which had expanded in
the meantime. "These three females turned out to be fruit-
bearing, but all the rest in the same corymb became abortive."
{lb., p. 120.)

This practically concludes the record of Linnaeus' own direct
experimental contribution to the matter of sex in plants.

The pollination of the Gleditsch palm in Berlin with the pollen

22 PLANT HYBRIDIZATION BEFORE MENDEL

from Leipzig is evidently referred to on page 124, although the
species is wrongly given as Phoenix dactylifera. Kaempfer's re-
port upon the custom of hand pollination of the date in eastern
countries is referred to in the following words :

"Kaempfer recently reported that it is necessary that oriental peoples,
subsisting upon the yield of the palms and the true Lotophagi, trans-
port the male trees to the neighborhood of the females, if they look for
fruit." (p. 125.)

Linnaeus concludes by giving an account of four hybrid plants
known to have originated in his time :

"Tres ego, vel quatuor, veras, plantas hybridas meo primum extitisse
tempore his oculis vidi, quas ordine enumerabo." (p. 125.)

The Veronica maritima 5 X Verbena officinalis S (see p. 27
below) is referred to as resembling the female parent in the
fructification, the male parent in the leaves ("fructificatione ma-
trem tota quanta refert, foliis patrem"). (p. 126.)

Omitting the references to a Delphinium and a Hieracium hy-
brid, both of which occurred spontaneously, the case should be
noted of the hybrid Tragopogon^ resulting from a cross made
by Linnaeus between Tragopogon pratense 5 X Tragopogon por-
rifolius $ . The history of this hybrid, of which seeds were sent
to the St. Petersburg Academy at the same time as the disserta-
tion, is as follows :

Linnaeus states that he made the cross mentioned above in
'757' "^^ areola horti," where he had planted the two species.

"I obtained Tragopogon hybridum two years ago about autumn, in a
small enclosure of the garden, where I had planted Tragopogon
pratense and Tragopogon porrifolius, but the winter supervening de-
stroyed the seeds. Early the following year, when Tragopogon pratense
flowered, I rubbed off the pollen early in the morning, and at about
eight in the morning I sprinkled the pistils with pollen from Tragopogon
porrifolius and marked the calices with a thread bound around them.
From these, towards autumn, I collected the mature seeds, and sowed
them in a separate place, where they germinated, and in this year 1759-
gave purple flowers with yellow bases, the seeds of which I now send."
(pp. 126-7.)

Linnaeus finally concludes with the naive observation:

"I do not know whether any other experiment would show generation
more certainly than this one itself," (p. 127.)

Hybrid fertilization thus appears to Linnaeus as a new field
opened up to botanists,

PLANT HYBRIDIZATION BEFORE MENDEL 23

"in which, with the pollen of diverse plants upon diverse females . . .
they may attempt to effect new species of vegetables. And if I observe
this to be not displeasing, the more will my mind be aroused, for that
period of life which is left to me, to be consecrated to these experi-
ments, which recommend themselves both in virtue of their attractive-
ness and by their great usefulness. For, led by many reasons, I am of
the opinion that the many and prominent varieties of plants in use in
the kitchen have been produced by that kind of generation, such as
the numerous Brassicas, Lactucas, etc., and therefore have not been
changed by their location. Wherefore I am unable to have confidence in
that rule which holds that all varieties arise from the diverse nature of
the soil ; for if it were true, plants indeed, when they are changed to
new places, would recover their pristine aspect." (p. 129.)

"It is impossible to doubt that there are new species produced by hybrid
generation. From all these things, we learn that the hybrid is brought
forth, as to the medullary substance or the internal plant or fructifica-
tion as the exact image of the mother, but as to its leaves and other
external parts it is as that of the father. These considerations, there-
fore, lay down a new foundation for the students of nature, to which
many things contribute. For thence it appears to follow, that the many
species of plants in the same genus in the beginning could not have
been otherwise than one plant, and have arisen from this hybrid genera-
tion." (pp. 127-8.)

In a dissertation entitled "Fundamentum fructificationis," Octo-
ber 16, 1762, appearing as No. 8, in the "Fundamenta Botanica"
(Vol. 1, pp. 169-214) 1786, f8d), by Johannes Mart. Graberg,
one of Linnaeus' pupils, appears the follow^ing:

"That in the vegetable kingdom it is admitted that hybrid generations
exist, although rarely, see, from the 'Amoenitates Acad.' (t. 3, p. 28) of
our President, his solution of the St. Petersburg question concerning
the sex of plants, Petrop. 1760. A most satisfactory example of this fact
we have seen this summer in the Academic Garden ; here for several
years in the same bed grew Verbascum thapsus, and Verbascum lych'
nitis.'"

The origin of the presumed hybrid between these two species
appears to have been spontaneous, since the plant in question
seems to have come from naturally fertilized seeds of V. Lychnitis^
and was identified by Linnaeus with the specimen which Agerius,
one hundred or more years previously, had sentto Joh. Bauhin, who
gave the plant the name of "Verbassum angustifolium ramosum^
flore aureo^ folio crassiori^'' in his "Historia" (p. 856). Linnaeus'
plant is described as being similar to the female parent in the
branched stem, the filaments of the flowers, and in the other parts
of the inflorescence, but resembling the pollen parent in size, in
the calices, and in the somewhat decurrent leaves, which were yet
not so much so as in the male parent. Graberg concludes that :

24 PLANT HYBRIDIZATION BEFORE MENDEL

"All the observations concerning the generation of hybrid plants,
which we have hitherto instituted, show manifestly the interior plant or
fructification, to be similar to the mother, the exterior plant, however, or
'mask,' to repeat the image of the father." (8d, p. 293.)

Again it is stated :

"It is indeed true that numerous hybrid plants do not propagate the
species through the seeds, but it nevertheless does not follow that all
hybrids are sterile. For that new Tragopogon which our President pro-
duced and described in the St. Petersburg discussion, is propagated an-
nually from the seeds." {ib., pp. 293-4.)

The general conclusion regarding hybrids follows :

"in a word, when the stigmas of any plant are sprinkled with foreign
pollen, in some cases nothing occurs ; where such fecundation succeeds,
there proceed from these seeds when sown, plants called hybrids,
which, in the fructification, re-image the mother ; in the plant, however,
most strongly the father. These hybrids, thus born, are either fertile,
as Delphinium aconiti, Tragopogon hybridum, etc., or persist simply
sterile like mules, and if they flower they nevertheless produce no seeds,
as Verbascum Thapsus, Veronica Verbenae, etc. The flowers of these
sterile plants being examined, the anthers are observed to be sterile,
destitute of any pollen." {ib., p. 294.)

An interesting experiment of Linnaeus upon the banana is then
recounted as follows:

"Musa Paradisiaca, from its spadix, produces first female flowers ;
then at length the males ; the fruits of this Musa, before they flower,
have almost attained their proper size, and thereafter they are ma-
tured without any seed contained within the fruit. Hence it was said
that Musa is the only plant known, which is destitute of seeds, and is
multiplied by human means by dividing the roots. Accordingly, the
President hoped at some time to obtain two Musa plants flowering at
about the same time, so that he might fecundate the precocious female
flowers of the one with the pollen of the male flowers of the other,
which he did three years ago. When indeed he removed the anthers from
the male flowers for pollinating the pistils of the other, he observed all
these anthers in the male flowers to be altogether destitute of pollen.
Hence he concluded Musa Paradisiaca to be purely a hybrid plant,
sprung perchance from Musa Bihai as the mother, and from an undeter-
minable Indian father." {ib., p. 294.)

On November 23, 1751, appeared a discussion, included in the
"Amoenitates Academicae" (vol. 3, pp. 28-52, 1764) by another
of Linnaeus' pupils, Johannes Haartman, entitled "Plantae Hy-
bridae." (8b.)

This discussion upon hybrid plants is to be noted, insofar as
it reflects the views of Linnaeus and his school on the subject.

PLANTtE
HY B R I D iE,

Qaas
Sub PRiESIDIO

D:n. Doct* Caroli Linntei^

$:.E M.\£ M'TIS ARCHrjTRI, .

PUBLICJB DISQUISITION!

Siftit
Stipenditrius Neilelianus,
JOHANNES p.His HAARTMAN,
Aaftro-Fmlandus.

Vffalia 175-1. NovemB, z?.

Omnium fere tinsnimis diu fuit confenfus,
viva omnia ex iemiiie propagari ; fcetus e-
andem mtre viveiidi rationem, quam antea
parentes j. fingula intra fuas fpecies multiplicari,
atque adeo univerfa viventin , qualia in principio
inltirota erant, talia edam 111 pofterum fine fpecie-
rum, vet muiationc, vcl mixtione permanere. Ne-
que vero raeum eft propolltum hac occafionc, re-
ceptas illas ab eruduis opiniones refellere; muko
minus eximiis Creataris opcribus quid derrahere,
fed tantommodo ^tiones^ q\i«e tunjarum in regm
Vigeidiiii fpicieri&M §rmm ^r^are "ridentur, in me*

drum

Plate XVII. Title-page of the "Plantae Hybridae" of Johannes Haartnnan, 1751.

26 PLANT HYBRIDIZATION BEFORE MENDEL

The dissertation (Latin) opens with a somewhat brief philo-
sophical discussion of hybrids, particularly from the viewpoint
of whether or not "new species" could arise from genera. Cases
are given of 17 bigeneric crosses, 17 congeneric, 6 where con-
generic crosses gave rise to aberrations, such as crisping of the
leaves, etc., and 7 in the case of genera where the parentage is
uncertain.

Veronica maritima 9 X Verbena officinalis ^ is described in
the greatest detail fp. 35), and is illustrated. (8b, pi. 11.) This
natural hybrid is reported as having been produced in the Bo-
tanical Garden at Upsala in 1750. The statement is made "neque
longe ab his lecta est haec nostra planta ^ , quae antea nulli Bo-
tanico visa est." (p. 3^.) The vegetative and flower characters
are described in some detail. The hybrid was perennial, bloomed
annually, and was multiplied easily by the roots, but had no
fruit ("nullos vero fructus maturat"). (p. 35.)

This particular hybrid appears to have been derived from a but
slightly related parentage, viz., from the families Scrophulariaceae
and \'erbenaceae, respectively, belonging to the different sub-
groups Solaninae and Verbeninae of the Tubiflorae. Since its oc-
currence was made a subject for description, and since the date
of its appearance, and the observation of its characters (17^0)
precedes by ten years the hybrid Nicotiana paniculata ? X A^«
rustica ^ produced by Kol renter in 1760, it is of interest to pub-
lish the historical account, although as a matter of scientific fact
the Kolreuter hybrid marks the actual beginning of the genetics
investigation series.

The description of the plant is as follows :

In height, hoary color of the stem and leaves, smoothness of
the stem, structure of the spike, and color of the corolla, the plant
is stated to resemble the Veronica $ parent. If the flowers and
their color and the roundness of the stem were omitted, "the
most acute botanist would have considered it to be Verbena
itself" (p. 35) ; the leaves of the hybrid are said to have had
"exactly the same singular division, with deeply furrowed lobes"
(p. 35). The flowers are stated to have been smaller than those
of the female parent, and not larger than the flowers of Verbena',
the leaves "sometimes in threes, as in the 9 but more often oppo-

^LIa,

^y)ifei«s^T|gi!ia^»A'!«.-- '■'4iMiJ««*'«Wa»IW!MIII»

\l^<3^^ f^

Plate XVIII. Linnaeus' hybrid, Veronica maritima x Verbena officinalis.

28 PLANT HYBRIDIZATION BEFORE MENDEL

site as the S ." Although the plant flowered annually, it was
sterile, and bore no fruit, but was perennial and multiplied by
the roots.

"Floruit quidem haec planta omni anno felicissime, in annum quo haec
edimus, 1755,'et vivis radicibus facillime immutata multiplicatur, nullos
vero fructus maturavit." (p. 35.)

It thus appears that Linnaeus' hybrid Veronica, originating in
1750, was still alive in 1755.

Another hybrid, between Verbena hastata 9 and Verbena spuria
^ is stated to have originated naturally in the Botanical Garden
in 1748, perishing two years later. It is recorded as arising in the
same bed with the two species named above,

"but not through dissemination, considering that no one had the seeds
here hitherto, nor through a planting of it, since it had not previously
been seen within the country." (p. 43.)

The first description of the hybrid between Trifolium repens
9 and T. pratense $ , the now so well-known and widely-grown
"alsike clover" (T. hybridum) is given by Haartman (p. 44).
This hybrid is stated to have originated not only near Upsala,
but also near Aboa, "where I gathered it the past summer"
(1751). The description states:

"The white flower likewise commonly displays a purplish color, in
which it approximates to the father by as much as it recedes from the
mother. Besides, it bears the fructification of Trifolium album $ with all
its properties."

The account concludes :

"Paucis locis obvia est haec planta, nee veteribus nota, quod videtur
esse signum illam baud ita pridem generam fuisse." (p. 44.)

Perhaps the first exact description, aside from Kolreuter, of
intermediate characters in a hybrid, is also given by Haartman
(p. 48), in the description of a hybrid Thalictrum referred to as
a "new plant recently seen in the academic garden." The num-
ber of the stamens is given as 40, and of the pistils, 8 ; those of the
female parent being 60 and 16, and of the male parent, 16 and 7,
stamens and pistils, respectively ; the hybrid was therefore inter-
mediate.

A hybrid, Helianthus multiflorus, between Helianthus annuus
9 and H. tuberosus 5, is described as having fibrous roots like
the 9 parent.

PLANT HYBRIDIZATION BEFORE MENDEL 29

In all, Haartman gives a list of 100 hybrid plants, of which
descriptions are given in the case of 59. The cases most note-
worthy from the historical standpoint have been cited.

On June 11, 1746, appeared, as Dissertation 9, in the "Funda-
menta Botanica," the "Sponsalia Plantarum" (8a) of Johan.
Gustav Wahlbom, one of Linnaeus' pupils, which undoubtedly
also represents the ideas of Linnaeus himself. Since this essay con-
sists entirely of a general discussion upon the sex of plants, it will
not be necessary to take it into consideration here.

BIBLIOGRAPHY

1. Aristotle.

(a) Aristoteles Graece ex recensione Immanuelis Bekkeri,
edidit Academia Regia Borussica. Berolini apud Geor-
gium Reimerum, ex officina Academica. 4 vols. 4to, Ber-
lin, 1831.

(b) The works of Aristotle translated into English, under
the editorship of J. A. Smith, M.A., and W. D. Ross,
M.A., Oxford, at the Clarendon Press, 1912. Vol. 5, De
Partibus Animalium, by William Ogle ; De Motu and
De Incessu Animalium, by A. S. L. Farquharson ; De
Generatione Animalium, by Arthur Piatt. Vol. 6, Opus-
cula ; De plantis, by E. S. Forster, pp. 815-29. (For the
case of the date palm, see p. 820; Bk. 1, 6.)

2. Camerarius, Rudolph Jakob.

(a) Academiae Caesareo-Leopold. N. C. Hectoris 11. Ru-
dolphi Jacobi Camerarii, Professoris Tubingensis, ad
Thessalum, D. Mich. Bernardum Valentini, Professorem
Giessensem, De sexu plantarum epistola, Tubingen
1694. Vol. 8, no pp.

(b) De Sexu Plantarum Epistola (extracts).

(1) Appendix ad annum tertium ephemeridum medico-
physicarum academiae Caesareo-Leopoldinae Na-
turae Curiosorum in Germania. Norimbergae, Anno
1696. (pp. 31-6.)

30 PLANT HYBRIDIZATION BEFORE MENDEL

(2) The response, "Responsoria," of Valentin, follows
(pp. 32-40), under the title, "Dn. Michaelis Bern-
hardi Valentini Responsoria ad Dn. D. Rudolphi
Jacobi Camerarii Epistolam de sexu plantarum."
The complete title of the Camerarius publication
above reads : "Dn. D. Rudolphi Jacobi Camerarii
Med. D. & P. P. xAcad. Caesareo-Leopold. N. C.
Colleg. d. Hect. 1 1 ad Dn. D. Michaelem Bernar-
dum Valentini, Prof. Giessensem & Curios. Thes-
salum de Sexu Plantarum Epistola."
The title-page of the volume of the "Ephemerides,"
above cited, is as follows : "Miscellanea Curiosa
sive Ephemeridum Medico-Physicarum Germani-
carum Caesareo-Leopoldinae Naturae Curiosorum.
8 MDCXVI Decuriae 111. Annus Tertius, An-
norum MDCXCV Continens. Celeberrimorum Viro-
rum tum Medicorum, tum aliorum Eruditorum in
Germania, & extra eam, observationes Medico-
Physico-Anatomico-Botanicas. Cum Appendice, ec
Privilegio Sac. Caes. Majestatis. Editio sumtibus
Academiae 1696 Lipsiae apud Thomam Fritschium
et Francofurti apud Joh. Philippum Andream. Lit-
eris Knorzianis.

(c) tJber das Geschlecht der Pflanzen (De Sexu Plantarum
Epistola, 1694) von R. J. Camerarius. tjbersetzt und
herausgegeben von M. Mobius. Leipzig 1899. 50 pp.
No. 105 of Ostwald's "Klassiker der exakten Wissen-
schaften."

3. Fairchild^ David G.

Persian Gulf dates and their introduction into ^America. Bu-
reau of Plant Industry, U. S. Department of Agriculture,
Bull. 54, December 19, 1893.

4. Hehn^ Victor.

Kulturpflanzen und Haustiere, in ihren Ubergange aus Asien
nach Griechenland und Italien sowie in das iibrige Europa.
8th ed. by Prof. Dr. O. Schrader, Berlin, 1911.

PLANT HYBRIDIZATION BEFORE MENDEL 31

5. Herodotus of Helicarnassus. circa 484-425 B.C.

(a) Herodoti musae suae historiarum libri LV, ad veterum
codicum fidem denuo recensuit lectionis varietate con-
tinua interpretatione latina adnotationibus Wesselingii
et Valckenorii aliorumque et suis illustravit Johannes
Schweighauser. Argentorati et Parisiis apud Treuttell et
Wortz Bibliopolas MDCCCXVI, 6 vols. Text, Greek
and Latin, and Index rerum et personarum, Vols. 1-4;
Adnotationes, Vols. 5, 6. (On the pollination of the date,
1 : 234. Bk. 1, Cap. 1913.)

(b) Herodotus, Historiae, with an English translation by
A. D. Godley, 4 vols. London, 1921. (On the pollina-
tion of the date; text, 1:244; trans. 1:245.)

6. Kazwini.

Zukariyya ibn Muhammed ibn Mahmud al-Qazwini ; Text
with French trans, in de Sacy, Chrestomathie Arabe, 1st ed.,
3 vols., 8 vo., Paris 1806; 2nd ed., 3 vols., 8 vo., Paris 1827.
(For pollination of the date palm, see 1st ed., 3:369-413,
2nd ed., 3:387-426.)

7. Kearjiey^ Thomas H.

(a) The date gardens of the Jerid. Nat'l Geog. Mag. 21 :543.
July 1910.

(b) The country of the ant-men. Nat'l Geog. Mag. 22 :267.
April 1911.

8. Linne, Carl von, and Pupils.

(a) 1746 (June 11). Sponsalia Plantarum, by Johan. Gus-
tav Wahlbom. Amoenitates Academicae ; 1:61-109.
(Haak, 1749.)

(b) 1751 (November 23). Plantae Hybridae, by Johannes
Haartman. Amoenitates Academicae; 3:28-62. (Hol-
miae, 1764).

(c) 1760 (September 6). Disquisitio de sexu plantarum, ab
Academia Imperiali Scientiarum Petropolitana praemio
ornata, by Carl v. Linne. Amoenitates Academicae, 10,
100-131. (Erlangae, 1790.)

PLANT HYBRIDIZATION BEFORE MENDEL

(d) 1762 (October 16). Fundamentum fructificationis, by
Johannes Mart. Grdberg. Fundamenta Botanica, Diss.
No. 8, CXVI; 1:169-214, 1786. Also Amoenitates Aca-
demicae, Diss. CXVI; 6:279-304. Holmiae, 1763.

The publication of the ten volumes of the "Amoenitates" is as
follows :

Vol.

— »

5'
6,

10,

Lugduni Batavorum (Leiden), Haak,
Holmiae (Holm), Salvius,

((

Erlangae (Erlangen), Schreber,

1749
1762

1764

1759

1760

1763
1769
1785
1785
1790

The first nine volumes contain altogether 186 dissertations.
Vol. 10 contains ten addresses, followed by four scientific con-
tributions, "Dissertationes Botanicae."

9. Mason^ S. C.

Dates of Egypt and the Sudan, Bureau of Plant Industry,
U. S. Dep't of Agriculture, Bull. 71, Sept. 1925.

10. Marceilinus, Ammianus.

Ammiani Marcellini rerum gestarum libri qui supersunt. ed.
Carolus U. Clark, adjuvantibus Ludovico Traube et Guli-
elmo Heraeo. Berlin, 1810, Vol. 1, Libri XIV-XXV. (Concern-
ing the date palm, see Bk. 24, 3, 12-13.)

11. Pliny (Gains Plimus Secundus).

(a) G. Plinii Secundi Naturalis Historiae Libri XXXVIII. Re-
censuit lulius Sillig. 8 vols., Hamburg & Gotha, i8';i.
(Concerning the date palm, see Bk. 13, ill, 7.)

(b) The Natural History of Pliny, translated by John Bos-
tock and H. T. Riley, 6 vols., Henry G. Bohn, 1855.
(See 3:171-2.)

PLANT HYBRIDIZATION BEFORE MENDEL 33

12. Popenoe^ Paul B.

(a) Babylonian dates for California. Pomona College Jour,
of Economic Botany, 3:459, May 1913.

(b) The pollination of the date palm. Journal of the Amer-
ican Oriental Society, 41 :343-54, 1922.

13. Strabo.

(a) Strabonis geographica, curantibus C. Mullero et F. Du-
buero, I Vol. Paris, 1853. (See Bk. 17, Cap. 1.)

(b) The geography of Strabo, with an English translation
by Horace Leonard Jones, 8 vols., i6mo. London and
New York, 1917.

14. Swingle, Walter T.

The date palm and its utilization in the southwestern states.
Bureau of Plant Industry, U. S. Dep't of Agriculture, Circ.
19. June 1913.

15. Theophrastus.

(a) Theophrasti Eresii quae supersunt opera et excerpta li-
brorum, ed. G. Schneider, 5 vols. Leipzig, 1818. (Vol. 1,
Greek Text: Vol. 2, Latin trans. De historia plantarum,
200 pp.; De causis plantarum, 194 pp. (See on the date
palm, De Hist. PL, Bk. 2 ; Cap. 6 & 8.; De Causis PL,
Bk. 1, Cap. 20; Bk. 2, Cap. 9, Bk. 3, Cap. 18.)

(b) Inquiry into plants, and minor works on odors and
weather signs, with an English translation by Sir Arthur
Hort. 2 vols. i6mo. London and New York. 1916.

CHAPTER II

8. Kdlr enter (1733-1806).

CAMERARIUS' memoir fell on sterile, or rather on unpre-
pared soil. Over half a century elapsed before one was
found to speak his praise as follows:

"Rudolph Jacob Camerarius is indisputably the first who proved the
sex of plants through his own experiments instituted from this point of
view. He, my fellow countryman, it is whom the learned world has
principally to thank for this great truth, which is so general, and of
such great influence upon the physical and economic sciences. Camer-
arius it was, who criticised in the most fundamental way everything of
this material, as well that which was found in the oldest as in the new-
est writings of his time ; compared them with one another and, to-
gether with a quantity of his own observations and useful applications,
whereby the theory of this truth has now been strengthened, laid the
matter before the learned world in a letter to Mich. Bernard Valentin."

These were the words of Joseph Gottlieb Kolreuter. From the
25th of August, 1694, th^ <^^te of Camerarius' letter concerning
his experiments upon sex in plants, until September 1, 1761,
there was made no fundamental progress in the real scientific
knowledge of the phenomena of inheritance. On this latter date
appeared Kolreuter's "Preliminary Report of some Experiments
and Observations concerning Sex in Plants." This report was fol-
lowed in 1763, 1764, and 1766, by three supplementary papers on
the same subject, which record the results of 136 distinct experi-
ments in the crossing of plants.

If Camerarius made the actual scientific discovery concerning
sex in plants, Kolreuter was the first to give to this discovery
scientific application. He was born x\pril 27, 1733, in the Swabian
village of Sulz, in the valley of the Neckar, in the Black Forest
region of Southwest Germany. From 1760 to 1764, he conducted
his experiments, partly in his native village, partly in the garden
of a physician, Achatius Gartner, in the town of Calw in Wiir-
temberg, and partly in St. Petersburg, Berlin, and Leipzig. From
1764 until his death in 1806, he was Professor of Natural His-

fLMl. AiA. J. l,j. I\l)l I ClUir I , 1/33-1806.

36 PLANT HYBRIDIZATION BEFORE MENDEL

tory in the University of Karlsruhe. At Sulz, in 1760, Kolreuter
produced the first plant hybrid obtained in a scientific experiment.
Kolreuter's most important papers, his "Vorlaufige Nachricht,"
and its three 'Tortsetzungen" (1), cover a reported period from
1760 to 1766. In the former year, Kolreuter secured his first hy-
brid, Nicotiana paniculata 9 y<( N. rustica 5 . The experiments
during the following six years, numbering 65 definitely described,
covered crosses involving 13 genera and 54 species. Before tak-
ing up these experiments in detail, and especially those of ge-
netic interest, it will be well to deal with Kolreuter's views or
conclusions with respect to the fertilization process and hybridiza-
tion. In the first place, it will be understood that Kolreuter worked
with the microscope. Sprengel indeed remarks, regarding the for-
mer's study of pollination in Asclepias, that some of the observa-
tions therein he himself had not been able to make. "Da ich kein
so gutes Vergrosserungsglas zur Hand gehabt habe, als Kolreu-
ter." (2, 1 : 165.) It is desirable also to remember that Kolreuter
not only carried on his investigations upon hybrids, but made
extensive observations upon pollination. Indeed it is possible
that Sprengel's title for his work "Das entdeckte Geheimniss
der Natur," (1793) may have been suggested by Kolreuter's
remark, "Gewiss ein jeder anderer, der vor mir diese Betracht-
ungen angestellet hatte, wiirde sie langst entdeckt, und sich
und alien Naturforschern von diesem Geheimnisse der Natur den
Vorhang langst weggezogen haben." (p. 21.) Kolreuter himself
alludes to his use of a "Vergrosserungsglas," in his search for the
stigmatic surfaces in Iris (i, p. 22), and in the examination of
the pollen in his first Nicotiana hybrid, (p. 31.)

Kolreuter considers that the pollen is a collection of organic
particles, which have a definite form in every plant. In structure,
the pollen grain consists of an outer thick membrane or rather
of a hard and elastic shell, upon which, at equal distances apart,
are found the "excretion-canals" and openings for escape of the
male fertilizing material. In the species in which the pollen grains
are beset with projections, these excretion-canals are in the pro-
jections themselves, being found at their apices. Within the elas-
tic shell, there is stated to be a netlike mass of vascular fibres
which, in some species, is arranged in almost regular hexagonal
fashion; in others, in some other more or less regular way.

PLANT HYBRIDIZATION BEFORE MENDEL 37

"Through the substance of this elastic shell," says Kolreuter, "one
sees an extended net of vascular fibres which, in a few species of pol-
lens, is divided off into almost regular six-sided eyes, in others in an-
other more or less regular way." (p. 7.)

Each such division or "eye" serves as the point of location for
one of the elevations or projections, in which an excretion-canal
terminates. Immediately beneath the outer shell is a thinner,
weaker, white membrane, beneath which is

"an apparently cellular tissue, which fills the entire cavity of the pol-
len grain and is, as it were, the nucleus (Kern) of the latter." (p. 8.)

It is probable that the Kolreuter idea would be better translated
by the word "kernel" than by the word "nucleus," with its mod-
ern connotations. This material or substance which, in the unripe
condition, is described as granular, firm and half-transparent,
finally at maturity passes over into a uniform, fluid, and trans-
parent material, which comes out of the "cellular tissue." The
words "cellular tissue" (zellenformiges Gewebe) must likewise
not be taken in the sense of "tissue-cells," but in the sense of a
body or mass of something, enclosed in a cell-like envelope.
Nothing more definite than this could possibly have been seen by
Kolreuter. The tube and generative cells, the only "structures,"
visible within the pollen grain through the walls of the exine,
that could possibly be taken in any sense as "cellular," may have
been visible to Kolreuter's microscope. In this "tissue," at all
events, is said to be found the entire mass of the male fertilizing
material.

The divisions or "eyes," thought by Kolreuter to be within the
"elastic shell," are evidently the more or less geometrical reticula-
tions on the outer surface of the exine of the pollen grain in many
species. The escape of the contents of the pollen grains is consid-
ered to be brought about by the contraction and pressure of its
thick outer coat. In consequence of this pressure, the contents are
expelled through the "excretion canals" on all sides at once. The
swelling of the pollen grain is presumed to take place through
the absorption of water. With the beginning of maturity of the
contents of the pollen grain, the inner coat acquires firmness and
elasticity and, by virtue of this, presses from all sides upon the
fertilizing material within, which has now become fluid, and forces
it into the place of least resistance, the open excretion canals.

38 PLANT HYBRIDIZATION BEFORE MENDEL

(p. 8.) This is the character of the pollen grain and the manner
of its germination as Kolreuter conceived it.

The male fertilizing material, as well as the secretion upon the
stigmas, is considered to be of an oily nature. These two secre-
tions commingle with one another, when they come together, in
the most intimate manner and make, after commingling, a uni-
form mass, which, when fertilization ensues, is sucked in by the
stigma, and must be conducted through the style to the ovules, —
the so-called "seed-eggs" (Saameneyern) or unfertilized "germs"
(Keimen). Kolreuter recognizes that a certain number of pollen
grains are required for fertilization in every flower, but this
number, in comparison with the number produced, is very small.
Kolreuter remarks that, in a Ketmia flower of average size, 4,863
pollen grains are produced, but that, for the fertilization of the
30-odd seeds in a single capsule, not more than 50-60 pollen
grains are required. He found that, the more the number of pol-
len grains fell below this number, proportionately fewer were the
number of seeds produced. If as few as 15 or 20 pollen grains
were used, only 10-16 seeds were fertilized, (p. 12.) It was found,
moreover, that with this small number of pollen grains the seed
capsule after a time began to wilt, and finally fell off. If fewer
than 10 pollen grains were used, "then it was just as though 1
had taken none at all." No trace of fertilization followed, and
the ovary degenerated and fell off, in still less time. This ex-
periment tallies closely with the preceding one, in demonstrating
that, in the species in question, about two pollen grains are re-
quired on the average per ovule, making allowances for the
failure of some grains to germinate, and for the failure of the
pollen tubes of others to reach the ovary. These latter details
were entirely unknown to Kolreuter, who believed he was dealing
with a mass effect. In the common Mirabilis jalapa the number
of pollen grains reached 293, and in a Peruvian species, 121 ; but
of this number but one, or at most two or three, were required
for fertilization. Kolreuter found by experiment that in a plant
with 2-5 stigmas, by abscission of all but one, and pollinating
that one "with a sufficient quantity of pollen" (p. 13), ripe seeds
developed in all the cells of the ovary. He states this was found
even to be the case in plants in which the stigmas were separated
to the base, as in Paris. This was so also in Hypericum he says,

PLANT HYBRIDIZATION BEFORE MENDEL 39

in which each of the five separate stigmas is directed outward
toward its own cell of the ovary. Kolreuter made rather extensive
examinations of the pollen grains of several hundred genera, and
comments on their form and relative sizes. He remarks on the
fact that, in almost all grasses, the stigmas are self-pollinated
within the closed flower. He comments at some considerable
length upon the manner of pollination of a number of species,
and especially upon the fact of pollination by insects. Regard-
ing the activity of insects in fertilization, the only example thus
far known, he says, is the fig tree :

"is it then," he continues (p. 19), "something so wholly exceptional, if
Nature, for the maintenance of certain creatures, makes use of others
which have no resemblance with them. Experience has taught me pre-
cisely the truth of this, that has long been maintained for the fig tree,
and for the case of many other and in part very common plants. In all
the Cucurbitaceae, in all the Iridaceae, and with not a few plants from
the order of Mallows (Malvaceae), fertilization of the female flowers
and stigmas occurs only through insects."

In speaking of the fact that cucumbers and melons, confined
within hot-beds, do not set fruit, he says :

"Up to the present day one has ascribed to the wind the pollination of
the female flowers ; but one would necessarily have had to come to
other ideas, if one had only brought the location of the male and fe-
male flowers, their form, and the structure of the pollen into closer
observation." (p. 20.)

He then continues :

"And how can one do this, without immediately finding the cause of
the pollination in those busy creatures (i.e., the insects). Certainly, any
other one, who before me had instituted these observations, would have
long since discerned them, and have drawn aside the curtain of this se-
cret of Nature for himself and all investigators of Nature." (p. 20.)

Kolreuter investigated the pollination of the Iris (pp. 22-4),
and describes with scientific and minute exactness the details of
his discoveries. He was apparently the first to discern the actual
location of the stigmatic surfaces, in the triangular area toward
the apices of the leaf-like so-called stigmas, the inner surfaces of
which he found to be covered "over and over with pointed papil-
lae" smeared with a moist secretion.

"I did not let the matter rest there," he says, "but instituted very many
experiments thereupon, which finally completely convinced me that this
small part is the true stigma in these plants." (p. 23.)

The opening of the flower, and the relations of the several

40 PLANT HYBRIDIZATION BEFORE MENDEL

parts, are described at some length, and the pollination discov-
ered to be by means of humble-bees.

From his experiments with the Iridaceae and Malvaceae, Kol-
reuter concludes :

"l have instituted very many and various experiments and observa-
tions, w^hich have completely convinced me that the pollination of the
stigmas (in the two groups mentioned) is not to be ascribed either to
the location which the parts of the flower have to one another, nor to
the wind, but simply to the insects alone." (p. 25.)

Kolreuter also comments on the fact that:

"if one takes away at the same time from a certain number of flowers
their still closed anthers, yet their stigmas will always be covered over
with a sufficient quantity of pollen, which the insects carry thither from
other flowers standing in the neighborhood." (p. 27.)

Thus concludes the general botanical discussion in Kolreuter's
first Nachricht, which occupies a space in the Oswald edition of
28 pages, and which has been discussed at length because it is
seldom commented upon, and because it shows the preliminary
preparation for his hybridization experiments which Kolreuter
obtained through natural history investigations at first hand.

The development of the pollen tube was not known in Kolreu-
ter's time, having been first observed by Amici in Portulaca in
1823; the penetration of each pollen tube into the ovary and to
the micropyle of the ovule, by the same investigator in 1830;
and the development of the embryo from an egg cell already
present in the embryo-sac before the arrival of the pollen-tube,
which stimulates it to further development, also by Amici in
1846. (Sachs, "Hist, of Bot.," 432.) The number of 50-60
pollen grains, found by Kolreuter by experiment to be the mini-
mum number requisite for the fertilization of the 30 or so seeds
in a capsule, represented to Kolreuter's mind in a manner the
mass amount of the "exudate" required. This latter was sup-
posed, as stated, to be excreted by compression from the matur-
ing pollen grain upon the stigma, there absorbed, and drawn
through special conduction or secretion canals into the interior of
the ovary.

One can, Kolreuter continues (p. 21), by exposing the female
flowers to the wind, while excluding the approach of insects, con-
vince himself, through the immediately succeeding death of the
ovary, that pollination in such plants could not occur by means

PLANT HYBRIDIZATION BEFORE MENDEL 41

of the wind. Kolreuter then describes, in very considerable detail,
the pollination process in Iris, in the mallows, and in the water-
lilies. In Argemone, Hypericum, Oenothera, Epilobium, Polemo-
nium, Echium, Hyoscyamus, Nicotiana, Antirrhinum, Scrophularia
and others, certain details of the pollination process are more
briefly remarked upon. The general discussion of pollination
concludes as follows :

"Everywhere, insects are always involved, in the case of plants in
which pollination does not ordinarily occur through direct contact ; and
they have the most to do with their pollination, and consequently also
with their fertilization, and probably they furnish, if not to all plants,
at least to a very great part of them, this uncommonly great service :
for almost all flowers belonging here carry something with them that is
agreeable to insects, and one will not easily find one of them with which
they are not to be found in quantity." (p. 28.)

Kolreuter now begins his discussion of hybrids. Many so-called
hybrids are probably products of the imagination. There are per-
haps scarcely any among them which might rightly deserve this
name.

"How can one give them out with certainty as such," he says, "before
one has produced them through art and, indeed, through the most un-
remitting experiments." (p. 29.)

The First ''Mule Plant."

In rather naive fashion Kolreuter describes the reasons which
led him to experiment upon the breeding of plants. He calls at-
tention to the fact that man has brought together, in botanical
and zoological gardens, plants and animals from all quarters of
the earth. With animals, this has given rise to the possibility of
making hybrids. The history of Kol renter's first hybridization ex-
periment is given as follows :

"As improbable as it is, that of two different kinds of animals, which
have lived in their natural freedom, a hybrid should ever have been
produced, so improbable is it also that, in the orderly arrangement that
nature has made in the plant kingdom, a hybrid plant should have
arisen. Nature, which always, even in the greatest apparent disorder,
adheres to the most beautiful order, has precluded this confusion, in the
case of wandering animals, aside from other means, through the natural
instincts, and in the case of plants, in which their all too close proximity,
the wind, and insects, give a daily opportunity for an unnatural inter-
mixture, she will without doubt have known, through just as certain
means, how to take away their force from the operations to be feared
therefrom. Presumably, aside from the natural instincts, they are just
the same as occur with animals. Perhaps it has also been one of her
designs to preclude such a disarrangement to be feared therefrom, that

A r« «.

42 PLANT HYBRIDIZATION BEFORE MENDEL

she has transferred one plant to Africa, and assigned to another its
place in America. Perhaps in part for this reason it has happened, that
she has enclosed within the boundaries of a certain region only such
plants as, in regard to structure, have the least resemblance amongst
themselves, and which, consequently, are also least qualified to cause a
confusion amongst themselves, if these conjectures have their founda-
tion, as I almost believe, then, in the botanical gardens, where plants of
all kinds and from all parts of the world, are together in a narrow
space, hybrid plants will probably be able to originate, especially if one
puts them together according to a systematic arrangement, and conse-
quently those which have the greatest resemblance to one another. Man
at least here gives to plants, in a certain manner, the opportunity which
he gives to his animals brought from parts of the world lying far dis-
tant from one another, Avhich he keeps confined, contrary to nature, in
a zoological garden, or in a still narrower space. Would indeed a gold-
finch ever have mated with a canary bird, and have produced hybrid
offspring, if man had not provided for them the opportunity of coming
to know one another more closely^ Should not, therefore, hybrid plants
have already arisen in botanical gardens '? Precisely the reasons, which
to me made their production under natural conditions suspicious, move
me to admit it under this unnatural one. Because I had already been
long convinced of the sex of plants, and had never doubted the possi-
bility of such an unnatural procreation, yet I still allowed mj^self to be
deterred by nothing from instituting experiments on this subject, in the
good hope that I might perhaps be indeed so fortunate as to procure a
hybrid plant. I have finally in fact, after many experiments instituted in
vain with many kinds of plants, in the past yea.T of 1760, in the case of
two different species of a natural genus (bey zwoen verschiedenen Gat-
tungen eines natiirlichen Geschlechts), namely, in the case of Nicotiana
{paniculata) [Linn. Sp. Pi., p. 180, n. 2], and Nicotiana (rustica) [Linn.
Sp. Pi., p. 180, n. 3], gotten so far that I have fertilized with the pollen-
dust (Saamenstaube) of the former, the ovary of the other, obtained
perfect seeds, and from these, still in the same year, have raised young
plants." (la, pp. 29-30.)

Regarding the nature of his experiment, Kolreuter says:

"since I have made this experiment with many flowers, at different
times and with all possible precaution, and have thereby every time
obtained normal fertilization and perfect seeds, I could not in the least
believe that perchance an oversight might have occurred in the experi-
ment, and that the plants already produced from the seeds, of which
seventy-eight had come from a hundred and ten seeds, should be only
ordinary mother plants. Although I could not immediately quite dis-
cern much in them that was unusual and strange, yet I had already
found a noticeable difference between the natural seeds and those pro-
duced artificially, which let me doubt so much the less of the young
plants grown therefrom not being true hybrids. I was finally completely
convinced of it, when more than twenty of them which I had kept over
winter, partly in the room and partly in a cold green-house, came into
flower in the month of March just past. I was with much satisfaction
aware, that not alone in the spread of the branches, in the position and
color of the flowers throughout, they held precisely the mean between

PLANT HYBRIDIZATION BEFORE MENDEL 43

the two natural species, but that with them especially also all the parts
belonging to the flower, the anthers alone excepted, taken in comparison
with those of the two natural plants, showed an almost geometrical pro-
portion." {ib., pp. 30-1.)

The anthers of the hybrid Nicotiana contained less pollen than
those of the parents, and instead of having their regular elliptical
form

"they were in comparison quite irregular, shrivelled as though rubbed to
pieces ; they contained almost nothing of a fluid material, and were, in
a word, simply empty husks." {ib., p. 31.)

Kolreuter then goes on to say :

"The fertility of this new plant appeared to me, therefore, extremely
questionable, and the results confirmed my suspicion completely ; for
among the almost innumerable quantity of flowers there was not one
to be found which had borne even a single seed, even though they had
been immediately covered with a large quantity of their own pollen
dust ; while on the other hand, with the two natural species, every
capsule is accustomed to bear four or five hundred seeds. This plant
is thus in the real sense a true, and, so far as it is known to me, the
first botanical mule which has been produced by art." {ib., p. 31.)

In this connection Kolreuter refers as follows to the supposed
hybrid Tragopogon^ reported by Linnaeus to the Imperial Acad-
emy of Sciences at St. Petersburg, and which bloomed in the bo-
tanical garden at St. Petersburg in the spring of 1761, as being
in his expression "only half a hybrid."

"For the hybrid goat's-beard, which the celebrated Linnaeus considers
in his new prize essay, is not a hybrid plant in the real sense, but at
most only a half hybrid, and indeed in different degrees, as I will clearly
and plainly demonstrate at another opportunity, with many reasons
which appear in part from the nature and peculiarity of the composite
flowers, and from certain experiments instituted upon the time of fer-
tilization of the same ; in part from the structure of the above-mentioned
presumed hybrid itself, which had been raised by me from seeds which
Linnaeus had sent, together with his prize essay, to the Honorable Rus-
sian Imperial Academe' of Sciences, and which have bloomed the past
spring in the Academy's garden at St. Petersburg." {ib., p. 32.)

The hybrid Nicotiana paniculata -.X rustica obtained by Kdl-
reuter, he pollinated, in part with the pollen of paniculata and in
part with that of rustica^ and obtained fertile seeds in both cases,
but in lesser numbers than with the self-fertilized parents. Kol-
reuter's conceptions regarding hybrid fertilization, and the pro-
duction of what he refers to as a half hybrid appear in the next
following pages. His conception is that from any plant, from

44 PLANT HYBRIDIZATION BEFORE MENDEL

which, through fertilization with another, a complete hybrid
can be produced, a mere "tincture," as it were, may likewise be
transmitted, in the proportion in which its own pollen stands to
that of the other that is also purporting to function as the male
parent in the fertilization process. This "tincture," or supposed
partial contribution of the female parent, through the agency of
its own pollen, is presumed by Kolreuter to be (p. 34) the cause
of the production of "half-hybrids." This conception of the effect
of the pollen as a mass-effect, brought about through the secretion
of fertilizing substance by the pollen grains, which was the
more effective the greater the quantity of it, was the prevailing
theory for some time after Kolreuter's day. Kolreuter's first
"Vorlaufige Nachricht" closes with a brief discussion of six ex-
periments which he conducted with regard to nectar-producing
plants (pp. 34-7), and which need not be referred to here.

The first "Fortsetzung" to the preceding appeared in 1763.
The "Vorlaufige Nachricht" was dated September 1, 1761, the
place of publication not appearing. The first "Fortsetzung" is
dated at Calw, December 10, 1762. At this time Kolreuter
appears in the publication as Professor of Natural History at
Wiirtemberg. The preface opens with Kolreuter's expression of
conviction, that from the experiments in the preceding report the
sex of plants was most completely proved, as well as the theory
that reproduction in plants resulted from the production of two
kinds of fertilizing material. The "Fortsetzung" therefore begins
with the statement :

"To the production of every natural plant two similar fluid materials
of different sort are demanded. The one of these is the male, the other
the female."

Since these materials are of different sort, or are different from
each other in their nature, it is therefore easy to understand that
the force or strength of the one must be different from that of
the other.

"From the union and commingling of these two materials, which oc-
curs most intimately and in an orderly manner according to a definite
relationship, there arises another of an intermediate sort, and which
consequently also possesses an intermediate composite force, arisen from
those two simple forces, just as through the union of an acid and an
alkaline substance a third or intermediate salt originates." (p. 42.)

It is worthy of mention that Kolreuter records, regarding his

PLANT HYBRIDIZATION BEFORE MENDEL 45

first Nicotiana hybrid, its much more rapid growth, whereby it
was distinguishable from its two parents, as he says, "from the
germinating seed on to its complete flowering." (p. 32.)

Kolreuter seems to have interpreted the phenomenon of the
hybrid in a completely teleological way. The hybrid plant pro-
ceeds in its development normally like any other plant.

"Even in the case of the most completely infertile hybrid the keenest
eye can discern no incompleteness, from the embryo up to flower forma-
tion, and yet the most important character, fertility, is lacking, a circum-
stance that would not be suspected from observation. But instead of an
expected number of some 50,000 seeds, none are obtained, and more than
a thousand flowers, one after another, are seen to fall, without leaving
a single capsule behind." (ib., pp. 43-4.)

"Certainly," he says, "this event is, for a scientific investigator, one
of the most deserving of astonishment that has ever occurred upon the
wide field of nature." {ib., p. 44.)

The wonderful and unexpected thing, however, to Kolreuter's
mind, lay not in the union of two materials,

"which indeed were not destined for each other by the wise Creator,"
but rather in the fact "that precisely this plant, when it has reached the
highest pitch of its completion, is not in condition to fulfill the final
object toward which otherwise all the operations demanded for de-
velopment appear to be directed, and, in all its apparent completeness,
betrays the greatest incompletion that a plant can ever happen upon.
This incompleteness consists chiefly in the total lack of good male and
female fertilizing material (Saamen), and in the infertility naturally
arising therefrom." {ib., p. 44.)

Kolreuter's mind, however, reaches out into the conceived pre-
existing harmony of nature, which must be preserved at any
cost, and this apparent incompleteness becomes resolved into the
completeness of an orderly-minded creative agency which abhors
confusion of any kind, at least not of its own originating. He
proceeds further :

"if one regards this event, however, from the point of view of its
consequences, then one will recognize with pleasure that this actual in-
completeness is real completeness. What an astonishing confusion would
not the peculiar and unchanged hybrid characters, and the continually
retained fertility of such plants give rise to in Nature." (p. 44.) . . .
"what evil and unavoidable consequences must these not draw after
them*?" {ib., p. 44.)

Kolreuter turns from the contemplation of this embarrassing
picture, to raise what seemed to him a serious scientific question
that appeared to be involved.

46 PLANT HYBRIDIZATION BEFORE MENDEL

"Experience teaches us," he says, "that from the union of two like-
formed fluid fertilizing materials of different sorts a firm and organic
body originates, and that every natural plant itself provides those two-
fertilizing materials required for a new procreation, and especially the
one of them, namely, the male, apparently in much larger measure than
was necessary for its reproduction." {ib., p. 44.)

On the other hand, according to Kolreuter's view, an artificial
process seems to be quite impotent for fertilization purposes, or
else it brings it about only in a very limited and incomplete way.
This circumstance he holds to be one of the most complicated
knots in the whole doctrine of reproduction,

"to the solution of which all human understanding taken together might
still perhaps be too weak." He concludes that: "I will hence not in the
least break my head on it, but simply lay it down as a fundamental ex-
perience when, later on, the question arises of the explanation of various
remarkable characters of a few of the plants obtained from my experi-
ments." (p. 45.)

Thus concludes the theoretical or introductory portion of the
"Fortsetzung." Of the experiments which follow, 18 are with
species of Nicotiana^ one with Dianthus, one with Ketmia^ one with
Leucojum^ and one with Hyoscyamus.

Of the Nicotiana crosses, five are too complicated to be of
genetic value, consisting either of crosses of one F^ hybrid with
a different one, or of an F^^ with a cross between a species and
another F-^. Nine of the crosses might be considered interesting
from the genetic standpoint, being either crosses between species,
selfing of F^'s or back crosses on an F^^ by one of the parents and
vice versa.

Kolreuter made, besides other crosses between species of Nico-
tiana^ crosses between species of Ketmia^ pink {Dianthus)^ stocks
(Matthiola), dogbane (Hyoscyamus) , and mullein (Verbascum).
He ascertained the fact that, in general, only nearly related
plants, and not always even these, can be crossed. He determined
experimentally the fact that, if the stigmas of flowers are polli-
nated at the same time by their own pollen and by pollen from
another species, fertilization is effected by the former, which
would account for the comparative rarity of "species hybrids" in
nature.

The cross Nicotiana rustica X paniculata was repeated, 24
plants resulting, which resembled in behavior those of the first

PLANT HYBRIDIZATION BEFORE MENDEL 47

experiment. These, as well as the hybrids in the former case,
were found, after most careful experimentation, to be in a slight
degree fertile as to the egg-cells, but completely sterile as to the
pollen. Kolreuter comments regarding this cross that, in size of
the plants and number of flowers, the hybrids far exceed the
rustica parent. Whether they exceed the paniculata parent in
these respects, he was not prepared to state.

In case of Nicotiaria paniculata X rustica and its reciprocal,
the Fj hybrids resembled each other completely. In the case of
the back-cross of rustica upon lustica X paniculata^ all the prog-
eny are reported to have approached the type of the maternal
parent, i.e., the F^ hybrid ; a few more, others less. The cross,
A^. rustica X paniculata^ is reported as furnishing progeny more
nearly resembling paniculata than in the original cross. It was
found possible to cross A^ rustica X paniculata with A^ perennis,
although the cross of percnnis with either rustica or paniculata
failed.

Kolreuter concludes that the continued self-pollination of hy-
brids finally results in the re-appearance of the original parental
forms.

His ideas regarding fertilization are interesting. He thought,
as has been stated, that a plant was formed by the fusion of two
fluid materials of different sorts.

"since these materials are of different sorts, or in their essence are
different from each other, it is easy to comprehend that the strength ot
one must be different from the strength of the other. From the union
and commingling of these two materials, which occurs in the most inti-
mate and orderly manner, according to a definite relationship, there
originates another, which is of an intermediate sort, and which conse-
quently also possesses an intermediate, compounded force, sprung from
those two simple forces. . . . Upon this basis and its operative force,
which, according to the different kinds of its twofold fertilizing ma-
terial (Saamenstoff), must necessarily be different in the case of every
different kind of living machine, rests the gradual, progressive forma-
tion of the future plant, its particular organic structure, its specific
nature whereby it is distinguished from^ all others, and the proportion
of the fertilizing material demanded for a similar new reproduction
and, in a word, all those completed conditions (products) which are
required for the object to which it is designed." (1, p. 42.) . . . "All
the movements and changes, which from the embryo to the time of
flowering, take place in every such masterpiece of nature, appear to be
directed simply to the great work of reproduction. They all aim at
gradually liberating that compound material upon which they are based,
and at dividing it again into the two original ground materials; or,

48 PLANT HYBRIDIZATION BEFORE MENDEL

to speak more properly, to bring these latter themselves into a complete,
and, especially from the one side, into masses of unlike size than were
demonstrated from the preceding reproduction." (i, p. 43.)

Kolreuter's "Zweite Fortsetzung" to the 'A'orlauiige Nach-
richt," published in Leipzig in 1764, gives an account of 49 ex-
periments, of which 29 were distinctly crossing experiments, the
remainder being experiments involving the use of the plant's own
pollen, simultaneously with that of another species. The species
used in the crosses were as follows :

Species Number of crosses

Verbascum 4

Nicotiana 12

Dianthus 7

Hibiscus 2

Datisca 2

Mirabilis l

Leucojum l '

Of the twelve Nicotiana crosses seven, and of the seven Dian-
thus crosses four are compound.

Of the four Verbascum crosses, each with the same female, but
V. ith different male parents, it is reported that all were inter-
mediate, neither the one nor the other of the parents having the
preponderance.

Concluding in his own mind that the live tobacco forms rus-
tica, inajor, paniculata^ glutinosa^ and perennis, were simply va-
rieties of the same species, these, he says :

"l pollinated the past year (1762) reciprocally together, and obtained
through this manifold combination always the most complete capsules,"
and the plants obtained from these seeds, "held in all parts the mean
between their parents, and were just as fruitful as those could ever
have been." (p. 118.)

This fact was evidence to Kolreuter's mind that the five sup-
posed "species" were merely varieties of the same natural species.

Regarding crosses between {Nicotiana glutinosa X ^'- peren-
nis) and (Nicotiana glutinosa X ^^- major fl. alb.) Kolreuter
found that the plants were identical in type with those of the
reciprocal cross. Of the former he says fp. 120) :

"They did not come into full bloom, but one saw from their whole
appearance otherwise that they were as like those of the reciprocal ex-
periment, as one egg like another."

Of the second cross he remarks :

"So far as its resemblance is concerned, there was not the least differ-

PLANT HYBRIDIZATION BEFORE MENDEL 49

ence to be found between it and those of the reciprocal experiment."
(p. 120.)

Pursuing his conception that the activity of the pollen pro-
duced a quantitative effect depending upon the amount and char-
acter of the pollen employed in fertilization, Kolreuter instituted
a series of experiments with Nicotiana species. He found that N.
perennis^ pollinated with a small quantity of its own pollen, and
a much larger amount of glutinosa produced plants wholly per-
ennis, which had no character from glutinosa. Similarly A'', rus-
tica^ pollinated in part with its own pollen, and also with pollen
of paniculata and perenms, in equal proportions, produced
plants which were all ordinary rustica, and had taken nothing
from the other two. Another flower of N. rustica^ pollinated with
equal portions of its own pollen and pollen of N. perennis^ gave
plants which were ordinary rustica, without any trace of peren-
nis. A flower of A'^. rustica, pollinated with

"a very small quantity of its own pollen, and a much greater amount
of the pollen of paniculata," produced "six true hybrids, of precisely
the sort that one is accustomed to get from rustica 2 and paniculata S •"
(p. 122.)

Kolreuter investigated the probable nature of the stigmatic
secretion, whether it were the female fertilizing substance or not.
Removing the secretion from the stigmas of Nicotiana rustica
with a piece of blotting paper, he pollinated the surface with its
own pollen, and added the stigmatic secretion of A^ paniculata^
getting as a result six plants simply rustica. From another flower
of the same plant, pollinated with its own pollen, to which the
secretion from A^. mai. vulg. was added, he obtained four plants
of ordinary rustica^ with none of the characters of the other
species. A flower of A'', paniculata^ pollinated with its own pollen,
to which the secretion of rustica had been applied, gave four ordi-
nary paniculata plants. Upon the stigmas of a hybrid paniculata
? X rustica $ and another of rustica 5 X paniculata $ , polli-
nated with its own pollen, with the addition of the stigmatic secre-
tion of paniculata^ he obtained plants which all in appearance ap-
proached more the paniculata parent.

The result of all these experiments led Kolreuter to conclude :

"That one would almost sooner have reason to hold the female secre-
tion to be a mere innocuous conduction medium, than as a true fertilizing
material." (p. 128.)

50 PLANT HYBRIDIZATION BEFORE MENDEL

And again :

"Hence I believed myself, by virtue of the contrary outcome of my
experiments, to be justified rather in holding the oft-mentioned oily
secretion for a conduction medium, than to set it up as a true fertiliza-
tion substance (Saamen)."

In all, 49 experiments are detailed in Kolreuter's "Zweite
Fortsetzung," distributed over seven different genera, as follows:

Nicotiana 30 Datura 2

Dianthus 8 Mirabilis 2

Verbascum 4 Leucojum 1

Hibiscus 2

Of the 30 Nicotiana experiments, eight were species-crosses ;
nine, experiments with one or more kinds of pollen; seven, ex-
periments to determine the nature of the stigmatic secretion ; two
were F-^'s back-crossed with one of the parents, and four were
compound crosses. The pollen and stigma experiments have been
described in detail. The species-crosses involved the species pani-
culata^ glutinosa^ rustica^ transylvamca^ and major ft. albo. There
is nothing distinctly interesting in these crosses per se. In the case
of paniculata X glutinosa it is stated that the hybrid combined
the characters of the two parents in the most exact manner.
("Zeigte nebst den iibrigen Merkmalen offenbar an, dass sich die
Natur der $ mit der Natur der 5 auf's genaueste vereinigt haben
musste.") (p. 110.) Of the back-crosses on the Fj, of which two
are reported, in neither case is the number of the progeny suffi-
cient for generalization; being one, in the case of (A^. paniculata
X rustica) X paniculata^ and seven in the case of (A'^. pani-
culata X rustica) X rustica. The former cross is stated to have
resembled the original paniculata parent. In the latter case, all
seven more or less completely resembled the rustica parent, in
this respect resembling the behavior of the ten offspring of the
cross in Experiment 2 of the "Nachricht," [N. rustica X pani-
culata) X rustica, all of which throughout approached the rustica
parent, some more, some less. The compound crosses are not of
essential genetic interest.

Kolreuter reports the results of a curious experiment to deter-
mine the possible neutral character of the stigmatic secretion. In
1760, he placed upon the still clean stigmas of a Ketinia species,
"drops of different natural and artificial oils," deposited the pollen
therein, and awaited the result; the flowers all fell off unfertilized.

PLANT HYBRIDIZATION BEFORE MENDEL 51

(p. 140.) In the spring of 1763 the experiment was repeated with
a few other plants. When the stigmas of Nicotiana rustica showed
here and there drops of the secretion, he spread almond oil over
the surface with a fine brush, mixing it with the stigmatic secre-
tion, and spreading the whole over the entire surface, then apply-
ing a more than sufficient quantity of pollen. Pollination took
place successfully. Upon four other flowers, he used hazel-nut oil,
upon two, oil of jasmine, and upon four, linseed oil, with the
same result. With "distilled or artificial oils" no fertilization took
place, as also with animal fats and oils. The use of oil of both
sweet and bitter almonds, in the case of Verbascum blattaria, re-
sulted in fertilization. With pumpkins, however, the experiment
failed, although, as he says: "the oil of almond had penetrated
the ovary to over its half." (p. 142.) Kolreuter concludes, on
the basis of these experiments, that the essential fertilizing ma-
terial, issuing from the pollen grain, is the homogeneous fluid
oily substance, and not the granular material. The fact that this
portion of the pollen material, in his opinion, mingled freely with
the added vegetable oils, and still penetrated to the ovary, fertil-
ization following, was evidence, in his view, that both the fluid
portion of the pollen exudate and the stigmatic secretion were
alike oily substances, mixing freely with other oils of a vegetable
nature. Kol renter's assumption of an exudation under pressure
from the pollen grains of their contents lay of course at the basis
of this conclusion. He knew nothing of the growth of the pollen
tube, the character of which precluded any admixture of the con-
tents of the pollen grains with the stigmatic secretion or anything
else. However, considering the lack of morphological knowledge,
Kol renter's experiment may well be regarded as in every sense
scientific in spirit, and in the manner in which the conclusions
were drawn.

Of the eight experiments in crossing species of Dianthus, three
were species or variety-crosses, three were back-crosses upon F^
hybrids, one a self-fertilized Fj, and one a compound cross. From
the variations in type obtained in two back-crosses — (Dianthus
chinensis X carthusianoruni), and (Z). chinensis X carthusia-
noruin) X carthusianorum, — Kolreuter concludes that:

"The union of the fertilizing materials in the production of hybrids
in the first descending or ascending degree does not take place by far

52 PLANT HYBRIDIZATION BEFORE MENDEL

with the same regularity and uniformity, as in natural plants and the
first hybrid originally produced therefrom'' (p. 144.) (Italics inserted.)

This sentence is quoted in order to give as clear a picture as
possible of the attitude of a scientific mind of that time upon the
subject of the so-called "increase in variability" in hybrid genera-
tions after the first.

Kolreuter found that although the Chinese pink and the Car-
thusian could be successfully crossed, it was extremely difficult
to cross the Chinese with the garden pink.

"One will, among a hundred flowers, often scarcely find ten, which
are actually fertilized, and which contain one, or at most two to three
perfect seeds." (p. 150.)

An interesting genetic fact was ascertained in a cross between
Dianthus chinensis X ^« hortensis, in which the latter had
"double" flowers, and in Dianthus chinensis ft, simpl. X D. chi-
nensis ft. quadrupL, the result being the dominance of the mul-
tiple-petalled corolla in the F^. The statement is briefly made re-
garding the former cross (p. 152), with respect to the hybrid:

"its flowers were all reduplicate, and consisted commonly of 15-20
quite carmine-red leaves ; from which one plainly sees, that the pollen
of doubled flowers possesses the character of reduplicating simple ones
>vhich are pollinated with it."

This statement is extremely interesting because of the germ of
genetic thought which it manifests in the mind of Kolreuter. From
the second cross above mentioned, he obtained nine plants, among
which the most bore quadrupled — i.e., twenty-petalled flowers,
(p. 157.) Kolreuter remarks, "this experiment thus confirms that
one which has already been noticed above, p. 28, XL Expt."

The thing that immediately suggests itself to Kolreuter's mind
through these experiments is the opportunity offered for improv-
ing poor single flowers by crossing with doubles.

In the case of a wild plant growing in the neighborhood of
Calw, Dianthus plumarius^ Kolreuter remarks upon an extraor-
dinary condition found by him in the pollen of occasional plants
of the species, in which the pollen was of a dark-brown to purple-
red color, the grains being much smaller than natural. On polli-
nating a Chinese pink with this pollen he obtained no seeds, the
flower remaining open for ten days. But on pollinating with the
ordinary whitish-grey pollen, the plants closed in twenty-four

PLANT HYBRIDIZATION BEFORE MENDEL 53

hours, and he got as perfect seed-capsules and seeds as if he had
pollinated with the plant's own pollen.

Inasmuch as Kolreuter reports this type of pollen also as being
present in Saponaria officinalis and in Gypsophila fastigiata, it
seems probable that he was dealing with a pathological condition,
due possibly to a fungus infection. At jill events he reports that
the shedding of this pollen took place at the same time and in
the same manner as in these plants generally. It is interesting to
note his comparison of the abnormal pollen grains in question, in
respect to color, form and size with the smut of oats, and of other
grains. The second "Fortsetzung" closes with brief accounts of
crosses of Hibiscus manvhot with H. vitifolius and its reciprocal ;
Datura stramonium with D. taiula and its reciprocal ; Mirabilis
jalapa red-flowered X yellow-flowered and reciprocal ; and Leu-
cojum red-flowered X a white-flowered variety.

With respect to the Hibiscus cross, it is only of interest to note
the intermediac}^ of the four plants from each cross and their com-
plete resemblance to one another. In the Datura cross between
stramonium with white flowers, and tatula with violet flowers, the
hybrids from the two reciprocals, five and thre'e, respectively,
were completely alike. The purple color did not dominate. Kol-
reuter says :

"Their flowers had a whitish color playing a little into the violet;
the flower-tubes marked with five violet stripes, and the others sky-
blue." (p. 161.)

In the Mirabilis reciprocals, the color

"in the case of both the hybrid varieties was of mixed red and yellow.
The flowers played into orange-yellow." (p. 161.)

In the Leucojum red X white cross, the six hybrid plants all
had whitish-violet flowers.

Kolreuter's "Dritte Fortsetzung" is dated from Karlsruhe,
December 26, 1765. The memoir opens with a brief statement to
the effect that, after his success in 1762 at Sulz on the Neckar,
in the production of various hybrid plants, he had experienced
still greater success in 1763 at Calw, in obtaining, in addition
to fertile crosses with four species of Verbascum, several other
fertile combinations in the same genus, involving chiefly the re-
ciprocal crossing of the species native to the locality. The seeds
from these crosses were grown at Karlsruhe in 1764, and came

54 PLANT HYBRIDIZATION BEFORE MENDEL

into flower in the same year. Out of the 65 crosses reported in
the third 'Tortsetzung," the Verbascum crosses numbered 18, and
involved the species phoeniceum^ Thapsus^ lychnites, nigrum,
hlattaria and phlomoides.

All of the Verbascum crosses proved sterile. The crosses Lych-
nites fl. alb. X phoeniceum, Blattaria fl. flav. X nigrum, Blat-
taria fl. flav. X phoeniceum, Blattaria fl. flav. X Lychnites fl.
alb., Thapsus X nigrum, Lychnites fl. alb. X Thapsus, were
carried on reciprocally, and are interesting as being identical in
the reciprocal crosses, although their sterility showed them to be
species-hybrids rather than variety-crosses.

In describing the cross Verbascum blattaria fl. flav. X Verbas-
cum lychnites fl. flav., Kolreuter discusses the question, why one
or the other of the previously described hybrid plants should not
have sometimes arisen in the wild state, or, if such have not
arisen, wherein the obstacle lay for their production, in the case
of plants, which, for so many thousands of years, had lived in
proximity to one another. He remarks upon the fact that neither
in the older nor the later botanical writings is there a description
of any hybrid plant of this genus having arisen in the wild. The
essential reason, Kolreuter concludes, for the absence of such hy-
brids, lies in their total or very marked infertility. Concerning
Linnaeus' hybrid of Verbascum Lychnites X Thapsus, he ex-
presses no doubt as to the actual hybrid origin of the plant, in
view of the sterility of the plant, and the fact that the parents
had grown for years together in the same plot.

Kolreuter concludes then that the principle still holds, which
was laid down in the "Vorlaufige Nachricht," that, in the natural
state of things and under the ordinary set of circumstances, hybrid
plants are with difficulty produced or can be produced in nature.
Admitting, he says, that a botanist should have the fortune to
find a true hybrid plant in the field, the question yet remained
whether such an accident could have arisen in a region where
the natural conditions had remained entirely undisturbed directly
or indirectly. For, he says,

"true wilderness as it comes from the hand of Nature is one thing ; a
field, free, but in respect to a hundred things often very much altered
by the hand of man, is another." (p. 193.)

Kolreuter goes on to remark upon the apparent fact that the

PLANT HYBRIDIZATION BEFORE MENDEL 55

more rapid growth, the accelerated, earlier, and prolonged time

of flowering, the development of young shoots in autumn from

the roots, as well as from the stem, and a longer duration of the

plant, are to be reckoned among the general characteristics of

hybrids, (p. 193.)

"it is very difficult," he says, "to assume a valid reason for the en-
hanced vegetative vigor before flowering. The continuation of the
same after flowering, on the other hand, might be explained from the
fact that these plants cannot, like the natural ones, be exhausted and
impoverished through the development of the seed." (p. 194.)

With respect to the matter of increased rate of growth in hy-
brids, Kolreuter makes the following interesting and rather sur-
prising remark :

"l would wish that I or another were so fortunate as to obtain a
hybrid of trees, which, in respect to the utilization of their wood, might
have a great economic influence. Perhaps such trees among other good
characteristics would also have these, that, if the natural ones required
for their full growth, for example, a hundred years, they would reach
it in half this time. At least I do not see why they should behave
differently in this respect from other hybrid plants." (p. 194.)

Ten further crosses of Nicofiana are reported in the third
"Fortsetzung," but inasmuch as all but two are compound crosses,
they furnish no data of importance. The two remaining are ( A''.
paniculata X rustica) X rustica and (N. rustica X pciniculata)
X rustica^ i.e., back-crosses upon an F^, as they would now be
designated, or, in Kolreuter's terminology, hybrids in the descend-
ing degree, i.e., hybrids on the way toward a return to one of
the parents. However, no data are given of present genetic value.

Of the remaining crosses described, 29 are Dianthus crosses,
the species used being barhatus^ chinensis, brabetisis, carthusia-
norum^ superbus^ deltoides, armeria, plumarius, glaucus and vari-
ous forms of the garden pink, presumably also plumarius, but
referred to here as "'hortensis.'" The Dianthus crosses are distrib-
uted as follows :

Species and variety-crosses 12 F^ back crosses 5

Compound crosses 10 Fj selfs 2

Kolreuter remarks as to the cross Dianthus barbatus X chinen-
sis that, between the eighteen plants from this cross and those
from the reverse cross ("Fortsetz. der Vorlauf. Nachr.," p. 44),
there was to be found no noticeable difference. Reference to the
page in question, however, gives the cross there reported as Dian-

56 PLANT HYBRIDIZATION BEFORE MENDEL

thus chinensis y^carthusianorum^ so that Kolreuter is apparently
in error in his citation. Of the cross Dianthus hortensis \ chinen-
sis, three plants were produced. Kolreuter states:

"Throughout, there was, between all these plants and those of the
reverse cross, both in what pertained to the whole external structure,
as well as also in respect to their inner characteristics, no essential
difference to be found." (p. 209.)

The reciprocal cross is reported, not in the third "Fortsetzung,"
but as Experiment 40 in the second. In regard to a cross of Dian-
thus chinensis X ^- superbus, a carmine-red form with double
flowers, it is stated of the hybrids, twenty in number, that :

"Throughout, these plants held in all details the mean between the
female and male, except that they had bloomed earlier and longer."
(p. 212.)

Most of the hybrids were infertile as to their pollen, even when
abundantly close-pollinated. The egg-cells showed on the other
hand a limited amount of fertility, giving, when open-pollinated
from other species in the neighborhood, not seldom capsules with
generally two to four seeds, and when hand-pollinated from these,
six to eight seeds. So far as the doubling of the petals is con-
cerned, it may be assumed that the hybrids were on the whole
intermediate, since, as Kolreuter says:

"One sees plainly that the female contribution in respect to this cir-
cumstance is of a like activity and character with the male." (p. 213.)

Of a cross Dianthus hortensis X harhatus it is stated (p. 216),

"it showed quite plainly, that it had taken an equal share from both
natures."

From a cross between a double Dianthus chinensis and a native
wild species, D. armeria, Kolreuter obtained ten plants, of which
he says :

"Among all these hybrids, there was not a single one with simple
flowers, but all either with double, even more strongly reduplicated, or
quite doubled very decorative flowers ; a circumstance which again places
out of all doubt the activity of the female in respect to this point."
(p. 222.)

These hybrids were in the highest degree infertile as to the
egg-cells, although exposed throughout the summer to pollina-
tion from various other natural species in the neighborhood, and
even when pollinated most carefully by hand, with pollen from
the male or the female parent or from other pinks, setting not a

PLANT HYBRIDIZATION BEFORE MENDEL 57

single capsule. Of a cross between a Dianthus plumarius, which
Gmelin had brought from Siberia, a plant with snow-white fringed
petals, and D. chinensis^ a plant with single flowers, unf ringed,
scarlet-red, with black-red circle, it is stated :

"in size, as generally in all details, they showed exactly the mean be-
tween those of the male and female." (p. 224.)

From a cross between Dianthus harhatus and chinensis selfed,
three plants were produced, all different from one another. To
Kolreuter's mind the matter is regarded thus :

"So much in the meantime is quite clear, that the self-fertilization of
such hybrids must go on dissimilarly, and not in an orderly manner,
since it even appears as though thereby sometimes a basis were laid for
misbirths, as is manifested by, the dwarf stature of the second plant of
the present, and of the two hybrids of the thirty-seventh experiment."
(P- 233.)

Kolreuter states that a no less amount of difference showed
itself among a few plants of the reciprocal cross, to which he
refers as being reported in the second "Fortsetzung," Sec. 26,
p. 106. The reference cited, however, is to the selling of a cross
between Diaiithus chinensis X carthusianorum.

Kolreuter also states (p. 236) that he had previously taken the
complete similarity of hybrids in reciprocal crosses, as an infal-
lible indication of the equilibrium existing between the two fer-
tilization elements, but that one must take this principle in a
limited sense. The similarity of reciprocal crosses proves incon-
trovertibly, that in both cases throughout, the same proportion
existed in the mixture of the fertilization elements, but not at
all that in every particular case, in respect to mass or activity,
an equal amount of each is used in fertilization. As for example,
in crossing a blue with a yellow color, a third or green color is
produced in a certain definite degree, whether the blue is mixed
with the yellow or the yellow with the blue.

"This green color," he says, "will not exactly, however, on this ac-
count, hold completely the mean between the two ground colors, and
consequently be distinguishable from that which comes out when one
has mixed ten parts of each with the other. In this connection one must,
however, pre-suppose that both ground colors are of like activity, for
if, for example, the yellow were by one-tenth more active than the blue,
yet nevertheless in the given case, irrespective of the unlike proportion
in the mass, a medium color would come out, to which each of these
ground colors according to its activity contributed equally much."
(P- 237.)

58 PLANT HYBRIDIZATION BEFORE MENDEL

The remainder of the crossing experiments reported upon in
Kolreuter's third "Fortsetzung" are as follows: A cross between
Datura ferox ft. alb. and D. tatula fl. viol., a back-cross of Mira-
bilis jalapa (yellow), upon M. jalapa red X yellow. A reciprocal
cross is reported between Cheiranthus (Matihiola) incana and
Ch. annuus, between Sida cristata minor X major; Cucurbita of
a small round variety with few, small seeds, by a large Cucurbita
pepo, and a cross between Aquilegia vulgaris X canadensis and
its reciprocal.

In the Datura cross, involving purple flower-color in D. tatula,
the flowers of the hybrid are reported as being "whitish-violet."
The Mirabilis back-cress is reported as giving the yellow color
in a stronger degree than in the ¥^. The Cheiranthus (Matthiola)
cross is interesting because of the genuine genetic purpose for
which it was undertaken.

Kolreuter remarks:

"since the essential difference which one believes to exist between
winter and summer stocks always seemed to me suspicious ; I therefore
concluded to completely decide this hitherto doubtful matter through
the experiment of crossing." (p. 200.)

From these crosses, he raised in 1764, twelve plants from the
first, and six from the reciprocal cross. These were in all respects
like one another. Their intermediate character showed itself espe-
cially in the fact that they began to bloom earlier and more
vigorously than the winter stocks are accustomed to do in the
first year, and on the other hand brought their flowers out
later, and not in the complete numbers that the summer stocks
are accustomed to do.

The Sida cross is reported as giving a hybrid intermediate in
color, form, and size of all the parts, between the two parents.
The Cucurbita cross likewise gave a complete intermediate.

An interesting discussion follows of the sensitivity of the sta-
mens in flowers of Opuntia, Berberis, and Cistus. The last pages
of the third "Fortsetzung" (252-63) are taken up with a discus-
sion of further experiments on the pollination and fertilization
process.

"since there are some people," he says, "who have brought into doubt
the organic structure of the pollen, assumed by me in the 'Vorlauf.
Nachr.' Sec. 5, I therefore hold it as my duty to help them out of their
dream in this respect, and to give a somewhat closer explanation of this
matter." (p. 252.)

PLANT HYBRIDIZATION BEFORE MENDEL 59

Kolreuter then proceeds again to a detailed description of what
is now known to be the exine. The fire-lily {Lilium bulbiferum)
is taken as the type for discussion. The pollen grains of this
species, under "moderate magnification," appear, as he says, to
have a shagreen-like surface, as though covered with small pa-
pillae. With a "stronger magnification, one sees, instead of the
papillae, a net-like structure." By pressing the dry pollen grains
gently together between two thin sheets of mica, so that the
material contained in them is expelled, and bringing them under
the microscope, he says :

"One will see their empty and' transparent skins entirely interwoven
with vascular or nerve-like threads, which are bound together, and
represent an irregular net with unlike angular 'eyes.' These fibres, how-
ever, never cut through one another, but make, even where they come
together, no knots, but anastomose as it were amongst one another; and
therein is this net-like structure wholly different from an actual net."

(P- 253-)

Such is Kolreuter's final description of the ridges and reticula-
tions on the exine, which he took for a sort of fibres penetrating
its tissue.

If these fibres therefore, he says, represent sap or air-vessels,
the sap or air must have free access or passage from one branch
to another. Other species of Lilium are stated to have the same
structure, as also the pollen of Agave americana and many species
of Orchis. From observation of these and others he concluded
that, in a very large number of species, on the pollen, which on
account of its small size and other characteristics showed scarcely
a trace of "organic structure," there were still present similar
structures to those in the species indicated. The inner coat of the
pollen grain is described so far as it shows itself in the form of
the pollen tubes emerging through the germination pores. The
germination of the pollen grains, so far as Kolreuter observed it,
or was able to follow it, is described as follows. In the case of
Scabiosa succisa^ he gives the following 'account : The white,
smooth, roundish pollen grains, as soon as they are placed in
water, give off a great quantity of a pale, sulphur-yellow oil,
gradually swell with the absorbed water, and soon thereafter,
from three equidistant weaker places in the wall, send out, ordi-
narily, three conical, membranous plugs, which are immediately
to be distinguished from the outer, hard, and opaque shell of

6o PLANT HYBRIDIZATION BEFORE MENDEL

the pollen grain by their transparency, and their uncommonly
thin and uniform substance. As these plugs or horns gradually
arise, one sees also the absorbed water, together with a part of
the granular material, press into them and stretch them to burst-
ing. They scarcely reach a length amounting to the small diam-
eter of the pollen grain, before a slit appears at one side of the
base, and in a moment the mixed material, which has already
entered the plug, pours forcibly out of the slit, the pollen grain
noticeably shrinks together, and the remaining two plugs with-
draw almost wholly into the pollen grain, or at least noticeably
diminish in size. Sometimes, instead of the three horns or plugs,
only two or even only one makes its appearance. The process is
similarly described for the pollen grains of Dipsacus fullo?iU7n,
Kiiautia orientalis, Linnaea borealis^ as also for species of Gera-
nium. Kolreuter accurately describes the germination-pores of the
pollen grains as thin places in the coat. If his observations require
correction, it is nevertheless well to note their accuracy within
their own category, and within the observational limits then pos-
sible.

The third "Fortsetzung" concludes with an extremely careful
and interesting natural history account of the sequence of events
in the pollination of the stigmas of Hibiscus manihot.

"At about nine in the morning on a clear, warm day," (of July 1759),
he says, "a flower of the species named opened. Its four carmine-red
pistils stood upright but close together. The whitish anthers opened
gradually, and showed in part their pale, sulphur-yellow and still
opaque pollen grains. The knobby dark-red stigmas, which hitherto had
remained still quite dry, began, from their long, fine and pointed
papillae, to secrete the female moisture, and acquired thereby a glisten-
ing, as though they had been painted over with a varnish, or had been
saturated with a fine oil. I thereupon placed upon them by means of a
delicate brush a limited quantity of the still opaque pollen grains.
Soon thereafter these acquired also a glistening appearance, and together
with this, a transparency which they had previously not yet had, be-
neath their dull appearance. The glistening of the stigmas increased ever
more and more, from the moisture which heaped itself upon them ; and
the pollen grains borne upon them became, finally, one after the other,
so clear and transparent, that the purple-red color of the papillae
lying beneath them appeared very plainly through them. During the
time, however, when they reached the highest degree of ripeness, they
already began to diminish a little in size. Gradually they lost also
their transparency again, became ever smaller, and appeared imper-
ceptibly to acquire wrinkles. At last they became very small, shrunk
gradually together, lost all transparency and dried out. All these changes
took place also at the same time with the other pollen grains remaining

PLANT HYBRIDIZATION BEFORE MENDEL 61

upon the knobs of the stigmas. In the meanwhile, the stigmas had grad-
ually withdrawn from one another, drawn outward, and finally turned
back on their outer halves against the base of the flower. Their glisten-
ing effect disappeared again gradually with their moisture, and they
became finally covered by the closing and wilting petals." (p. 262.)

The above is given in full for the sake of its natural history
interest, as a type of observation none too common, and for the
sake of showing what Kolreuter's spirit was at its best. The
graphic, narrative, and even poetic style of the account should
render it a classic among natural history observations. This closes
an attempt, extensive and somewhat detailed, to give as complete
and exact a presentation of the Kolreuter material as possible.
If the account is somewhat disproportionately extended, it is
nevertheless desirable to have the data from Kolreuter's slightly
difficult and sometimes a trifle obscure German rendered as ac-
cessible as possible in English.

BIBLIOGRAPHY

1. Kolreuter^ Joseph Gottlieb.

(a) Vorlaufige Nachricht von einigen das Geschlecht der
Pflanzen betreffenden Versuchen und Beobachtungen,
nebst Fortsetzungen 1, 2, und 3 (1761-66). W. Pfeffer,
in Ostwald's Klassiker der exakten Wissenschaften, No.
41. Leipzig, 1893.

(b) Historic der Versuche iiber das Geschlecht der Pflanzen;
No. 17 in Mikan's Opuscula Botanici Argumenti. Prag,

1797-
Note: From 1770-1775, thirty-one articles by Kolreuter, chiefly on zool-
ogical subjects, appeared in the "Novi Commentarii Academiae Scientiarum
Imperialis Petropolitanae" (Vols. XV-XX, inc.). Of these, one only (in
Vol. XX) was upon hybrid plants. In the "Acta Academiae Scientiarum
Imperialis Petropolitanae," 1777-1782, appeared seven articles by Kol-
reuter on hybrid plants, and in the "Nova Acta" of the same Academy,
1783-1796 (Vols. I, III, XI, XII, XIIl), five further papers were published
on the subject of plant hybrids. Unfortunately, it has been impossible
to secure access 'to the St. Petersburg papers of Kolreuter in time for
their inclusion in the present volume.

2. Sprengel, Christian Konrad.

Das entdeckte Geheimniss der Natur Im Bau und in der Be-
fruchtung der Blumen. (1793), ed. Paul Knuth. In Ost-
wald'^ Klassiker der exakten Wissenschaften, No. 48, 4 vols.
Leipzig, 1894.

CHAPTER 111

9. Miscellaneous Experiments Regarding Sex in Plants.

CAMERARIUS and Kolreuter represent the two chief land-
marks in the history of plant breeding and genetics up to
1766. While these were the only investigators whose direct
contributions to our knowledge of sex in plants, or of heredity
in the plant organism, were extensive or fundamental, it is of
interest to know that the hrst person who is reported to have
actually crossed plants artificially, was an Englishman named
Thomas Fairchild, who, according to Richard Bradley, Professor
of Botany in Cambridge University, 1724-1732, (1) in 1719
crossed Dianthus barbatus L. ( Sweet-William), with pollen of
the Carnation {Dia?ithus caryophyllus L.). The cross in question
was still known in gardens one hundred years later as "Fair-
child's Sweet-William." Nevertheless, as Focke says (2, p. 430):

"This success in artificial fertilization was never utilized for science,
nor does it appear to have given gardeners any stimulus to further
investigations."

It is possible that the first conception of the function of the
stamens of the flowers as the source of the male fertilizing ma-
terial is ascribable to an Englishman, Sir Thomas Millington
(1628-1704). Millington was a physician by education, B.A.,
Cambridge, 1649; M.A., 1657; Fellow of All Souls College, Ox-
ford, 1659. He is known as having taken part in the scientific
meetings which gave rise to the Royal Society, of which he was
an original member. He became Fellow of the College of Physi-
cians in 1672, and was Sedleian Professor of Natural Philosophy
at Oxford from 1675 to his death in 1704.

In a lecture on the anatomy of flowers, said to have been read
by Nehemiah Grew before the Royal Society, November 6, 1676,
the latter is quoted as follows:

Plate XX. Sir Thomas Millington, 1628-1704. Sedleian Professor of Natural History of
Oxford (1675-17C4).

64 PLANT HYBRIDIZATION BEFORE MENDEL

"In discourse hereof with our Learned Savilian (Sedleian), Professor
sir Thomas Millington, he told me, he conceived, That the Attire
(Stammens) doth serve, as the Male, for the Generation of the Seed.
I immediately reply'd That I was of the same Opinion."

The date of this supposed lecture was six years earlier than
Grew's "Anatomy of Plants" in 1682, in which the statement is
repeated (4b,' 171) in almost identical words, and eighteen years
before the publication of Camerarius' "De Sexu Plantarum Epis-
tola." ^ However, the lack of experimental data to support the
conclusion gives the incident historical rather than scientitic value,
except for whatever influence it may have had upon later investi-
gations in the subject.

Richard Bradley's conceptions on the subject of sexuality in
plants seem, according to his own statement in his "New Improve-
ments of Planting and Gardening," to have been derived from a
certain Robert Balle, likewise a member of the Royal Society. It
appears from Bradley's account, that he derived further sugges-
tions in the matter from Moreland's communication to the Royal
Society in 1703. (8.) Bradley's account follows:

"The first hint of this secret [that every plant contains in itself male
and female powers] was communicated to me several years ago by a
worthy member of the Royal Society, Robert Balle, Esq. ; who had this
notion for above thirty years, that plants had a mode of generation

^ The statement that Grew delivered an address before the Royal So-
ciety, November 6, 1676, or, according to Logan, November 9 (p. 64),
requires modification. A search through the volumes of the Philosophical
Transactions of the Royal Society for the years 1676-77 reveals no address
by Grew on the subject, or containing the quotation referred to. An in-
quiry of the office of the Royal Society was responded to by a letter from
the Assistant-Secretary (October 31, 1927) as follows:

"The supposed quotation from a paper by Grew seems certainly at
fault. We trace no such paper in the Philos;;phical Transactions. There
was no meeting on November 6, 1676. There was a meeting on Novem-
ber 9, and at that meeting Grew gave a Lecture on Flowers. This seem»
never to have appeared in print before the publication of his 'Anatomy
of Plants' in 1682. But the lecture was ordered to be 'registered' and
we have it copied in MS in vol. 5 of our 'Register Book' series. We have
glanced through the copy page by page (there are 10 pages of it) but
we failed to trace the statement you quote : 'In discourse with . . .'
On the face of it we should say that that statement appeared only in
the published volume of the 'Anatomy of Plants,' 1682."

In a previous letter (October 8, 1926), from the office of the Royal
Society, it is stated: "All the Society did in the present case of Grew's
communications was to desire him 'to cause them to be printed together
in one volume.' " The first authentic reference, therefore, to the matter,
must be taken to be Grew's publication in his "Anatomy of Plants," pub-
lished in 1682.

PLANT HYBRIDIZATION BEFORE MENDEL 65

somewhat analogous to that of animals. The light which I received from
this gentleman was afterward further explained by another learned
gentleman of that Society, Mr. Samuel Moreland, who in 'Philos, Trans.,'
Number 287, Anno 1703, has given us to understand how the dust of
the Apices in flowers [i.e., the male sperm] is conveyed into the uterus
or vasculum seminalis of a plant, by which means the seeds therein
contained are impregnated. I then made it my business to search after
this truth, and have had good fortune enough to bring it to demonstra-
tion by several experiments; since which, a gentleman of Paris had
printed something of the same nature, in the 'Hist, de I'Acad. des
Sciences,' for the year 1711 and 1712, which were published about two
years ago."

Bradley's account of the Fairchild crossing experiment is as
follows :

"Moreover, a Curious Person may, by this knowledge, produce such
rare Kinds of Plants as have not yet been heard of, by making choice
of two plants for his Purpose as are near alike in their parts, but
chiefly in their Flowers or Seed Vessels; for example the Carnation and
Sweet-william are in some respects alike, the Farina of the one will
impregnate the other, and the Seed so enliven'd will produce a Plant
differing from either, as may now be seen in the Garden of Mr.
Thomas Fairchild of Hoxton, a plant neither Szveet-William nor Carna-
tion, but resembling both equally, which was raised from the Seed of
a Carnation that had been impregnated by the Farina of the Sweet-
William." (pp. 20-3.)

Two years earlier, Bradley himself (1. pp. 20-5'), had removed
the anthers from the flowers of twelve tulips which he had planted
in a remote place in his garden, and had discovered that they pro-
duced no seeds, while some four hundred tulips, planted elsewhere
in the garden and left intact, produced seeds freely.

The account of the experiment is given as follows :

"l shall now proceed to what I call the Demonstrative Part of this
System. I made my first Experiment upon the Tulip, which I chose
rather than any other Plant because it seldom misses to produce Seed.
Several years ago I had the Conveniency of a large Garden, wherein
there was a considerable Bed of Tulips in one Part, containing about
400 Roots ; in another Part of it very remote from the former, were
Twelve Tulips in perfect Health. At the first opening of the twelve,
which I was very careful to observe, I cautiously took out of them
all their Apices, before the Farijia Fecundans was ripe or any ways
appear'd. These Tulips, being thus castrated, bare no Seed that Sum-
mer, while on the other hand every one of the 400 Plants which I had
let alone produced seed. . . .

" 'Tis from this accidental Coupling that proceeds the Numberless
Varieties of Fruits and Flowers which are raised every Day from Seed.
The yellow and black Auricula's which were the first we had in Eng-
land, coupling with on^ another, produced Seed which gave us other
varieties, which again mixing their qualities, in like manner, has af-
forded us by little and little the numberless Variations which we see

66 PLANT HYBRIDIZATION BEFORE MENDEL

at this Day in every curious Flower Garden; for I have saved the
Seeds of near an hundred plain Auricula s, whose flowers were of one
Colour, and stood remote from others, and the Seed I remember to
have produced no Variety; but on the other hand, where I have saved
the Seed of such plain Auricula's as have stood together and were dif-
fering in their colours, that Seed has furnished me with great Varieties,
different from the Mother Plants."

In 1731, Philip Miller, in the first edition of his "Gardeners'
Dictionary" (7), reported upon a repetition of Bradley's experi-
ment with tulips, and also upon an experiment with spinach, in
which plants of the two sexes, grown apart, resulted in the pro-
duction of seeds devoid of embryos.

Miller (1692-1771), was Governor to the Apothecaries' Com-
pany, from 1722 to 1770, at the Chelsea Gardens near London.

In 1724, he published "The Gardeners' and Florists' Diction-
ary, or a Complete System of Horticulture," of which Linnaeus
said, "non erit lexicon hortulanorum sed botanicorum." The work
went through eight editions during his lifetime. It is said of it
that while before its appearance not more than a thousand species
of plants were in cultivation, at his death there were more than
five thousand. He was a correspondent of Linnaeus, who visited
the Chelsea Garden several times, when in England in 1736. The
seventh edition of "The Gardeners' Dictionary," in 1759, con-
tained twice as many plants as the first edition, and adopted the
nomenclature of Linnaeus. The account here given of Miller's ex-
periment is taken from the 1759 edition, from the chapter (un-
paged) entitled "Generation."

"I shall therefore conclude with mentioning a few Experiments of
my own, which I communicated to Dr. Patrick Blair, which he improved
as Proof of his opinion of Effluvia, and Mr. Bradley also, as a Proof of
the Fari?ia entering the Uterus in Substance, and leave the curious En-
quirer to determine on that Side of the Question, to which Reasoning
and Experiment shall influence him.

"I separated the male Plants of a Bed of Spinach from the female ;
and the Consequence was that the Seed did swell to the usual Bigness,
but when sown it did not grow afterwards ; and searching into the Seed
I found it wanted the Punctum Vitae (or what Geoffrey calls the
Germen).

"I set twelve Tulips by themselves, about six or seven yards from
any other and, as soon as they blew, I took out the Stamina (with their
Summits) so very carefully, that I scattered none of the male Dust;
and about two days afterwards I saw Bees working on a bed of tulips,
where I did not take out the stamina ; and when they came out they
were loaded with the farina or male dust on their legs and bodies;
and I saw them fly into the tulips where I had taken out the stamina,

Plate XXI. Philip Miller, 1691-1771.

68 PLANT HYBRIDIZATION BEFORE MENDEL

and when they came out, I found they had left behind them sufficient
to injj)regn^te those flowers, for they bore good ripe seeds which after-
ward§; grew."

In 1739 appeared a small memoir of thirteen pages, by James
Logan, "Supreme Justice and President of the Provincial Council
of Pennsylvania in America." This memoir, published in Latin
at Leiden and entitled "De Plantarum Generatione Experimenta
et Meletemata," contains an account of the author's experiments
on the fertilization of Indian corn, and his conclusions on the
subject of plant fertilization in general. After a description of the
plant, and its manner of flowering, he says:

"On -the ear appear very beautiful ranks of grains, generally eight,
often even ten, and more rarely indeed twelve, and even sixteen I have
seen. In any such row, the grains are 40 more or less, which in their
rudimentary stage, when the spike is still tender, may rightly be called
ova, and upon each ovum arises a slender, delicate, white filament which
is also hoUow, and is like a silken thread. These individual threads
break through seriatim, between the rows, from the beginning to the
ulterior extremity, where, protruding themselves from the leaves which
protect the whole ear in a bundle, they appear prominently in the air,
in color more often in this prominent part whitish, sometimes indeed,
according to the various kind of plant, yellowish, reddish, or purplish ;
andi-these filaments, as, I suspected, are presently to be understood as
the^true styles of the ova."

The. experiment in fertilization is described as follows :

"Therefore, setting about experiments with this plant, in my urban
garden, 40 feet in width and about 80 feet in length, from the different
corners, having heaped up little hills, according to the method of sow-
ing, in the latter part of the month of April, I planted four or five
grains of seed (in each). At the beginning of August when the plants
had grown to their proper size, and the tassels (cirri) on the summit,
and the ears (spicae) on the stalk, had fully appeared, I cut off from
one hill all these tassels from within : in others, however, the tassels
being intact, I cut off the whole bundle of filaments or styles from -.
certain ears, having gently freed them from the enclosing leaves, and
covered them again, and from others cut one-fourth, and others left /
intact. Another ear, before the bundle (of styles) should get to the
light, I gently wrapped in a light, soft cloth of Indian or Chinese linen,
called by us 'muslin,' and so loosely that not the least injury should
happen to the vegetation, so that, on account of the lightness of the
cloth, the ear should enjoy the benefit of the sun, the air and the
showers, but that on account of the woolly cloth it would be exposed
to no approach of the pollen. Four hills I left whole and intact, and
as many of the others also as possible, in that condition which I have
stated, I permitted to come to the time of maturity, (pp. 8-9.)

"Towards October, it was seen that in the first hill, which had been
completely detasselled, although the ears were satisfactory to the eye,
not a single grain was matured, except in a single ear of greater size,

PLANT HYBRIDIZATION BEFORE MENDEL 69

which projected higher up, upon a stalk facing the adjoining hill, on
the side toward the prevailing winds. On this ear some twenty grains
matured.

"in those (ears) from which I had removed the styles," he states,
"exactly as many seeds were found, as I had left styles intact; in those
I had wrapped in cloth, not a single one. In the void or empty ova
nothing except a dry skin was seen." (p. 9.)

Plate XXII. James Logan, 1674-1751.

70 PLANT HYBRIDIZATION BEFORE MENDEL

Logan therefore concludes :

"From these experiments, instituted and carried out by me with the
utmost accuracy, as also from several by others, it holds that this
pollen, evolved from the anthers, is the true masculine semen, and is
most clearly entirely necessary to the fecundation of the uterus and
seeds, which fact nevertheless all the centuries concealed up to ours."

(P- 9.)

The care with which the experiments were carried out, is suffi-
ciently attested by the remark (p. 16) :

"After these experiments were undertaken, I scarcely permitted myself
to be absent from these investigations, either through the state of my
health or by business."

Millington is referred to in the following words:

"Worthy is therefore that Discoverer of this Arcana of Nature, whose
memory should be perpetually celebrated. He seems to have been Thomas
Millington, an English Knight, Savillian professor in his time before or
about the year 1676. For thus reported Grew in an address before the
Royal Society, held the 9th of November of that year. Malpighius in-
deed, so far as I know, nowhere thinks of any use for it (i.e., the pollen).
Grew himself suspected the pollen to be necessary for fecundation, but
not that it entered the uterus ; but twenty or more years after him,
Samuel Moreland, also an Englishman, affirmed that it descended to
the uterus itself, through the canaliculi of the style." (p. 6.) (See
antCi pp. 62-64.)

10. Gleditsch's Pollination Experiments with the Palm.

In 1751, Johann Gottlieb Gleditsch, Director of the Berlin Bo-
tanical Garden, published an account of an experiment in the
crossing of a species of palm {Chamaerops huinilis), of which
Sachs says in his "History of Botany" :

"This treatise, in point of its scientific tone and learned handling of
the question, is the best that appeared between the time of Camerarius
and that of Kolreuter." (9.)

Gleditsch's account, as reported in the "Histoire de I'Academie
des Sciences et Belles Lettres," 1749, begins as follows:

"The theory of sex of plants, which," he says, "has been so long and
vigorously debated by modern naturalists, is at present supported upon
incontestable foundations, which are experience and reason. Things which
the greater number of physicians regarded formerly as ridiculous and
imaginary are proved today by the most simple experiments, and with
so much evidence that there no longer remains the least place for all
the objections capable of being formed against this system, or for all
the jests with which it could be loaded." (5a, p. 103.)

It is not, he adds, that there are not more who still doubt the

PLANT HYBRIDIZATION BEFORE MENDEL 71

existence of true sex in plants, "but their number is very small,
and their arguments do not appear to merit any response."

"Leaving all these disputes to one side," he continues, "I have only
been interested in acquiring a full proof of this theory ; and to this end,
for several years, I have made experiments on plants of every sort, and
I have had the pleasure of seeing the truth discover itself to my re-
searches, and especially in later years, with perennial plants, trees of the
same natural species (the sexualists call them vulgarly dioecious), of
which one carries the male flowers, while the other, its companion, which
is quite a different one, carries only the female flowers." (5a, p. 103.)

Of these he mentions, (p. 104) the genera Ceratonia, Pistacia,
Terebinthus and Lentiscus, and "cette espece de Palmier dactyli-
fere qu'on nomme vulgairement Chamaerops, Chameriphesy

In the garden of the Academy of Sciences in Berlin, he com-
ments, the difference in sex in the flowers of trees had long been
noticed, the gardener himself having remarked it for more than
twenty years. The latter was, however, unable to discern the cause
of sterility in the plants. The simplicity of mind obtaining in re-
gard to the matter at the time is evidenced by Gleditsch's remark,
that the gardener was greatly surprised at the appearance of the
perfect fruits of the terebinth {Pistacia terebinthus), because he
had not thought of this, that the simple sprinkling of the powder
of the anthers was sufficient to effect its production. His surprise
doubled especially, when, from these fruits, either planted of
themselves in the ground or planted expressly with care, he saw
arise, a little afterwards, the finest plants in the world, (p. 104.)

The attempt is mentioned of Prince Eugene of Austria, during
the last years of his life, to secure the artificial pollination of the
palm, a matter of which he had read descriptions. To this end,
he had palm trees of the different sexes and of considerable size,
sent to his garden at Vienna, but the palms perished in the space
of a year, without flowering.

The palm at Berlin upon which Gleditsch determined for his
experiments, was a pistillate tree, which was, as he says, possibly
more than eighty years old, "and certainly the largest of all those
of its species which are found today in the gardens of Germany."
According to the testimony of a man said to be of note, and then
in his sixty-sixth year, the tree in question was formerly in the
Royal Garden at Berlin, and had been seen by the person referred
to in its earliest days. During this entire time the tree had borne

72 PLANT HYBRIDIZATION BEFORE MENDEL

no fruits, nor later in the Botanical Garden, according to the
gardener,

"and for my part," Gleditsch adds, "I have never remarked, among the
flowers which fall every year from this palm, any perfect fruit; still
less have I been able to observe any which encloses a fertile seed." (p.
io6.)

In the spring of 1749, Gleditsch (p. 106) was able to obtain,
from the botanists Ludwig and Boehmer at Leipzig, flowers of a
male plant growing there in the garden of a certain Caspar Bose.
Gleditsch states as follows :

"I received them in the spring of 1749, during the days which were
already very warm. The heat of the sun had completely withered and
spoiled the packets of stamens, and the greater part of the powder had
escaped from the seminal vesicles. I collected in a small spoon a part of
this powder, which was spread for the time on the paper with which the
box was lined on the interior." (p. 106.)

The journey from Leipzig had taken nine days, during which
time the pistillate palm at Berlin, on account of the heat, had
entirely finished flowering, so that there remained only a very
small number of flowers at the tips of the branches; in addition
to which, however, unexpectedly, a small cluster of new flowers
bloomed late. The pollen, which had escaped from the anthers and
adhered to the paper, was spread upon the pistillate flowers, and
the packet of already mouldy stamens was applied to the flower
cluster that had bloomed late.

"This sprinkling of the fecundation powder having been done, the
fecundation had the success I would have expected; the vegetati n-
bladders swelled in great number, and became filled with a fertile setting
of seed, suitable for further propagation; these became veritable little
eggs." (p. 107.)

"These little eggs or seeds ripened in the fruits the last winter, and
having been planted in the ground at the beginning of the spring of 1750,
plants have come from them conformable to their origin, that is to say,
little palms, which testify in an incontestable manner that vegetable fe-
cundation has been fully accomplished." (p. 107.)

Another pollination experiment was made in 175'0. Another
packet of male flowers was obtained from Leipzig. Of this experi-
ment, Gleditsch states :

"Its particles have promptly penetrated the stigmas of our female
palm, and have the efficacy of fecundating a great quantity of fruits or
dates, of which I have presented the clusters to the Academy in order
to submit them to its examination." (p. 107.)

"This so simple attempt at the artiKcial fecundation of our palm makes

PLANT HYBRIDIZATION BEFORE MENDEL 73

it evident that the greater part of the difficulties which the botanists
make a display of in their theories, which very often they invent, in
relation to the fecundation of vegetables, have almost no reality, and,
if they had, it would necessarily require that the greater number of
plants remained sterile." (p. 108.)

A third experiment in the fertilization of the palm, was again
undertaken in 1767. The species of palm used in the experiments
was, according to Gleditsch's statement, the same individual as
used in the two previous ones. (p. 7.)

"The female palm which we preserve in the Royal Botanical Garden is
very old, and of fine appearance, without having ever borne dates up to
the years 1749 and 1750, when I fertilized it for the first and second
times with the powder of the flowers which I had let come from Leipzig
by post. I made report at the same time to the Academy of these two
experiments, and I produced by means of the dates, perfectly ripe, young
palms, which exist still in the garden." (p. 7.)

After describing the pollination of the palm by means of the
transportation of the pollen by air currents, and the hand-
pollination of the date in oriental countries, which, he says,
"has taken place in these countries since men inhabit them and
cultivate them," he remarks:

"This does not prevent the savants from putting the question nowa-
days of whether the thing is possible, and the fact is real." (p. 6.)

"Let one separate the male palms from these female ones," he con-
tinues, "of which I have said above that the proximity of the males was
absolutely necessary for them for fertilization ; one will infallibly see
happen what took place at Berlin with respect to our female palm, since
the time of the late King Frederick I, to wit, that this tree, deprived of
its male, had remained in perfect sterility since, and that its fruits have
not reached maturity." (p. 6.)

"No one indeed," he says, "will ever confound the unfertilized debris
which our palm produced, every year, and which I place here by the side
of the effect of fecundation, with these perfect fruits, and especially with
that which has served to produce a young palm which derives its extrac-
tion from the first." (p. 7.)

The pollen for the third pollination experiments was sent from
Karlsruhe, a distance of eighty miles. Referring to the custom in
the orient, of hunting for the male trees, from which the inhabi-
tants bring in clusters of the staminate flowers to hang beside
the female flowers, he makes the statement that the male flowers
remain sometimes fifteen days or three weeks on the road before
being used for pollination.

Before undertaking the first two experiments in fertilizing the
palm, Gleditsch states that he made other preliminary ones in the

74 PLANT HYBRIDIZATION BEFORE MENDEL

Royal Botanical Garden, upon a mastic tree {Pistacia lentiscus),
and on a terebinth {Pistacia terebinthus), both of which were suc-
cessful, especially so in the case of the latter, from which he was
able to collect nearly half a "Metze" — nearly two liters — of seed.
After the two experiments mentioned, Gleditsch remarks that
he allowed the palm to remain eighteen years, without securing
another fertilization, not, however, without having taken much
pains to procure pollen from other places. At the end of the
time referred to, he addressed himself to Kolreuter, who was at
the time medical adviser to the Margrave of Bade-Bourlach, and
to whom he refers as :

"One of the most diligent naturalists of our times, who sent me, in the
month of May, some of this powder of the flowers, which I had searched
for since so long in vain, with a little quantity of the same powder which
he had already kept for a year." (p. 9.)

The latter, he states, had no fertilizing effect, but the former
was entirely effective. The details of the experiment are not un-
interesting. The palm put out successively eleven clusters of
flowers between the ninth and twenty-sixth of May. The tree was
thoroughly rid of all debris and of all clusters of dried flowers.
On account of the height of the tree, it was necessary to erect a
scaffold around its crown, so that the flowers could be readily
pollinated, and subsequently be observed as long as necessary. Of
the eleven flower clusters, three were chosen for pollination, which
were the nearest to the glass of the greenhouse and hence the
m.ost exposed to the sun.

One of these, the smallest, was pollinated with the pollen which
had been kept for a year, "but," he says, "it did not produce any
effect, as I was able from the first to observe at the end of fifteen
days." (p. 10.) The second and third clusters were pollinated with
the fresh pollen.

"Having been obliged to keep for eight days the fertilizing powder
which had been sent me from Carlsruhe, I proceeded to the second fe-
cundation, in the manner which I have already related, in the last days
of the month of May." (p. 10.)

"when I afterwards examined," he continues, "what had been the effect
of the powder on the flowers, I found that the edge of the flower with
the blunt anthers had fallen, or at least had suffered some change, the
little ovaries had become softened, had taken on a little growth, their
color had become modified, and they had become brilliant." (p. 11.)

In his first two pollination experiments with this tree, Gleditsch

PLANT HYBRIDIZATION BEFORE MENDEL 75

relates that he had simply sprinkled the pollen over the flowers
without more ado. On this third occasion, he pollinated the pistil-
late flowers with a camel's-hair brush and, as he states, he did not
omit a flower. At the end of the seventh month, the large cluster
fertilized produced ripe and perfect fruits, those of the first
flowers being the largest, the later ones being of different sizes,
by reason of the diminishing amount of light and heat from the
sun. The form gf the fruits is described as resembling olives, and
their color, nut-brown, and in the best specimens, chestnut-brown.
The outer coat of the fruit is described as being fine and very
brilliant, the interior thick, filamentous and grayish. Under this
was the fleshy soft envelope of the seed, which is described as
having the color of fresh mace. The odor of the flesh of the fruits
is described as disagreeable, resembling at maturity the odor of
old butter, whence the name in Germany "Butter-palm." The taste
of the fruits is stated to be sharp, corresponding, in certain re-
spects, to the odor. As the result of his experiment, Gleditsch con-
cludes that :

"The action which is required to produce a rather considerable change
has not taken and does not take place without an actual contact, imme-
diate or mediate, of the two palms, as is required in male and female
animals, conformably with the general laws of nature, and with the
manifest testimony of experience. The contact takes place in fact in
plants, but, so far as we are informed at present, the sole way consists
in the powder of the flowers of the male plant, where, following the
distinct idea which science can furnish us, is found contained that which
serves for the fecundation of the plant." (p. 13.)

It is important to note that at no time does Gleditsch appear to
have had a clear idea as to the manner of the germination of the
pollen grains. The substance in their interior, he says :

"when it is perfected, and when its time for escaping has arrived, does
so little by little, without the vesicles breaking for this effect." (p. 15.)

The character of the contents of the pollen grains is taken to
be of the nature of an oil, since, on macerating a quantity of pine
pollen in a mortar with mercury, he obtained a substance resem-
bling wax, which could be kneaded between the fingers, but which
was not quite wax, he says, for, when placed in an envelope of
paper, it was found that "it penetrates all the paper with its
subtle oil."

This oil is apparently, in Gleditsch's mind, the material agent
of fertilization. The pollen grains fall upon the stigma, which is

76 PLANT HYBRIDIZATION BEFORE MENDEL

covered with fine "warty projections" (vermes deliees), "between
which the powder of the plants is carried externally, and spreads
its oil." (p. 16.) The stigma exudes also a secretion, which
Gleditsch considers to represent the contribution of the pistillate
plant to fecundation, as the "huile" from the pollen grains con-
stitutes the corresponding contribution of the staminate plant.

"These two singular sorts of humidity, which are particularly filtered
in the flowers, and of which one exudes from the powder of the male
flowers, the other from the tube of the ovary, or from the style of the
female flower, unite and mingle together, whereby the one alters the
properties of the other and produces a substance of a third nature, which
participates in those of the two preceding, and which manifests itself
more or less in the young plants, after fecundation and propagation."

(P- 17.)

The actual process of fertilization, by means of this united sub-
stance, is stated by Gleditsch to be as follows :

The most refined of these two fluid substances thus united, is
carried by suction into the ovary, where it enters the newly-
formed and undeveloped seeds, in a short time causing there, by
means of its proper force, a great change in the "pithy center"
(point moelleux) found there, i.e., within the ovules; furnishing
it (the point moelleux) its nourishment, and laying the founda-
tions for the final development of the young plant newly formed
there. It appears, therefore, according to the view here represented
(p. 17), that an undifferentiated central point of some kind is
assumed to exist in the ovules; that an oily fertilizing material,
exuding by degrees from the pollen grains, penetrates to the
ovary, generally by means of "canaliculi" often extremely min-
ute, enters the ovules, and reaches the "pithy center" referred
to as :

"That part of the marrow or pith, which, coming from the plant, has
terminated in the ovary of the flowers."

The fertilizing substance furnishes to this special "marrow"
the addition of a living fluid, which puts it in condition to extend,
and which is at the same time its first aliment, (p. 17.) We have
at the present time, he says, only a confused idea of the process.

"We are not able to venture to judge it, except after the visible result
of expansion and development, of which we have just spoken." (p. 17.)

This concludes the account of one of the most notable confirma-
tory experiments in pollination, conducted expressly for the pur-

PLANT HYBRIDIZATION BEFORE MENDEL 77

pose of verifying the theory of the sexuality of plants, and car-
-ried out with scientific thoroughness and accuracy.

This outlines the history of the more important experiments
known to have been performed in connection with the investiga-
tion of sex in plants, to the days of Kolreuter.

By the middle of the eighteenth century, therefore, little doubt
should have remained in scientific minds regarding the existence
of sex in plants, or as to the necessity of the pollen as a fertiliz-
ing agent. As Kolreuter himself says :

"The pollen is a collection of organic particles, which in every plant
have a definite form ; it is the true instrument in which the male fer-
tilizing material (Saamen) is produced, disengaged, and made suited for
dissemination." ("Vorlaufige Nachricht," p. 7.)

Actual experiments in fertilization, many of them between
plants of different species, had been successfully carried out in
more than twenty important groups of plants, from many differ-
ent families. We have also in Kolreuter's work a careful study
of the characteristics of hybrids, obtained in sixty-five different
hybridization experiments, conducted with species from a dozen
different genera, belonging to diverse families, together with an
accurate comparison of the characters of the hybrid plants of
the first generation with those of their parents.

A scientific foundation had therefore been laid for genetic work
in the breeding of plants. The value of Kolreuter's own experi-
mental work was doubted, however, by influential contemporary
critics, although Sageret (10), whose opinion should have carried
weight, said of it :

"Having several times repeated his experiments, I have occasion to con-
vince myself more and more of his exactitude and of his veracity; I be-
lieve then that he merits all confidence."

Kolreuter began with perfectly settled convictions regarding
sexuality in the plant kingdom. In the preface to his "Vorlaufige
Nachricht" of September 1, 1761, he states that he would have
accompanied his manuscript material with special proof concern-
ing sex in plants, if he had not considered it in his present view
(bey gegenwartiger Absicht) as in the highest degree superfluous.

"The most important of these [e.g., the proofs in question] anyone can
deduce therefrcm, who has only to a tolerable degree a conception of
this subiect. I flatter myself in the meanwhile with the good hope that,
if not through the already propounded propositions alone, yet at least

78 PLANT HYBRIDIZATION BEFORE MENDEL

through the whole of the plan of my observations and experiments, which
will appear in the above-mentioned treatise, and of which the ones here
presented are only a small part, I shall completely convince everyone,
even the most stiff-necked doubter, of the truth of the sex of plants, if,
contrary to all suppositions, such an one should still be found, who, after
a close examination, still maintained the contrary, it would be as greatly
a surprise to me, as though I heard anyone maintain at clear midday that
it is night." ("Vorlaufige Nachricht," Vorrede, p. 5.)

Despite the fact that Kolreuter had demonstrated conclusively
the possibility of crossing plants, even "species," artificially,
and had even laid the foundations for a knowledge of the laws
governing hybrids, much doubt still remained in the minds of
botanists, regarding the facts which Camerarius' and Kolreuter's
experiments demonstrated. As Sachs remarks (9, p. 413) :

"The plant collectors of the Linnaean school, as well as the true
systematists at the end of the eighteenth century, had little understand-
ing for such labors as Kolreuter's, and incorrect ideas on hybrids and
their power of maintaining themselves prevailed in spite of them in
botanical literature."

Gartner says of Kolreuter's work, writing In 1849 (3 c, p. 5) :

"Hybridization in its scientific significance was so little thought of,
and at the most regarded merely as a proof of the sexuality of plants,
that the many important suggestions and actual data which this diligent
and exact observer recorded in various treatises have found but little
acceptance in plant physiological papers up to the most recent time. On
the other hand, even in respect to the sexuality of plants, they were at-
tacked to such a degree that their genuineness was doubted and strenu-
ously contradicted, or else they were regarded as a sort of inoculation
phenomenon belonging to gardening."

11. Christian Konrad Sprengel.

Christian Konrad Sprengel was born in Brandenburg a H. in
1750, as the fifteenth son of a clergyman. He studied theology
and philology at Halle, and in 1774 became instructor in the
school of the King Frederick Hospital, and at the Royal Military
School in Berlin.

After six years of service, he was appointed (1780) to the posi-
tion of Head (Rector) of the large Lutheran city school at Span-
dau, where his teaching was largely in the ancient languages,
a position which he held until 1794. In this year he was retired
on a pension, and spent his remaining years in Berlin, living in
quite simple circumstances, until his death, which occurred April
7, 1816.

At the suggestion of a Dr. Heim, then a practising physician

PLANT HYBRIDIZATION BEFORE MENDEL

in Spandau, and afterwards a celebrated physician in Berlin, he
was led to take up botanical studies as a relief from hypochron-
dria. It was thus that Sprengel became interested in the biology of
the flower, and hence finally, in 1793, published the results of

X>M ^

W« 4

\\\l !

vxy

tMit(l(M'kf<" (M^luMuniils

Plate XXIII. Title-page of Sprengel's "Das entdeckte Geheimniss der Natur."

8o PLANT HYBRIDIZATION BEFORE MENDEL

five years of minute and extensive observations and studies, in
a folio volume with twenty-five plates, which contained hundreds
of detailed and accurate illustrations of flowers and their parts.
This famous work, "Das entdeckte Geheimniss der Natur im Bau
und in der Befruchtung der Blumen," was based upon the thor-
oughgoing observation and investigation of nearly live hundred
species.

Through lack of funds Sprengel was prevented from publish-
ing the second part of his work, which led him, toward the end
of his life, to give up botany altogether, and devote himself to
classical studies. During his years of retirement in Berlin, he gave
lessons in the classics and in botany for recreation, and on Sun-
days conducted botanical excursions in the neighborhood of Berlin
for small fees.

On account of the dry and formal character of the botanical
science of his time, Sprengel's work remained unnoticed for forty-
three years after his death.

The first serious mention of it in scientific literature appears
to have been that made by Darwin, in the "Origin of Species" in
1859. (6th ed. 1895, p. 119.)

Sprengel is described as a man averse to the conventional flat-
teries of life, and of a rather recklessly open type of character.
In his Berlin excursions he is described as awakening attention
through the wealth of his knowledge and his inwardly spiritual
character, and as arousing interest alike in all the objects of
nature, — an inscription on a gravestone, the construction of a
windmill, the course of the stars, and the body of a plant. Dur-
ing Sprengel's Spandau period, it is stated, a large portion of his
thirteen years of official duty was filled with an almost unbroken
chain of events involving insubordination, quarrels with the au-
thorities, and friction with the parents of the pupils, which cir-
cumstances led him to be described by a local chronicler as "in-
human in his punishments, arbitrary in his teaching, stubborn, and
little religious." The whole truth appears to have been that Spren-
gel was a man of a large and powerful nature, with considerable
intellectual gifts, rich knowledge, and aware of his own state of
advancement, but uncompromising, and, from having been forced
into too confined and narrow an environment in which his ideas
and prepossessions found little opportunity for expression, his na-

PLANT HYBRIDIZATION BEFORE MENDEL 81

ture consequently spent itself in intractable and dictatorial con-
tentions.

Of his botanical knowledge, gained during his Spandau studies,
his contemporary, Willdenow, afterward the first professor of
botany in the University of Berlin, made use in his "Prodromus
Florae Berolinensis," 1787, and praised the self-taught botanist
as "a thoroughly keen-minded plant investigator."

The discoveries of Christian Konrad Sprengel should have
called attention to Kolreuter's antecedent discovery of the relation
between insects and flowers. While Camerarius had demonstrated
the fact that plants possess sex, and Kolreuter had shown that
fertile hybrids could be produced between plants of different
kinds, the further fact, that crossing in nature, at least among
different individuals of the same species, is a common and ordi-
nary phenomenon in the plant kingdom, was not at all known.
Aware, as we are today, that the improvement of cultivated plants,
due to the appearance of new strains and varieties, is to be ac-
credited largely at the outset to the natural crossing of individuals
standing in fairly close genetic relationship to one another, we
can see the great importance, in the history of plant breeding, of
Sprengel's discovery that flowers are commonly pollinated by
insects, and that there is an intimate interrelationship between the
plant and the insect worlds,

Sprengel's epoch-making book "The Newly-revealed Secret of
Nature in the Structure and Fertilization of Flowers" fii) con-
stitutes a third great landmark in plant breeding, after the orig-
inal discovery of the possibility of artificial pollination by the
Mesopotamian date growers. Such a wealth of accurate first-hand
observations on the adaptations of flowers to cross-pollination
had never before been made. To Sprengel also is due the discov-
ery of dichogamy, i,e., the maturing of the stamens and the pis-
tils of flowers at different times. His conclusion, that nature in
most cases intended that flowers should not be fertilized by their
own pollen, and that the peculiarities of flower structure can only
be understood when studied in relation to the insect, was revolu-
tionary for his time.

Sprengel's work has been well described by Sachs, as "the first
attempt to explain the origin of organic forms from definite rela-
tion to their environment." (9, p. 415-)

82 PLANT HYBRIDIZATION BEFORE MENDEL

Conceding the fact that plants actually have sex, it is plain
that some kind of breeding must be possible. Granting that hy-
brids even between different species can be produced, it is fur-
ther plain that new kinds of plants can be originated. But what
of the additional fact, the contribution of Sprengel, that in gen-
eral nearly all flowering plants with definite floral envelopes are
naturally cross-fertilized. It signified that the bringing together
of combinations of parental characters is the rule rather than the
exception in nature, and that, therefore, the breeding of new types
in the plant world may be said to be going on all the time. It
remained for Darwin to show how the results from such perpetual
crossings are limited and held in check by the operation of natural
selection. At all events, Sprengel's discoveries at once disclosed at
least an important reason for diversity, for so many variations in
nature, upon which fact man had unconsciously depended for the
selection of "superior" types of plants, and hence for the "im-
provement" of races.

Unfortunately, the discoveries and disclosures of Sprengel
awakened little interest at the time. Like the work of Camerarius
and Kolreuter, the investigations of Sprengel, in turn, suffered
comparative obscurity. Biologists of his day believed in the dogma
of the fixity of species, upon which Kolreuter's and Sprengel's
experiments and discoveries regarding cross-pollination by means
of insects tended to cast doubt, and to require the substitution,
for the doctrine of the fixity of species, of the principle of the
comparative stability of organic forms.

Although the scientific world traces a continuity of thought
and investigation from Gartner back to Camerarius, the fact must
not be lost sight of that each of the three chief investigators who
laid the early foundations of plant genetics, Camerarius, Kolreu-
ter, and Sprengel, was considerably ignored by the biological sci-
ence of his own time.

Two generations elapsed from the time of Camerarius to that
of Kolreuter, and another from Kolreuter's time to that of Spren-
gel. It is more than a fourth generation from Sprengel's publica-
tion to the time of the work of William Herbert (1837) ; a third
of a generation more to the appearance of Gartner's memoir
(1849), and about half of another generation again, before the
appearance of Mendel's celebrated papers (186:6^, and finally,

PLANT HYBRIDIZATION BEFORE MENDEL 83

more than another generation until the date of the rediscovery
of Mendel's work (1900), the beginning of the scientific period
properly speaking.

BIBLIOGRAPHY

1. Bradley^ Richard.

New Improvements of Planting and Gardening, both Philo-
sophical and Practical, explaining the motion of Sap and
Generation of Plants. 6th ed. London, 1718,

2. Focke, Wilhelm Olbers.

Die Pflanzenmischlinge, ein Beitrag sur Biologie der Ge-
wachse. Berlin, 1861.

3. Gartner^ Carl Friedrich von.

(a) Over de Voortling van Bastard-Planten, Eene Bijtrage
tot de Kenntniss van de Bevruchting der Gewassen.
Haarlem, 1838.

(b) Versucheund Beobachtungeniiberdie Befruchtungs-organe
der volkommeneren Gewachse, und iiber die natiirliche
und kiinstliche Befruchtung durch den eigenen Pollen.
Stuttgart, 1844. •

(c) Versuche und Beobachtungen iiber die Bastarderzeugung
im Pflanzenreich, mit Hinweisung auf die ahnlichen
Erscheinungen im Thierreiche. Stuttgart, 1849.

(d) Methode der kiinstlichen Bastardebefruchtung der Ge-
wachse, und Namensverzeichniss der Pflanzen mit wel-
chen Versuche angestellt wurden.

4. Gleditsch^ Johann Gottlieb.

Essai d'une fecondation artificielle, fait sur I'espece de pal-
mier qu'on nomme Palma dactylifera folio flabelliformi. His-
toire de I'Academie royale des Sciences et de Belles Lettres
de Berlin, 1749, pp. 103-8.

5. Grew, Nehemiah (1641-1712).

(a) The anatomy of vegetables begun, with a general ac-
count of vegetation grounded thereon, June 11, 1672.

(b) The anatomy of plants. 1682.

84 PLANT HYBRIDIZATION BEFORE MENDEL

6. Logan^ James.

(a) Experimenta et naeletemata de plantarum generatione.
Lugduni Batavorum (Leiden), 1739.

(b) Experiments and considerations on the generation of
plants. 2nd edition of the above, English and Latin on
opposite pages, and with both English and Latin title
page. London, 1747.

7. Miller, Philip.

Gardeners' Dictionary, containing the best and newest meth-
ods of cultivating and improving the kitchen, fruit flower-
garden, and nursery, etc. 7th ed. London, 1759.

8. Moreland, Samuel.

Some observations upon the parts and uses of the flower in
plants. Phil. Trans. Roy. Soc. 23: 1474-79. 1702-03.

9. Sacks, Julius von.

History of Botany, 1530-1860. Translated by Garnsey and
Balfour. 2nd impression, Oxford, 1906.

10. Sageret, Augustin.

Considerations sur la production des hybrides, des variantes,
et des varietes en general, et sur celles des Cucurbitacees en
particulier. xA.nnales des Sciences Naturelles, 18:294. 1826.

1 1 . Sprengel, Christian Konrad.

Das entdeckte Geheimniss der Natur im Bau und in der Be-
fruchtung der Blumen. (1793), ed. Paul Knuth. In Ost-
wald's Klassiker der exakten Wissenschaften, No. 48, 4 vols.
Leipzig, 1894.

CHAPTER IV

THE EARLY ENGLISH HYBRIDISTS

AT the beginning of the nineteenth century there began to
appear in England the first signs of the application of the
science of hybridization to the practical art of breeding, in
the work of Thomas Andrew Knight, and of William Herbert.

12. Thomas Andrew Knight.

Thomas Andrew Knight was a country gentleman by occupa-
tion. Born August 12, 1759, he was educated at Oxford, and early
began to interest himself on his estate at Elton in Herefordshire
in experiments in the raising of new varieties of fruits and vege-
tables. In 1795, his work as a horticulturist first became known
through some papers read at the sessions of the Royal Society.
He was an organizer of the Horticultural Society of London,
founded 1804, of which he was president from 1811 until his
death in 1838. He was an annual contributor to its "Transac-
tions," and was the author of upwards of one hundred papers.
In 1841, three years after his death, a collection of eighty-two
of his papers was published by the botanists Bentham and Lind-
ley. Of Knight's published papers, forty-six are enumerated in
the Royal Society's Catalogue. Knight was not a scientific man,
but a practical horticulturist with scientific instincts, who pro-
ceeded on the principle that the improvement of plants depended
upon the same scientific laws as the improvement of animals, and
that cross-breeding was the key to the origination of new and im-
proved sorts. His principal work of crossing was carried out with
currants, grapes, apples, pears, and peaches, to the end of pro-
ducing hardier and superior fruits. One of his discoveries of
genetic interest was that in crosses of varieties of red upon white
currant, by far the greater number of the hybrids produced red
fruit, in other words demonstrating the dominance of red. A con-

I
f

Plate XXIV. Thomas Andrew Knight, 1759-1838.

PLANT HYBRIDIZATION BEFORE MENDEL 87

elusion formulated by Knight, on the basis of his experience,
afterwards confirmed by Darwin, and since called the Knight-
Darwin law, was that:

"New varieties of every species of fruit will generally be better- ob-
tained by introducing the farina (pollen) of one variety of fruit into the
blossom of another, than by propagating from one single kind." (3f,
p. 38.)

However, the work of Knight which attracts the most atten-
tion from the standpoint of genetics is his experiment with peas.
The paper in question, read before the Horticultural Society, June
3, 1823, was entitled "Some Remarks on the Supposed Influences
of the Pollen, in Cross-breeding, on the Color of the Seed-coats
of Plants and the qualities of Their Fruits."

This paper is really, in part, a reply to certain phases of the
experiments of John Goss upon the same plant. Knight's intro-
ductory statement, which follows, is a curious reminder in point
of form of Mendel's own introduction to his report upon his ex-
periments with peas nearly half a century later. Knight says :

"The numerous varieties of strictly permanent habits of the pea, its
annual life, and the distinct character in form, size and color to many
of its varieties, induced me, many years ago, to select it for the purpose
of ascertaining, by a long course of experiments, the effects of introduc-
ing the pollen of one variety into the prepared blossoms of another.
My chief object in these experiments was to obtain such information as
would enable me to calculate the probable effects of similar operations
upon gther species of plants, and I believe it would not be easy to sug-
gest an experiment of cross-breeding upon this plant, of which I have
not seen the result, through many successive generations." (sf, p. 378.)

In the particular experiment in question Knight determined
that, in crossing a pea with grey seed-coats upon one with white
seed-coats, no immediate change in color took place, but that the
resulting hybrid seeds produced plants the next year which uni-
formly bore grey seeds, as well as having the purple-colored
stems and the flowers of the male parent. He further discovered
the fact that by crossing plants grown from these (heterozygous)
grey seeds, with pollen from what he calls a "permanent" white
variety, plants of two types appeared, one bearing grey and the
other white seeds — in other words, in modern terms, the result
of the cross of a recessive white upon a hybrid dominant grey.
No numbers are reported, so that a scientific basis of ratios, as
later found by Mendel, was not laid.

88 PLANT HYBRIDIZATION BEFORE MENDEL

Twenty-five years earlier, in 1799, Knight undertook experi-
ments with plants to test the theory of "superfoetation," that is
to say, the possibility of two males combining in the fecundation
of a female. At the time, the behavior of the fertilizing cells was
absolutely unknown, as was the fact that but one sperm cell was
required to fertilize the egg. In fact, cells as such, and their func-
tion, were not as yet discovered. It was quite commonly supposed,
for instance, that an excess of pollen in pollination produced an
excess effect amounting to a preponderating evidence of the male
characters in the offspring.

Peas were chosen for the purpose of the experiment in ques-
tion. The principal object was to obtain new and improved vari-
eties of apples, but inasmuch as years must elapse before the
results would become known, it was resolved, in the interval, to
experiment with annual plants.

"Among these," he says, "none appeared so well adapted to answer
my purpose as the common pea ; not only because I could obtain many
varieties of this plant, of different forms, sizes and colors ; but also be-
cause the structure of its blossoms, by preventing the ingress of insects
and adventitious fauna, has rendered its varieties remarkably perma-
nent." (3a, p. 196.)

Having a variety in his garden which appeared to him, from
having been long grown in the same soil, to have lost its vigor,
he emasculated a dozen flowers upon it in 1787, pollinating half
of them with the pollen from "a large and luxuriant grey pea,"
leaving the other half dozen as they were. The ovules in the
pods of the unfertilized flowers, withered, of course.

"Those in the other pods attained maturity, but were not in any sen-
sible degree different from those afforded by other plants of the same
variety, owing, I imagine, to the external covering of the seed (as I have
found in other plants) being furnished entirely by the female." {ib.,
p. 197.)

Knight was thus induced to take up garden peas for his ex-
periments, for the same reason, as stated, that led Mendel later
to do likewise. His reflections upon the reason for the act of fer-
tilization by pollen from the grey-seeded pea (i.e., with grey seed-
coats) not affecting the fertilized ovules in respect to their seed-
coats, show the mind of an acute observer.

"in the succeeding spring the difference, however, became extremely
obvious ; for the plants from them rose with excessive luxuriance, and
the color of their leaves and stems clearly indicated that they had all

PLANT HYBRIDIZATION BEFORE MENDEL 89

exchanged their whiteness for the color of the male parent; the seeds
produced in autumn were dark gray." {ib., p. 197.)

Here, then, is the first recorded instance of color-dominance in
peas. Knight, however, did not follow out the results to the next
generation from the selfed hybrids, but re-pollinated the hybrids
with pollen from a white variety, as the result of which, he says,
there were produced a variety of new kinds,

"Many of which were, in size and in every respect, much superior to
the original white kind, and grew with excessive luxuriance, some of them
attaining the height of more than twelve feet. I had frequent occasion
to observe, in this plant, a stronger tendency to produce purple blossoms
and colored seeds than white ones ; for, when I introduced the farina of
a purple blossom into a white one, the whole of the seeds in the succeed-
ing year became colored." {ib., p. 197.)

Here again is an early observation of the fact of dominance,
and possibly of heterosis. Knight proceeds to the conclusion that,
by mixing the pollen of the two kinds of peas, he could, through
the behavior of the seeds, readily determine whether "superfoeta-
tion" had taken place or not. In view of the non-existence of
"superfoetation," except in the rare cases of dispermy, the experi-
ment itself is not of importance, but it brought forth the follow-
ing remark, which is interesting as showing Knight's knowledge
of the fact of dominance of grey seed-coat color.

"For as the offspring of a white pea is always white, unless the farina
of a colored kind be introduced into the blossom, and as the color of the
gray one is always transferred to its offspring, although the female be
white, it readily occurred to me, that if the farina of both were mingled
or applied at the same moment, the offspring of each could be easily
distinguished." {ib., p. 198.)

Pollinating the flowers of some of the hybrids with the pollen
from a white-seeded pea, he says, "The second year I obtained
white seeds." Here, he should have obtained gray and white, half
and half, but he makes no mention of numbers, since the numeri-
cal relations of the seeds did not occur to him as being significant.

It is interesting to note the results of Knight's experiment in
reciprocal crossing.

"By introducing the farina of the largest and most luxuriant kinds
into the blossoms of the most diminutive, and by reversing this process,
I found that the powers of the male and female, in their effects upon
the offspring, are exactly equal." {ib., p. 200.)

The vigor of growth, the size of the seeds procured, and the

90 PLANT HYBRIDIZATION BEFORE MENDEL

season of maturity were the same, although the one was a very
early and the other a very late variety.

"I had in this experiment, a striking instance of the stimulative effects
of crossing the breeds ; for the smallest variety, whose height rarely ex-
ceeded two feet, was increased to six feet, whilst the height of the large
and luxuriant kind was very little diminished." {ib., p. 2CK).)

Despite the fact that Focke says (Pflanzenmischlinge, p. 436)
"he has contributed more to our knowledge of hybrids than any
other writer during the first half of the nineteenth century" — a
statement which may, of course, perhaps be seriously disputed —
it is nevertheless true that Knight was the first experimenter to
apply the science of plant hybridization to plant improvement.
Although endowed with scientific insight of no mean order, his
chief claim to recognition as a plant breeder lies in the fact that
he possessed a practical instinct for getting improved orchard
fruits into existence. Knight remarked upon the fact that it had
long since been ascertained by physiologists that, since the seed-
coats, or membranes which cover the cotyledons of the seed, to-
gether with the receptacles which contain them, are visible for
some time before the blossoms reach their full growth, therefore
the existence of such structures is independent of the influence
of the pollen. The fact is also that the seed-coats and the fruit
of some species reach nearly if not completely their full growth,
when the pollen has been entirely withheld ; therefore, from these
and other observations, he concludes:

"it has been inferred that neither the external cover of the seeds, nor
the form, taste or flavor of fruits, are affected by the influence of the
pollen of a plant of a different variety or species." (3f, p. 377.)

There exists, however, he continues, some diflFerence of opinion
in this regard, the experiments of Goss appearing to support the
opinion that :

"The color of the seed-coat, at least, may be changed by the influence
of the pollen of a variety of different character." {ib., p. 378.)

The account which Knight then gives of his experiments is as
follows :

When the pollen of a grey-seeded pea was used to fertilize the flowers
of a white variety, "no change whatever took place in the form, or color,
or size of the seed ; all were white, and externally quite similar to others
which had been produced by the unmutilated blossoms of the same plant."
{lb., p. 379-)

PLANT HYBRIDIZATION BEFORE MENDEL 91

These seeds, however, sown the following year,

"uniformly afforded plants with colored leaves and stems, and purple
flowers ; and these produced gray peas only." {ib., p. 379.)

In the case of Goss's "Blue Prussian" Pea, Knight continues,
the cotyledons being blue in color, and this color being percepti-
ble through the semi-transparent seed-coats, caused the latter to
appear blue, although they were really white. He concludes :

"The color of the cotyledons only was, I therefore conceive, changed,
whilst the seed-coats retained their primary degree of whiteness." {ib.,
P- 379.)

Knight therefore finally holds that the opinions that neither
the color of the seed-coats, nor the form, taste, or flavor of
fruits, are ever affected by the immediate influence of the pollen
of a plant of another variety or species, are well-founded {ib.^
p. 380.)

Knight thus built up an opinion of a general character regarding
the fruits of plants, based upon his experiments involving the seed-
coats alone. However insufficient such a conclusion seems at the
present time, drawn from such partial premises, it is explainable
by the fact that the morphology of seed-development was, at
that time, little understood, so that the factors affecting any one
part of the fruit, such as the seed-coats, might easily be conceived
of as similarly affecting other parts.

The following examples will serve to illustrate the nature of
his results. Of his currant crosses, he says :

"Five varieties, three red* and two white, out of about two hundred,
appeared to me to possess considerably greater merits than either of
their parents, and one of the red will, I believe, prove larger than any
red currant now in cultivation."

By crossing the "Noblesse" peach (female) by "Nutmeg"
(male), he obtained about twenty seedlings, of which three:

"Appeared better peaches than I previously possessed." Of one of these
he says : "its fruit has attained a more uniform degree of perfection than
I have ever witnessed in any other variety. The trees have also been free
from every vestige of mildew, in a situation where the disease is very
prevalent, and have entirely escaped the attacks of insects."

In 1809, Knight gave a paper before the Royal Society, en-
titled : "On the comparative influence of male and female par-
ents on their offspring." (3c.)

Prompted by the conception of Linnaeus, "that the character

92 PLANT HYBRIDIZATION BEFORE MENDEL

of the male parent predominated in the exterior parts of both
plants and animals," Knight undertook some experiments with
the different species of fruit trees, but most extensively with the
apple. He makes the general statement:

"I have observed that seedling plants, when propagated from male and
female parents of distinct characters and permanent habits, generally,
though with some few exceptions, mherit much more of the character of
the female, than of the male parent." (p. 393.)

Without commenting upon this generalization, the experiments
themselves may be briefly noticed. Crosses were made between
the British and the Siberian crab-apple, which as, he says,

". . . however dissimilar in habit and character, appear to constitute a
single species only, in which much variation has been effected by the in-
fluence of climate on successive generations." (p. 395.)

Knight reports a reciprocal cross between apple and Siberian
crab. Both trees were trained to walls, where they blossomed
earlier than ordinarily. All the flowers on the two trees except
those used were removed and the stamens carefully removed from
the remaining ones. Of the plants produced by cross-pollination.
Knight says :

"There was a very considerable degree of dissimilarity in the appear-
ance of the offspring; and the leaves, and general habits of each, pre-
sented an obvious prevalence of the character of the female parent."

(P- 393-)

Where the British crab-apple was used as the female parent,

the buds did not unfold quite so early in the spring, and their

fruits generally exceeded very considerably in size those which

were produced by the trees which derived their existence from

the seeds of the Siberian crab.

"There was also a prevalence of the character of the female parent
in the form of the fruit." (3c, p. 394.)

The greater portion of the article is taken up with a discussion
of similar cases in animal breeding. One observation is not with-
out interest.

"In several species of domesticated or cultivated animals (I believe in
all), particular females are found to produce a very large majority, and
sometimes all their offspring, of the same sex; and I have proved re-
peatedly that, by dividing a herd of thirty cows into three equal parts,
I could calculate, with confidence, upon a large majority of females from
one part, of males from another, and upon nearly an equal number of
males and females from the remainder. I have frequently endeavored to

PLANT HYBRIDIZATION BEFORE MENDEL 93

change these habits by changing the male ; but always without success,
and I have, in some instances, observed the offspring of the one sex,
though obtained from different males, to exceed those of the other in
the proportion of five or six and even seven to one. When on the con-
trary, I have attended to the numerous offspring of a single bull, or ram,
or horse, I have never seen any considerable difference in the number of
offspring of either sex." (3c, pp. 397-8.)

This interesting empirical observation is quoted as being of his-
torical interest, and the observation regarding the difference in
the reciprocal apple crosses is worth preservation.

Knight sums up his practical views upon the relation of the
science of botany to the breeding of plants in the following
words :

"I cannot dismiss the subject, without expressing my regret, that those
who have made the science of botany their study, should have considered
the improvement of those vegetables which, in their cultivated state, af-
ford the largest portion of subsistence to mankind, and other animals,
as little connected with the subject of their pursuit. Hence it has hap-
pened that whilst much attention has been paid to the improvement of
every species of useful animals, the most valuable esculent plants have
been almost wholly neglected. But when the extent of the benefit which
would arise to the plants, which, with the same extent of soil and labor,
would afford even a small increase of produce, is considered, this subject
appears of no inconsiderable importance. . . . The improvement of ani-
mals is attained with much expense, and the improved kinds necessarily
extend themselves slowly; but a single bushel of improved wheat or peas
may in ten years be made to afford seed enough to supply the whole
island." (3a, p. 204.)

Focke, in his Pflanzenmischlinge," pp. 432-3, gives the follow-
ing summary of Knight's services to the science and practice of
hybridization :

"Toward the end of the eighteenth century, a man appeared, whose
works have been of particular significance for the knowledge of fertiliza-
tion and crossing, Thomas Andrew Knight, the celebrated fruit and vege-
table breeder. Starting with the successful efforts of the animal breeders,
he came upon the thought whether it was not possible to improve do-
mestic animals through crossing the races, to obtain more admirable sorts
of economic plants. Without knowing anything of Kolreuter, he began
his experiments with fruit trees, and from 1787 on, with peas, with which
he was naturally able much earlier to turn out definite results. The pro-
geny of his crossed races of peas gained extraordinarily in vigor and yield.
Already in 1799 ('Phil. Trans.,' 1799, Part I, p. 202), Knight was able to
express the principle, that nature intended that a sexual intercourse
should take place between neighboring plants of the same species. He
laid down this principle through his results in individual and race crosses,
especially in the genus Pisum."

94 PLANT HYBRIDIZATION BEFORE MENDEL

13. Wtllimn Herbert.

The work of William Herbert was to a considerable extent con-
temporary with that of Knight. Born January 12, 1778, son of the
Earl of Carnarvon, educated at Eton and Oxford, he was trained
for the bar, which he finally left for the Church, entering orders,
and finally becoming Dean of Manchester. Fond of out-door life
and sport, he possessed also, in addition to literary talent, an
instinct for plant studies. Herbert worked largely on the im-
provement of florists' flowers but also conducted experiments with
some agricultural plants. He was engaged for a considerable time
upon his own experiments, before he came upon the work of
Kolreuter, some fifty or more years before his day, which he im-
mediately assimilated, and estimated at its true value, as the
following comment indicates :

"The first experiments, with a view to ascertain the possibility of pro-
ducing hybrid vegetables, appear to have been made in Germany, by
Kolreuter, who published reports of his proceedings in the Acts of the
Petersburgh Academy between fifty and sixty years ago. Lycium, Digi-
talis, Nicotiana, Datura and Lobelia were the chief plants with which he
worked successfully, and as I have found nothing in his reports to the
best of my recollection opposed to my OAvn general observations, it is
unnecessary to state more concerning his mules than the tact that he was
the father of such experiments. They do not seem to have been at all fol-
lowed up by others, or to have attracted the attention of cultivators or
botanists as they ought to have done ; and nothing else material on the
subject has fallen under my notice of earlier date than Mr. Knight's re-
port of his crosses of fruit trees, and my own of ornamental flowers, in
the Transactions of the Horticultural Society of London. Those papers
attracted the public notice, and appear to have excited many persons,
both in this country and abroad, to similar experiments." (2c, p. 335.)

In the year 1819, after having paid attention for some years

to the production of hybrid plants, but then unaware of the work

of Kolreuter, Herbert brought his views on the subject of hybrids

before the Horticultural Society, and they were published in the

"Transactions" of that body. He comments upon the matter as

follows:

"It is, however, satisfactory to find at the present day, after the atten-
tion of botanists and cultivators has been fully called to the subject
during the space of many years, and a multitude of experiments carried
on by a variety of persons, that, although our knowledge of its mysteries
is still very limited, my general views have been fully verified, and my
anticipations confirmed in a manner which I was scarcely sanguine enough
to have expected." (2c, p. 336.)

The view then quite generally prevalent among botanists con-

PLANT HYBRIDIZATION BEFORE MENDEL 95

cerning hybridization was that a fertile cross was of itself proof
that the two parents were of the same species, while sterile off-
spring constituted conclusive evidence that they were of different
species. This view was held, as Herbert says :

"without suggesting any alteration in the definition of the term
'species,' but leaving it to imply what it had before universally signified
in the language of botanists."

Again he says :

"Having, in fact, the same fundamental opinion, that the production
of a fertile intermixture designated the common origin of the parents, I
held also, what experience has in a great measure confirmed, that the
production of any intermixture amongst vegetables, whether fertile or
not, gave reason to suspect that the parents were descended from one
common stock, and showed that they were referable to one genus ; but
that there was no substantial and natural difference between what bota-
nists had called species, and what they had termed varieties, the distinc-
tion being merely in degree, and not absolute ; so that, without first re-
forming the terms used in botany, and ascertaining more precisely what
was meant by a species, those who argued on the subject were fighting
the air." (2c, p. 337.)

Herbert's entire freedom from any slavish adhesion to the
species idea with respect to hybrids is plainly stated.

"Further experiments have shown," he says, "that the sterility or fer-
tility of the offspring does not depend upon original diversity of stock;
and that, if two species are to be united in a scientific arrangement on
account of a fertile issue, the botanist must give up his specific distinc-
tions generally, and entrench himself within the general." (2c, p. 337.)

"In fact there is no real or natural line of difference between species
and permanent or descendible variety, as the terms have been applied
by all botanists ; nor do there exist any features on which reliance can
be placed to pronounce whether two plants are distinguishable as species
or varieties. Any person, who attends to the subject, will perceive that
no botanist has laid down any precise rules by which that point of in-
quiry can be solved, and that the most variable, contradictory and un-
substantial features have been taken by different persons, and by the
same person on different occasions, to uphold the distinctions they pro-
posed to establish ; the truth being that such distinctions are quite arbi-
trary, and that, if two plants are found capable of inter-breeding, when
approached by the hand of man, they are as much one as if they were
made to intermix more readily and frequently by the mere agency of the
wind, or assiduity of insects, and are nT)t separable with more truth by
any positive difference, than the varieties which cannot be prevented
from crossing with each other when in the same vicinity." (2g, p. 341.)

It was the view of Herbert that fertility in hybrids depended
much upon circumstances of climate, soil and situation. He finally
concludes that experiments had made it almost certain

"that the fertility of the hybrid or mixed offspring depends more upon

96 PLANT HYBRIDIZATION BEFORE MENDEL

the constitutional than the closer botanical affinities of the parents."
(2C, p. 342.)

As to whether there was a real fundamental difference between
plants which could produce fertile and those which could produce
only sterile offspring by crossing, Herbert says further:

"it was my opinion that fertility depended much upon circumstances of
climate, soil and situation, and that there did not exist any decided line
of absolute sterility in hybrid vegetables, though from reasons which I
did not pretend to be able to develop, but undoubtedly depending upon
certain affinities either of structure or constitution, there was a greater
disposition to fertility in some than in others. Subsequent experiments
have confirmed this view to such a degree as to make it almost certain —
that the fertility of the hybrid or mixed offspring depends more upon
the constitutional than the closer botanical affinities of the parents."
(2c, p. 342.)

He holds that it obtains as a general fact throughout the plant
kingdom, that species which have close botanical affinity, if they
have widely different soil or climatic requirements, are apt to pro-
duce sterile offspring as the result of a cross, while, if they have
the same constitutional habit, they tend to give rise to fertile
offspring.

From the standpoint, then, of a practical plant hybridizer and
horticulturist, Herbert holds that :

"Any discrimination between species and permanent varieties of plants
is artificial, capricious, and insignificant ; that the question which is
perpetually agitated, whether such a wild plant is a new species, or a
variety of a known species, is waste of intellect on a point which is
capable of no precise definition." (2c, p. 346.)

"The effect, therefore, of the system of crossing, as pursued by the
cultivator, instead of confusing the labors of the botanist, will be to
force him to study the truth, and take care that his arrangement and
subdivisions are conformable to the secret laws of nature ; and will only
confound him when his views shall appear to have been superficial and
inaccurate ; while on the other hand it will furnish him an irrefragable
confirmation when they are based upon reality." (2C, p. 346.)

The attitude of Herbert with regard to the production of hy-
brids was not, however, so much the attitude of the scientist as
that of the horticulturist and florist. His point of view is well
stated in the following:

"To the cultivators of ornamental plants, the facility of raising hybrid
varieties affords an endless source of interest and amusement. He sees in
the several species of each genus that he possesses, the materials with
which he must work, and he considers in what manner he can blend them
to the best advantage, looking to the several gifts in which each excels,
whether of hardiness to endure our seasons, or brilliancy in its colors,

PLANT HYBRIDIZATION BEFORE MENDEL 97

of delicacy in its markings, of fragrance, or stature, or profusion of
blossom, and he may anticipate with tolerable accuracy the probable as-
pect of the intermediate plant which he is permitted to create ; for that
term may be figuratively applied to the introduction into the world of a
natural form which has probably never before existed in it." (2c, p. 346.)

With regard to the matter of inheritance of winter-hardiness,
Herbert did some experimentation, as the result of which he found
that the hybrid offspring held an intermediate position, being :

". . . less hardy than the one of its parents which bears the greatest
exposure, and not so delicate as the other; but if one of the parents is
quite hardy and the other not quite able to support our winters, the
probability is that the offspring will support them, though it may suffer
from a very unusual depression of the thermometer or excess of moisture
which would not destroy its hardier parent." (2c, p. 347.)

Regarding the matter of acclimatization, he held substantially

the same view which generally obtains among plant physiologists

of the present day, that:

"it does not appear that in reality any plant becomes acclimated under
our observation, except by crossing with a hardier variety, or by the acci-
dental alteration of constitution in some particular seedling; nor that
any period of time does in fact work an alteration in the constitution
of an individual plant, so as to make it endure a climate which it was
originally unable to bear." (2c, p. 347.)

Entering into details regarding hybrids of his acquaintance,
Herbert notes in fact that the first hybrid among liliaceous plants
appearing in English gardens was the cross between Hippeastrum
vittatum and H. regium. The next being the cross between Crinum
capense, and Crinum zeylanicum in the greenhouse of the Earl of
Carnarvon in 1813.

"It is to be observed," he remarks, "that in some cases, the seminal
varieties of plants preserve themselves almost as distinct in their gen-
erations as if they were separate species" (2c, p. 366),

and instances the cases of the orange, yellow, white, black, red,
and pink hollyhocks, which come true from the seeds, although
planted adjacent in the garden. He speaks also of the tendency
among carnation seedlings to follow-the color of the parent plant.

"j have had greater success," he says, "than any other person in rais-
ing from seed double camellias of various tirtts and appearance, and
some of the best have been produced either from single flowers, or plants
raised from single ones, impregnated by the pollen of double flowers,
preferring, where it can be got, the pollen that is borne on a petal."
(2c, p. 367.)

He notices the curious fact that the striped sorts of camellias

98 PLANT HYBRIDIZATION BEFORE MENDEL

have usually more white in their flowers when they flower early
in the spring, and that the earliest ripening seed of the year is
most apt to yield white or particolored seedlings.

Herbert carried on some experiments with double flowers and,
in 1834, undertook an experiment in the improvement of agricul-
tural plants, pollinating the Swedish turnip (rutabaga) with
pollen of the white, and flowers on another branch of the same
plant with pollen of the red-rooted turnip, which he speaks of as
producing

". . . perhaps a greater tonnage than the white, bearing both frosts
and unfavorable summers better, and thriving in soils where the white
does not succeed." (2c, p. 370.)

The seeds sown, produced good roots the same season :

"The leaves differed in appearance from those of the Swedes, and did
not, like them, retain the rain-water on their surface." (2c, p. 370.)

In the following spring, the hybrids came into flower, the flow-
ers of the hybrids being, for the most part, bright yellow like
those of the male, a smaller number bearing straw-colored flow-
ers like the Swedish turnip, but there were no intermediates.

In a paper entitled "On hybridization amongst vegetables,"
Jour. Hort. Soc. of London, 2:1-28; 81-107 (1847), Herbert dis-
cusses quite at length the species question, and shows how firm
the allegiance still remained to the conception that fertile off-
spring produced from a cross, constituted prima facie evidence
that the parents were within the same species. He says :

"And that is the use of hybridizing experiments, which I have in-
variably suggested ; for, if I can produce a fertile offspring between two
plants that botanists have reckoned fundamentally distinct, I consider
that I have shown them to be one kind ; and indeed I am inclined to
think that, if a well-formed and healthy offspring proceeds at all from
their union, it would be rash to hold them of distinct origin." (2d, p. 7.)

Herbert states {ib., p. 8), that he had had :

". . . no opportunities, by the help of a powerful microscope, of pur-
suing any investigation into the process by which the pollen fertilizes
the ovules,"

and goes on to say that, although he could not therefore under-
take to contradict those who asserted that the pollen grains,

"from their own bulk, emitted tubes which reached from the surface of
the stigma to ovules in the germen" — a distance, as in certain species of
Hymenocallis, amounting to sometimes 12-13 inches — it did not appear

PLANT HYBRIDIZATION BEFORE MENDEL 99

possible to him that "such a minute body should emit a tube of such
length, through which its contents were passed into the ovary, as as-
serted." (p. 8.)

Later on (p. 8) he alludes to the matter again :

". . . it is utterly impossible that such a minute body should emit
such a pipe and its contents, that is, emit it of its own substance," and
adds that he apprehends the truth to be "that by contact with the juices
of the cognate plant it acquires that which enables it to gain bulk for
such an elongation."

Herbert noticed the fact that in species crosses (e.g., Passiflora
coerulea X ony china) the ovaries may develop as the result of the
fertilization stimulus (in this case forming "two fine plump
fruits, two inches long"), the interior remaining empty as a
bladder, "the outer coat of the fruit only having been fertilized
in consequence of the weakness of the cross-bred pollen." {ih.^
p. 9.) In other cases, he comments, one may find a perfect ovary,
and seeds grown to full size, although "containing a perishable
lymph, and no sound kernel." It appears to Herbert that the fer-
tilization-process is one which may consist of gradual degrees,
and that "it follows therefore that a continued operation of the
pollen must be necessary to produce all these requisites for the
formation of a good seed." {ih.^ p. 9.) He speaks of the "fertiliza-
tion" of the seed-coats and of the "albumen" as a process inde-
pendent of the fertilization of the ovules, since the result of such
fertilization may cause the seeds to grow, although without de-
veloping an embryo. He finally concludes (p. 10) :

"if, therefore, as I apprehend, the pollen tubes cannot reach the ovules
without deriving substance from the cognate juices of the style through
which they descend, it becomes easy to understand how there may be
sufficient affinity between them to carry on the process to the degree
necessary for quickening the capsule, but not to carry it on to the point
requisite and with the excitement and irritability necessary for reaching
the ovules, etc."

Again, he continues, where adaptation of the two types is per-
fect, a perfect offspring is produced ; where it is not perfect, an
inadequate or weak fertilization occurs, and, "it is further to be
observed that there is frequently an imperfect hybrid fertilization
which can give life, but not sustain it well." Among these he
mentions Hibiscus palustris X speciosus^ of which the seeds al-
ways sprouted, but of which only one was saved to the third
leaf, when it perished. He states that of Rhododendron ponti-

100 PLANT HYBRIDlZx^TION BEFORE MENDEL

cum X ^^ orange Azalea he had never raised seedlings beyond

the third or fourth leaf. From Rhododendron canadense X Azalea

pontica, he succeeded in saving "only one out of more than a

hundred seedlings, and that became a vigorous plant." (jh.,

p. 11.)

He says further :

"In these cases I apprehend that, although the affinity of the juices is
sufficient to enable the pollen to fertilize the ovule, the stimulus is in-
sufficient, the operation languid, and the fertilization weak and inade-
quate to give a healthy constitution. It has been generally observed that
hybrid fertilization is slower than natural fertilization, and that often a
much smaller number of ovules are vivified." (p. ii.)

Herbert comments shrewdly on Knight's report as to having
"given at the same time the curl of one cabbage and the red color
of another to a third variety." (p. 12.) This Herbert considers
to have been impossible, if it was supposed to have been effected
by one fertilization.

"He might easily have obtained the twofold features by two successive
crosses, but I believe not in one generation by simultaneous application
of different pollens : for I do not think that two grains even of the same
pollen can get effectual access to the foramen of one and the same
ovule." {ib., p. 12.)

Herbert did much work, both of a systematic sort and by way
of crossing, upon the Amaryllidaceae, the species chiefly utilized
belonging to the genera Hippeastrum, Crinum and Hymenocallis^
the genus Narcissus being also rather extensively dealt with. In
December, 1819, Herbert made a communication to the Horticul-
tural Society of London (Vol. 4, pp. 15-50), entitled "On the
production of hybrid vegetables ; with the result of experiments
made in the investigation of the subject," in which a number of
observations are made of some genetic value. For the most part,
the article consists of an account of various interesting crosses
with a number of genera of ornamental bulbous plants, together
with some discussion of the species question, and of the fact of
sterility in certain crosses. The case is reported of a cross by
Knight, between a smooth cabbage (female) and a curled and
red cabbage (male), in which the curled leaf character and the
red color both appeared in the seedlings. The state of knowledge
concerning fertilization is indicated by Herbert's discussion of
the subject. Seeds originally exist in the "germen." During the
maturation of the stigma, the germen and seeds grow until the

PLANT HYBRIDIZATION BEFORE MENDEL loi

stigma reaches maturity, when the "germen" generally ceases to
grow, and unless it receives the "congenial dust" it fails. Herbert
then raises the question, how it is that a seed can draw from the
plant the nourishment necessary for its growth up to a certain
point, and yet be unable to obtain the further support necessary
to bring it to maturity. His opinion follows :

"I suspect the fact to be," he says, "that as long as the style remains
fresh the seed receives a portion of its nourishment by a return of the
sap from the style and stigma ; and thus continues to advance rapidly
in growth without any fecundation : but I apprehend that, during that
period, it is only that part of the seed, which is to form the cotyledon,
or seedling leaf, that grows, and that the actual germ of the young plant
does not exist completely till after the fecundation of the stigma, when
I conceive it to be actually formed by an union of the substance trans-
mitted through the vessels of the style, and that which was already
with the cotyledon, and thus partake of the type of both parents."
(2a, p. 29.)

"If," Herbert further comments, "the fecundation only gave
the embryo a stimulus to excite it to draw nourishment," then, the
male type would not be evident in the offspring. He further de-
cides upon the necessity of the pollen as the source of the male
contribution, on the basis of the fact which he had observed that,
in the case of seeds apparently perfect, where the stigma had not
been pollinated, or had been pollinated with pollen from a plant
not sufficiently related,

"on opening such seeds, there is a total deficiency of the germ, the
seed being an inert lump, which cannot vegetate." (2a, p. 29.)

Herbert alludes to the idea, which he says was somewhat
prevalent, that if plant hybrids are fertile, their progeny will re-
vert to the type of the female parent. (2a, p. 40.) This he holds
to be extremely improbable, and, if true, almost inexplicable, the
reason being that, if fertile, they can be fecundated by pollen
from either parent.

The careful perusal of the entire body of William Herbert's
contributions shows the operation of a careful, logical, strong, and
able mind, which, within the entire limit of its opportunity, made
thorough and conscientious efforts in the breeding of plants, and
secured considerable results of much interest, and made many
acute and shrewd observations of a botanical nature.

The services which Dean Herbert rendered plant breeding, con-
sisted notably in the clear and intelligent manner in which he

102 PLANT HYBRIDIZATION BEFORE MENDEL

contended, contrary to Knight and many others, that species and
varieties were but arbitrary and artificial distinctions in the plant
kingdom, so far as hybridization was concerned, and that the idea
of determining whether "species" were such, or only "varieties,"
through the relative fertility of their hybrid offspring, was an
error, since

". . . species and varieties are but intergrading types. The species of
botanists and the permanent local varieties are not essentially different
in their nature, but are variations induced by causes more or less remote
in the period of their operation, though the features of their diversity
may be severally more or less important, and they differ from accidental
varieties in the permanent habit of similar reproduction, w^hich they have
acquired from soil and climate, and that after a long succession of ages."

He was a close and keen observer, inclining toward experi-
mentation with ornamental flowers, as did Knight toward ex-
periments with horticultural fruits. He also calls for mention as
the first English-speaking investigator to notice the work of Kol-
reuter.

14. John Goss and Alexander Seton.

Besides the work of Knight and Herbert, an experiment with
garden peas from the first half of the nineteenth century, which
has elicited considerable interest, also because of its suggestion
of the later discoveries of Mendel, is that of John Goss, of Hath-
erleigh, in Devonshire, England.

In the summer of 1820, Goss pollinated flowers of the "Blue
Prussian" variety with pollen of a dwarf pea known as "Dwarf
Spanish," obtaining, as the result of the cross, three pods of
hybrid seeds. In the spring of 1821, when he opened these pods
for planting, he was surprised to find that the color of the seeds
(i.e., of the cotyledons), instead of being a deep blue like those
of the female parent, was yellowish-white like that of the male.
Here was evidently a case of complete dominance of yellow-white
over blue cotyledons. However, the plants growing from these
seeds "produced some pods with all blue, some with all white,
and many with both blue and white seeds in the same pod." Here
was evidently a plain discovery of the fact of segregation, accord-
ing to what later became known as Mendel's law. The following
spring (1822) he separated the blue peas from the white, sowing
the seeds of each color in separate rows. He found the blue seeds.

PLANT HYBRIDIZATION BEFORE MENDEL 103

which would now be called the recessives, produced in turn only
blue seeds, while the white seeds, or dominants, "yielded some
pods with all white, and some with both blue and white peas
intermixed." Here, then, is the typical case of the segregation
from the heterozygotes of hybrid dominants, without of course
statistical data.

Although Goss, in this experiment, undoubtedly made evident
the facts of dominance and segregation, he did not recognize them
as such, nor did he apparently, sow the seeds of his different
plants separately, or make counts as did Mendel, of the numbers
of seeds of the two colors found on each separate plant. Goss was
chiefly interested in the question of the possibility of the "new va-
riety" having superior value as an edible pea, and remarked that,
in case it possessed no superior merit, there might yet be "some-
thing in its history that will emit a ray of physiological light."
However, the "physiological light" did not appear until after the
rediscovery of Mendel's papers in 1900. The paper of John Goss
was read before the Horticultural Society, October 15, 1822. (i.)

At the meeting of the 20th of August preceding, a communica-
tion was read on the same subject from Alexander Seton. Seton
had pollinated the flowers of the "Dwarf Imperial," a green-
seeded pea, with the pollen of a tall white-seeded variety. One
pod with four peas was produced, all of which were green, pos-
sibly the dominance of green cotyledon color over its absence
(white). The plants growing from the four peas (F^ seeds) were
intermediate in size between the two parents ; and the pods, on
ripening,

". . , instead of their containing peas like those of either parent, or of
an appearance between the two, almost every one of them had some peas
of the full green color of the Dwarf Imperial, and others of the whitish
color of that with which it had been impregnated, mixed indiscrimi-
nately, and in undefined numbers ; they were all completely either of one
color or of the other, none of them Waving an intermediate tint." (5,
P- 237-)

Here again are recorded the phenomena of dominance and of
segregation, but owing to the fact that the numbers of the seeds
were not counted, the results were not available for scientific
purposes, nor would they have aroused attention, any more
than those of Goss, except for Mendel's work later.

104 PLANT HYBRIDIZATION BEFORE MENDEL

15. The Experiments of Thomas Laxton.

In 1872, Thomas Laxton published, in the Journal of the
Royal Horticultural Society, results of hybridization experiments,
entitled "Notes on Some Changes and Variations in the Offspring
of Cross-fertilized Peas" (4b), which have several points of dis-
tinct interest: first, in that the fact of dominance in color and
form of the seeds was brought out; second, from the fact that,
to a certain limited extent, a statement of numerical results was
attempted. The results in neither of these were sufficient to con-
stitute a scientific experiment, but the work as a whole gives
evidence of care, close observation, and some thought. Among
the several reported pieces of experimental work with peas before
Mendel, Laxton's is perhaps to be commended as being more
nearly of an exact nature, and is also interesting from the fact
that it constitutes the last experimental work in the hybridization
of peas, published before the final re-appearance of Mendel's
papers themselves. Laxton says :

"since the year 1858, I have been carrying on continued and successive
courses of experiments in cross-fertilizing the cultivated varieties of the
Pea, partly with a view to produce improved characters, and partly for
the purpose of noting the results of artificial impregnation on a genus
of plants, which, although not absolutely beyond the reach of accidental
cross-fertilization, is, for most practical purposes, sufficiently free from
it to make the changes produced by artificial impregnation approximately
reliable, at all events more so than in the majority of genera." (4b, p. 10.)

Laxton, at the time of his experiments, was not aware of the
work of Knight with peas some fifty years previously.

In 1866, a cross was made upon an early, white-flowered variety,
known as "Ringleader," with round, white seeds, and growing to
a height of about 2^ feet, by a purple-flowered variety known as
"Maple," with slightly indented seeds, and taller than the pre-
ceding. This produced one pod, containing five round, white peas
like those of the female parent, the ordinary result. The seeds of
the parent variety known as "Maple" are not described, but the
results leave it to be inferred that the seed-coat color was grayish-
purple, whence the name. In 1867, the five seeds of the F^ gen-
eration produced "tall, purple-flowered, purplish-stemmed" plants,
and the seeds, "with few exceptions," had "maple or brownish-
streaked seed-coats." The remainder are reported with "entirely
violet or deep purple-colored envelopes" (the ordinary dominant
for seed-coat color in the F^). The dominance of roundness in

PLANT HYBRIDIZATION BEFORE MENDEL 105

the first generation was followed in the second (the F^ for the
seed-coats) by segregation, which is recorded by Laxton, to the
effect that "in shape, the peas were partly indented ; but a few
were round." (4b, p. 11.)

The lack of a proper ratio in this case, of 3 round to 1 in-
dented, was probably due to the small number of plants involved.

In 1868 (the Fo for flower and seed-coat color), Laxton says:

"Some of the plants had light-colored stems and leaves; these all
showed white flowers and produced round white seeds. Others had purple
flowers, showed the purple on the stems and at the axils of the stipules,
and produced seeds with maple, grey, purple-streaked, or mottled, and
a few only, again, with violet-colored envelopes." (4b, p. 11.)

It is further stated that:

"The pods on each plant, in the majority of instances, contained peas
of like characters ; but in a few cases the peas in the same pod varied
slightly, and in some instances a pod or two on the same plant contained
seeds all distinct from the remainder." (4b, p. 11.)

It is reported that the white-flowered plants of the Fo were

"generally dwarfish, of about the height of 'Ringleader,' but the colored-
flowered sorts varied altogether as to height, period of ripening, and color
and shape of seed." (p. 11.)

There would appear to be here some evidence of partial link-
age of height with white flower and seed-coat color.

The outline of the results of Laxton's cross, stated in modern
terms, is as follows :

1866 Parents

''Ringleader' "Maple'

Flowers — white Flowers — purple

Seed-coats — white Seed-coats — "maple"

Cotyledons — round Cotyledons — indented

Height — 2i^ feet Height — taller than "Ringleader"

Progeny

1866. F, (for cotyledons)
Cotyledons — round

1867. F, (for flower color and seed-coat color)
Flowers — purple

Seed-coats

(1) (2) ("a few")

Maple or brownish-streaked Violet or deep purple

Cotyledons — partly indented ; a few round
Height — tall

io6 PLANT HYBRIDIZATION BEFORE MENDEL

1868. F,

(,) (2) ("a few only")

Flowers — purple Flowers — purple

Seed-coats — maple-grey, purple- Seed-coats — violet
streaked, or mottled

Cotyledons — round or partially Cotyledons — round or partially in-
indented dented

Height — variable Height — variable

(3)
Flowers — white
Seed-coats — white
Cotyledons — round
Height — same as "Ringleader"

(4) (on some of the purple-flowered plants)

(4—0 (4—2)

Seeds not described; presumably (A few pods on each plant)

shades of maple, etc. Seed-coats all white (some pods)

Seed-coats black (others)
Seed-coats violet (a few)

1869. F3

Progeny of (1)

(1 — 1) ("majority") (1 — 2) (minority)

Flowers — purple Flowers — purple

Seed-coats — purple or grey Seed-coats — maple or brown-

streaked
Cotyledons — round or only par- Cotyledons — round or only par-

tially indented tially indented

Progeny of (2)
(2 — 1) ("almost invariably") (2 — 2) ("now and then")

Flowers — purple Flowers — purple

Seed-coats — purplish-grey, or maple Seed-coats — clear violet ("either

wholly in one pod, or only a
single pea in a pod")

Cotyledons — round or only par- Cotyledons — round or only par-

tially indented tially indented

Progeny of (3) (all)

Flowers — white
Seed-coats — white
Cotyledons — round

As the seeds of the F2 generation (reported as a "few only"),
with "violet-colored envelopes," as distinguished from the ma-
jority having maple-grey and mottled seed-coats, these, when
again sown, are reported as producing "nearly all maple or
particolored seeds, and only here and there one with a violet-

PLANT HYBRIDIZATION BEFORE MENDEL 107

colored envelope." The violet seed-coat color is also reported as
having "appeared only incidentally, and in a like degree in the
produce of the maple-colored seeds." (4b, p. 11.)

In the following year, 1869, the seeds of the different types
of the preceding year were again sown separately. The white-
seeded peas again produced only plants with white flowers and
round white seeds. Some of the colored seeds, which Laxton said
he had expected would produce purple-flowered plants, produced
plants with white flowers, and round, white seeds only (in other
words recessives). The majority of the colored seeds, however,
produced plants with purple flowers, and seeds "principally
marked with purple or grey, the maple or brown-streaked being
in the minority." {ib.^ p. 11.)

It is stated that in some pods the seeds were all white, in others

all black, and in a few all violet, and again that:

". . . those plants which bore maple-colored seeds seemed the most
constant and fixed in character of the purple-flowered seedlings; and
the purplish and grey peas, being of intermediate characters, appeared
to vary most. The violet-colored seeds produced almost invariably pur-
plish, grey or maple peas, the clear, violet color only now and then ap-
pearing, either wholly in one pod, or a single pea or two in a pod."
The purple-flowered plants are stated to produce from the 1869 sowing,
seeds that were "either round or only partly indented," the plants vary-
ing as to height and time of maturity, {ib., p. 12.)

Laxton also records the important fact that

"in no case, however, does there seem to have been an intermediate-
colored flower ... I have never noticed a single tinted white flower
nor an indented white seed in either of the three years' produce." {ib.,
p. 12.)

The quantities of the different colors produced in the seeds of

the 1869 plants, are reported as being, in order of their amounts,

as follows :

"First, white, about half; second, purplish, grey, and violet (inter-
mediate colors) about three-eighths ; third, maple, about one-eighth."
(p. 12.)

True ratios are, of course, not derivable, on account of the
small numbers involved. Laxton's own conclusion as to the par-
ental types is as follows :

That the white-flowered, white-seeded pea is "an original variety, well
fixed and distinct entirely from the maple, that the maple is a cross-bred
variety which has become somewhat permanent and would seem to in-
clude amongst its ancestors one or more bearing seeds either altogether
or partly violet- or purple-colored." {ib., p. 12.)

io8 PLANT HYBRIDIZATION BEFORE MENDEL

From Laxton's cross of 1866, it appears that dominance of
round form for cotyledons was evident in the cross, since he says :

"This cross produced a pod containing five round, white peas, exactly
like the ordinary 'Ringleader' seeds." {ib., p. 10.)

Purple flower color, and color in the seed-coats, was dominant
in the 1867-grown plants.

The seed-coat color of the F^^, however, which was "maple" in
the male parent, split into maple (the majority), and violet or
deep-purple (a few), in the following generation, grown in 1868.

The F2 progeny, in 1868, split up into plants with purple
flowers and colored seed-coats, and a recessive with white flowers
and white seed-coats, which latter bred true in 1868 and 1869.
Of the purple-flowered progeny of the F2, the seed-coats were
mostly- maple or some modification of it. A few had violet seed-
coats. The former, in 1869, split into a majority with seed-coats
purple or grey, and only a minority maple or brown-streaked.
The "few" in the F2 with violet seed-coats, split, in the F3, into
(almost entirely) purplish-grey or maple, with occasional ones
violet again. Without further speculation as to the probabilities
in respect to the original maple seed-coat color, which Laxton
was dealing with in the male parent of the cross, the facts above
are given for whatever interest they may have. It should be men-
tioned that the seeds, in what we know as the Fg generation, are
described as being "partly indented, a few round." It is not clear
whether Laxton meant by "partly indented," the same thing as in
the description "slightly indented,"' by which the seeds of the
original "Maple" parent are described. It may be taken to mean
simply that a part of the seeds were indented ; a few round. The
expectation would have been, "mostly round, a few indented,"
to use Laxton's manner of describing.

The dominance of taljness in the F^ is shown, and the clear
segregation out of dwarf with white flower color and white seed-
coats in the F2.

Laxton adds that he had derived from his experiments the
same conclusion as Knight and others:

"That the colors of the envelopes of the seeds of peas immediately
resulting from a cross are never changed." (p. 12.) He states also: "I
find, however, that the color and probably the substance of the cotyle-
dons are sometimes, but not always, changed by the cross-fertilization
of two different varieties." (p. 12.)

PLANT HYBRIDIZATION BEFORE MENDEL 109

One of the most striking features of Laxton's paper is the fol-
lowing remarkable, detailed observation, distinctly Mendelian in
character, and one which should entitle the paper to especial in-
terest.

He says :

"l have also noticed that a cross between a round white and a blue
wrinkled pea, will in the third and fourth generations (second and
third year's produce) at times bring forth blue round, blue wrinkled,
white round, and white wrinkled peas in the same pod, that the white
round seeds when again sown, will produce only white round seeds, that
the white wrinkled seeds will, up to the fourth or fifth generation, pro-
duce both blue and white wrinkled and round peas, that the blue round
peas will produce blue wrinkled and round peas, but that the blue
wrinkled peas will bear only blue wrinkled seeds." (p. 13.)

There does not exist anywhere, in the pre-Mendelian literature,
any other similar, clear, distinct, or detailed statement of an ob-
servation of segregation involving two pairs of characters. So far
as it has come to the knowledge of the writer, there exists no
similar observation, or one of equal value, or so closely approxi-
mating an analytical statement, preceding Mendel's account.

It is interesting to trace, in Laxton's conclusions from the
above, the manner in which the logic of the situation appealed to
his mind.

"This would seem to indicate," he says, "that the white round
and the blue wrinkled peas, are distinct varieties derived from
ancestors respectively possessing only one of these marked quali-
ties." (p. 13.)

This in itself is a genetic conclusion. In Mendel's case, such
a fact pointed to the purity of the gametes. To Laxton's mind,
it indicated a pure line of similar ancestors — the same thing in
principle, but less analytically stated. Laxton is interested more
in the ancestors than in the manner of transmission ; Mendel in
the mechanism of the transmission itself. Thus Laxton says:

"In my opinion the white round peas trace their origin to a dwarfish
pea having white flowers and round white seeds, and the blue wrinkled
varieties to a tall variety having also white flowers, but blue wrinkled
seeds." (p. 13.)

One of the principal objectives of the early breeders was to
ascertain when and how a "variety" could be "fixed." Laxton con-
cludes that three or four years is

", . . the shortest time which I have ascertained it takes to attain the

no PLANT HYBRIDIZATION BEFORE MENDEL

climax of variation in the produce of cross-fertilized peas, and until
which time it would seem useless to expect a fixed seedling variety to
be produced, although a reversion to the characters of either parent, or
any one of the ancestors, may take place at an earlier period." (p. 13.)

Laxton's purely botanical attitude toward the matter is well
brought out in his final statement :

". . . in conclusion I may, perhaps, in furtherance of the objects of
this paper, be permitted to inquire whether any light can, from these
observations or other means, be thrown upon the origin of the cultivated
kinds of peas, especially the 'maple' variety, and also as to the source
whence the violet and other colors, which appear at intervals on the
seeds and in the offspring of the cross-fertilized purple-flowered peas,
are derived." (p. 14.)

16. The Experiments of Patrick Skirreff.

Before closing an account of the early English hybridizers,
it is proper to add an account of the work carried on in the
breeding of wheat by Patrick Shirreff of Scotland, recorded in his
brief memoir, "Improvement of the cereals and an essay on the
wheat-fly," published at Edinburgh and London, in 1873. These
experiments began in 1819, with a series of pure line selections
of wheat and oats, and concluded with hybridization experiments.

The fact that Shirreff appears not only to have been the first
experimenter of any consequence with the cereals to follow the
principle of selecting only pure lines, and the fact that he was
the first considerable hybridizer of wheat, make it desirable to
include an account of his series of experiments for the sake of
their historical value, as well as because of their not inconsid-
erable practical success. The circumstance that dominance in cer-
tain cases was reported, even if not further commented upon, is
interesting as a matter of record.

In the spring of 1819, when walking over a field of wheat, on
the farm of Mungoswells, in the County of Haddington, Scot-
land, Shirreff noticed "a green spreading plant" which attracted
his notice, "the crop then looking miserable from the effects of
a severe winter." At harvest time 63 heads were harvested, yield-
ing 2,473 grains. These were dibbled in, the following autumn,
at wide intervals. For two succeeding seasons, the seed was sown
broadcast, and the first harvest of the progeny of the original
plant amounted to 336 bushels.

In the summer of 1824, "a tall oat plant was observed on a

-ii-f-^^.

Plate XXV. Patrick Shirreff.

112 PLANT HYBRIDIZATION BEFORE MENDEL

field of the cereal, on the farm of Mungoswells." (6, p. 2.) The
seeds from this plant were grown in a collection of named vari-
eties. At harvest, the crop from the plant proved to be the tallest
in the collection. The variety was then raised, and introduced
under the name of Hopetoun oat.

In the fall of 1832 "a fine ear of wheat was found on the farm
of Drum, which adjoins Mungosv/ells. This ear originally con-
tained one hundred and two grains." The progeny from the head
became the Hopetoun wheat.

"The grain is rather large, white and heavy, the ear is handsome and
its chaff white." ... (6, p. 4.)

"This variety found its way into many of the wheat-growing districts
of Britain, and over a wide range of country and climate. It succeeded
better than some of the white varieties originated in Scotland, which
became so high colored when grown in the south of England, as not to
be classed in that country as white wheat." {ib., p. 4.)

"The next cereal," ShirrefT says, "which I selected, raised and intro-
duced into full practice, was the Shirreff oat, which ripens early, and is
reported to be very prolific." {ib., p. 5.)

"Hitherto," he remarks, "I had followed the improvement of the
cereals by fits and starts, on the spur of the moment; but in 1856, some-
thing like a continued and systematic investigation of the subject was
begun." (p. 5.)

He proceeded to examine the wheat fields on both sides of the
Tweed, especially in East Lothian, and selected many heads
which differed from the general crop.

"My experimental plot of wheat for 1857," he says, "contained plants
from the seeds of more than seventy ears, which had been selected dur-
ing the previous years." {ib., p. 6.)

From the many strains originating from the first year's selec-
tions, three kinds only were propagated. The names given to
them were "Shirreff's Bearded Red," "Shirreff's Bearded White,"
and "Pringles."

Shirreff now found that the limitations of time and space
made it necessary to restrict the number of strains experimented
with. The following interesting account is given of what is prob-
ably the first systematic planting of plots for the experimental
growing of pure strains of wheat.

"My comparative trial-plot of wheat might be described thus: On a
field cropped with wheat, named and unnamed varieties were grown in
parallel pairs, from twelve to fifteen feet long, and from nine to twelve
inches broad, with a foot-path a yard wide, surrounding the whole
plot. . . . From time to time, notes were made regarding each kind,

PLANT HYBRIDIZATION BEFORE MENDEL 113

such as their time of ripening, length of stem, etc. By such means, the
new varieties could be more readily distinguished from the old, and
twice-naming detected, as the effects of soil and seasons upon the differ-
ent kinds approximated. . . . Then, commencing on one side, the seeds
were placed by the hand at a given thickness, and each variety covered
with earth before another was planted. By proceeding in this manner,
the seeds were placed in the soil at nearly equal depths and distances,
and the different varieties kept from intermixing in the process of sow-
ing." {ib., pp. 8-9.)

By i860, "Shirreff's Bearded Red" had increased until it
amounted to twelve acres.

In i860, the trial wheat plots contained seed from eighty-four
heads. By this time, Shirreff had become well known, so that
heads of wheat were being sent to him by many persons from
different places, the seeds of which found their way into his
experimental plots.

"In 1862, an attempt was made to improve oats." (p. 12.)
From fields in the neighborhood of Haddington selected heads
were taken. In 1864, the more promising kinds were included in
this trial plot along with eighteen named varieties. Ultimately,
four of the selections were propagated, under the names of "Early
Fellow," "Fine Fellow," "Long Fellow," and "Early Angus."

Shirreff had by this time come to the following conclusion :

"Many people believe that some plants can be altered by skilful
treatment, but my experience had tended to show that there is no way
of permanently improving a species but by a new variety. In support
of the view of plant improving, gardeners can point to- hosts of new and
improved varieties of fruits, vegetables, and flowers, while, to corrobo-
rate, farmers can bring forward the Chevalier Barley, Swede Turnip,
Italian rye-grass and the Alsike Clover. To this' principle of improvement
the cereals form no exception ; and the small amelioration which they
have undergone in this age of progress, may fitly be attributed to the
apathy of corn growers in this department of agriculture." {ib., pp. 14-18.)

"New varieties of the cereals," Shirreff says, "can annually be obtained
from three sources — from crossing, from natural sports, and from for-
eign countries." {ib., p. 18.)

Shirreff's technique in the crossing of wheat may be of interest
to breeders of this cereal.

"Before commencing to cross," he says, "consider what properties the
new variety is wished to inherit; and fix upon such kinds as possess in
the highest degree the desired properties." {ib., p. 22.)

A day or two after the head emerged from the sheath, the head
was shortened, every alternate spikelet was removed, and only
the two lateral or outside flowers of each spikelet were allowed

114 PLANT HYBRIDIZATION BEFORE MENDEL

to grow. Such a head would consist of four to six spikelets with
eight to twelve flowers. The head of the plant intended to be used
as the pollen parent was then brought, the anthers removed from
the flowers of the proposed female parent, and the anthers from
the head of wheat intended for the male parent were removed and
placed within the glumes of the emasculated flower. It was recom-
mended that two persons work in cooperation, one to hold open
the chaff-scales or glumes, the other to remove and replace the
anthers with a pair of forceps. The head thus pollinated was
then fastened to a stake and enveloped in wire gauze as protec-
tion against being rubbed against by other heads, and against
birds. It is interesting to note the subsequent care with which the
hybrid seeds were treated :

"As soon as the grains obtained by crossing become dry, place them
in thumb pots in a garden, protecting them from birds and insects by
sprigs of furze spread on the surface, and by a few coal ashes in the
bottom, and afterwards remove the plants to where they were intended
to be grown. This plan prevents the intermixing of kinds, and generally
the attacks of insects residing in the soil, or frequenting the air, in the
early stages of the plants' growth." {ib., p. 24.)

"The inflorescence of oats and barley being wintered with wheat, the
crossing of these cereals can be effected in like manner as with wheat."
{ib., p. 24.)

. Knight's experiments in the crossing of wheat are quoted by
Shirreff as follows {ib., p. 27) :

"I readily obtained as many varieties as I wished, by merely sowing
the different kinds together; for the structure of the blossom of this
plant, unlike that of the pea, freely admits of adventitious farina, and
is thereby very liable to sport varieties. Some of those I obtained were
excellent, others very bad, and none of them permanent. By separating
the first varieties, a most abundant crop was produced, but in quality
was not equal to the quantity ; and all the discarded varieties again and
again made their appearance. It appeared to me an extraordinary cir-
cumstance, that in the years of 1795 and 1796, when almost all the whole
corn of the island was blighted, the varieties thus obtained only escaped
in this neighborhood when sown on different soils and situations."

Knight is referred to by Shirreff as "the first individual in
Britain known to have crossed wheat." {ib., p. 26.)

A Mr. Raynbird, who competed for a medal given by the High-
land Society of Scotland with a wheat obtained by hybridization,
known as "Raynbird's Hybrid," was, as Shirreff says,

". . . perhaps the first person who offered a hybrid or cross-bred wheat
to the notice of the British farmers." {ib., p. 8.)

PLANT HYBRIDIZATION BEFORE MENDEL 115

Regarding his own crossing Shirreff says :

"One of my first attempts at crossing was made with April and Tala-
vera varieties, the latter being the pollen parent."

Regarding the hybrid he says :

"The plant from cross-fecundation appeared to be an intermediate
between the breeders." {ib., p. 28.)

Between Shirreff's first and second attempts at the crossing of
wheat a period of nearly twenty years intervened.

The technique developed by Shirreff in his wheat crossing ex-
periments is further described as follows :

"The valves of the chaff were opened, and the anthers removed one
by one with the point of a needle. Three or four days afterwards, accord-
ing to the state of the weather, the valves of the chaff were again opened,
and the stigma touched with a camel's-hair brush covered with pollen
from the anthers of the male breeder. From the opening and closing of
the chaff valves," Shirreff says, "they frequently dropped off after fe-
cundation had been effected ; and scarcely one attempt in ten ended suc-
cessfully until the method described at page 21 was adopted, which so
changed matters that three attempts out of four proved successful."
{ib., pp. 29-30.}

"For some time," Shirreff says, "my cross-fecundations produced noth-
ing very striking, until a variety in my comparative trial-plot attracted
notice, from the size of ear, and the length and strength of the straw,
when ripe, the grains were found to be fine in quality, and it was de-
cided to raise a stock from it for field practice." (ib., p. 31.)

The variety in question was produced by crossing "Shirreff's
Bearded White" with pollen from "Talavera," with a view to
enlarging the seeds of the Bearded White, which were small and
round. The hybrid was called "King Richard," and was found
to be intermediate between the parents in form of ear, while ap-
proaching the Talavera in size and form. In tillering habit it was
intermediate.

Shirreff, of course, knew nothing of the laws of segregation,
and a hybrid once obtained was for him always a hybrid. The
"mixed ears," spoken of as appearing in the progeny, were prob-
ably the segregating forms. Shirreff s^ys :

"These mixed ears in all probability are owing to the hybridous
origin of King Richard, and are not likely to be got rid of without rais-
ing a stock again from a single grain, and when necessary doing so again
and again." {ib., p. 31.)

By such selection he originated a new strain called "King Red
Chaff White," which was exhibited in bulk for the first time in
1870. Regarding it he says:

ii6 PLANT HYBRIDIZATION BEFORE MENDEL

"Altogether, I am at present disposed to regard King Red Chaff White
as perhaps one of the best wheats I have sowed." {ib., p. 3.)

Shirreff also crossed Talavera, which has white chaff, with a
variety with small white seeds and red chaff. In this hybrid he
makes perhaps the first reference to color dominance in the chaff
of wheat.

"The plant from the seed, in form of ear and seed, closely resembled
Talavera, but the color of the chaff was red." (ib., p. 33.)

The dominance of downy chaff over smooth chaff, was also
recorded as follows :

"A downy-chaffed variety with tall straw, which had been selected
from Hopetoun, was fecundated with pollen from Talavera, and the re-
sult was a constant variety with the downy chaff and fine straw of the
seed parent." (ib., p. 33.)

Shirreff records (pp. 34-5) his observations on the natural
crossing of wheat in the field.

"Having satisfied myself of the possibility of changing the seeds and
external characteristics of the wheat plant by crossing, I resolved to
attempt altering the habit of ripening." {ib., p. 36.)

For this purpose he used a spring wheat known as Tuscany,
brought originally from New Zealand. Tuscany wheat was found
to ripen eight or ten days earlier than other kinds grown by him.
In 1869, he crossed Tuscany with King Richard and with Tala-
vera, with the object of improving the straw and grain of the
former variety, but of introducing its earlier ripening. From the
cross with King Richard he obtained earlier seeds, which were
planted in thumb pots. These were taken to the field, and six
plants finally came to harvest. The cross from Tuscany with
Talavera produced one plant. In 1811, these first-generation
hybrids were harvested. Shirreff, of course, assumed that the new
types thus appearing were as likely to be fixed in type as the
parents.

Shirreff records, that of the seven first-generation hybrids, five
were summer and two winter wheat. Out of over eighty wheat
plants resulting from hybridization, he reports that he grew, in
1872, upwards of forty.

As to the seldom occurrence of natural crossing, Shirreff notes :

"if varieties growing contiguous are always instrumental in fecunda-
ing one another, my experimental plots must have long since become a

PLANT HYBRIDIZATION BEFORE MENDEL 117

heterogeneous mass, when between one and two hundred sets have been
grown within a foot of each other for nearly fourteen years."

ShirrefF remarks pointedly upon the necessity for the final test
of the product, as the criterion of science In the improvement of
wheat.

"One of the chief difficulties which an individual experiences when
improving the plant, is to ascertain the quality of the grain or the flour
produced from it. . . . In an inquiry of this nature, the aid of the
chemist is thought to be of little avail, and the baker's bread, taking
color, quality, and quantity into consideration, is a more satisfactory
test to the farmer." (p. 62.)

"In carrying out the improvement of cereals, the selecting of varieties
may be considered an important step; and the object in all probability,
will be sooner accomplished and better controlled, by first creating a
diversity, which can easily be effected by crossing. . . . Crossing tends
to produce variation in kinds not given to sporting, and in this respect
it has much advantage over the system of improvement by merely select-
ing from the crops of the farm. A new and important source of varia-
tion is opened up by crossing, but a judicious improver of the cereals
will never overlook this interesting proceeding. Always cross with the
seedlings which inherit in the greatest degree the properties you wish
a cereal to possess, and by persevering for a series of years to select,
and by crossing in this manner, success in all probability will be ulti-
mately attained." (p. 95.)

BIBLIOGRAPHY

1. Goss, John.

On the variation in the color of peas, occasioned by cross-
impregnation. Transactions of the Horticultural Society of
London, 5:234, 1824.

2. Herbert, William.

(a) On the production of hybrid vegetables, with the result
of many experiments made 4n the investigation of the
subject. Transactions, Horticultural Society of London,
4:15-50, 1819.

(b) On crosses and hybrid intermixtures in vegetables, pp.
335-80 fat end of 2c).

Ii8 PLANT HYBRIDIZATION BEFORE MENDEL

on cross-bred vegetables, and supplement, pp. 1-334-
London, 1837.
(d) On hybridization amongst vegetables. Journal of the
Horticultural Society. 2:1-28, 81-107. 1847.

3. Knight^ Thomas Andrew.

(a) An account of some experiments of the fecundation of
vegetables. Philosophical Transactions, Royal Society of
London, Part I, pp. 19^-204. 1799.

(b) Observations on the method of producing new and early
fruits. Transactions, Horticultural Society of London,
l:pp. 30-40. November 4, 1806.

(c) On the comparative influence of male and female par-
ents on their offspring. Transactions, Royal Society,
1 :pp. 392-9, 1809. Read June 22, 1809.

(d) Observations on hybrids. Transactions, Horticultural
Society of London, 4:367-73, 1821.

(e) An account of some mule plants. Transactions, Horti-
cultural Society of London, 5:292-6, 1823.

(f) Some remarks on the supposed influence of the pollen,
in cross-breeding, upon the color of the seed-coats of
plants, and the qualities of their fruits. Transactions,
Horticultural Society of London, 5 '377-80, 1823,
June 3.

(g) A selection from the physiological and horticultural
papers published in the Transactions of the Royal and
Horticultural Societies, by the late Thomas Andrew
Knight, to which is added a sketch of his life. London,
1841.

4. Laxton^ Thomas.

(a) Observations on the variations effected by crossing in
the color and character of the seed of peas. Report of the
International Horticultural Exhibition and Botanical
Congress, May 22-31, 1866. (p. 156.)

(b) Notes on some changes and variations in the offspring
of cross-fertilized peas. Journal of the Royal Horticul-
tural Society, 3:10-14, 1872.

PLANT HYBRIDIZATION BEFORE MENDEL 119

5. Seton, Alexander.

On the variation in the color of peas from cross-impregna-
tion. Transactions of the Horticultural Society of London,
5:236, 1824.

6. Skirreff, Patrick.

Improvement of the cereals and an essay on the wheat fly.
Edinburgh and London, 1873.

CHAPTER V

THE WORK OF THE FRENCH HYBRIDISTS

17. The Experiments of Sageret.

DURING the time of the prosecution of the work of Knight
and Herbert there appeared the results in hybridization
obtained by Sageret in France.

Augustin Sageret was born at Paris, July 27, 1763. He was a
naturalist and practical agronomist, was one of the founders of
the Society of Horticulture of Paris, and a member of the Royal
Society of /\griculture, afterwards called the Academy of xAgri-
culture. He was author of an agronomic survey of the canton of
Lorris, where he settled at the age of fifty-six, to take up and
bring into condition an agricultural domain of 750 acres. He
had the honor of having the genus Sageretia named after him by
Brogniart. His death occurred in 1851.

Sageret's experiments in crossing were largely confined to the
Cucurbitaceae, and his results were published in a memoir, en-
titled "Considerations sur la production des hybrides, des vari-
antes et des varietes en general, et sur celles de la famille des
Cucurbitacees en particulier," which appeared in 1826, in the
Annales des Sciences Naturelles, Yol. 8. (C-)

Sageret made some discoveries that clearly anticipate our mod-
ern knowledge of segregation, and he was able to furnish what
was, for the time, a fairly satisfactory scientific explanation for
the reappearance of ancestral characters. The experiment upon
which his conclusions were primarily based was a cross, in which
a muskmelon was the female, and a cantaloupe the male parent.
Each plant was regarded as a relatively pure type-representative
of its kind. In stating the results of the cross, Sageret for the
first time, so far as the writer knows, in the history of plant
hybridization, aligned the characters of the parents in opposing
or contrasting pairs, after Mendel's fashion forty years later.

PLANT HYBRIDIZATION BEFORE MENDEL 121

Following is the list of contrasting parental characters, as
Sageret gives them:

Muskmelon

Cantaloupe

(Female)

{Male)

flesh white

flesh yellow

seeds white

seeds yellow

skin smooth

skin netted

ribs slightly evident

ribs strongly pronounced

flavor sugary, and very acid at
the same time

flavor sweet

Sageret remarks :

"The assumed product of the crosses made ought to have been inter-
rnediate : 1 — flesh very pale yellow; 2 — seeds very pale yellow; 3 — net-
ting light ; 4 — ribs slightly marked ; 5 — flavor at once sweet and sprightly :
but the contrary was the case." (5, p. 303.)

As a matter of fact, in the two hybrid fruits reported upon, the
characters were not blended or intermediate at all, but were clearly
and distinctly those of the one or the other parent.

first hybrid second hybrid

1. flesh yellow 1. flesh yellowish

2. seeds white 2. seeds white

3. skin netted 3. skin smooth

4. ribs rather pronounced 4. ribs wanting

5. flavor acid 5. flavor sweet

In the further support of his conclusions regarding the descent
of characters in unitary fashion, he remarks upon the inheritance
of human hair and eye-color, in the mating of a brunette with a
blonde type.

Sageret remarks upon the fact that such hybrids are types, of
which he had "several times obtained the analogues or their
equivalent." While there is fusion here and there, he says, "one
sees here a much more marked distribution of their diflFerent
characters without any mixture between them." (5, p. 303.) He
even uses for the first time in the literature of plant hybridiza-
tion, the word "dominate" with reference to characters in cross-
ing, in the following words. Speaking of the inheritance of flavor
in various melon crosses, he says :

"The acid flavor of the muskmelon is encountered in the form of the
cantaloupe and the snake-melon ; in others, the form of the cantaloupe
dominated." (5, p. 307.)

Summing up the results of his experiments in a general con-
clusion, he says, with regard to the natural expectation that in

122 PLANT HYBRIDIZATION BEFORE MENDEL

a hybrid there will be a complete or partial fusion of the parental
characters, that:

"This fusion of characters may take place in certain cases ; but it has
appeared to me that, in general, things did not take place in this way,"
and again : "It has appeared to me that, in general, the resemblance of
the hybrid to its two ascendants consisted, not in an intimate fusion of
the diverse characters peculiar to each one of them in particular, but
rather in a distribution, equal, or unequal, of the same characters."
(5, p. 302.)

Here we meet, for the first time in the literature of hybridiza-
tion, the phrase "distribution of characters" now so familiar.
"These facts," Sageret remarks, "have been confirmed by a mul-
titude of my experiments."

It is evident, from the following statement, that Sageret ap-
praised his discovery of the dominance of characters in crossing
at its proper value :

"The ideas which I present," he says, "have appeared remarkable to
me ; they seem to me to be of a very great importance." (5, p. 302.)

In addition to his melon crosses, Sageret secured a hybrid be-
tween a black radish and a cabbage, of which he writes :

"Some of the fruits, instead of being intermediate, were like either
cabbage or radish on the same inflorescence." (5, p. 297.)

Each silique bore a single seed, analogous to its pod, to which
he makes reference in a further comment upon "the distribution
among hybrids of the characters of their ascendants without
fusion of these characters" (5, p. 304) — a point of view with
regard to the results of hybridization that needs little to make it
modern.

It is a matter of additional interest that Sageret was further
able to derive a natural scientific conclusion from the facts of
unit-character inheritance as he found them, with respect to the
reappearance of old or the appearance of new "species."

The hybrids "often reproduced for me," he says, "varieties
which had long ago disappeared." (5» p. 304-)

He finally concludes :

"To what, then, does this faculty belong, which nature has of repro-
ducing upon the descendants such or such a character, which had be-
longed to their ancestors? We do not know: we are able, however, to
suspect that it depends upon a type, upon a primitive mould, which
contains the germ which sleeps and awakens, which develops or not
according to circumstances, and possibly that which we call a new

PLANT HYBRIDIZATION BEFORE MENDEL 123

species is only an old species in which develop organs ancient but for-
gotten, or new organs, of which the germ existed, but of which the
development had not yet been favored." (5, pp. 304-5.)

The clear manner in which Sageret's mind rather instinctively
seized the conception of the independent descent of characters is
exemplified in a sentence in which he says that all plants, and
possibly still more, hybrid plants,

". . . having the ability to recall, so to speak at will, without measure
and indifferently, and independently of one another, the qualities of
their ascendants, it is possible that some among them, illy assorted,
should have left out all there was of good and have taken all there was
of ill." (5:308.)

18. Godron and Naudin on Hybridization.

In 1861, the Paris Academy of Sciences proposed the follow-
ing problem to receive the grand prize in the physical sciences :

"To study plant hybrids from the point of view of their fecundity,
and of the perpetuity or non-perpetuity of their characters.

"The production of hybrids amongst plants of different species of
the same genus is a fact determined long since, but many precise re-
searches still remain to be made in order to solve the following ques-
tions, which have an interest equally from the point of view of general
physiology, and of the determination of the limits of species, of the
extent of their variations.

1. "in what cases of hybrids are they self-fertile ? Does this fecundity
of hybrids stand in relation to the external resemblances of the species
from which they come, or does it testify to a special affinity from the
point of view of fertilization, as has been remarked regarding the ease
of production of the hybrids themselves?

2. "Do self-sterile hybrids always owe their sterility to the imperfec-
tion of the pollen *? Are the pistil and the ovules always suspectible of
being fecundated by a foreign pollen, properly selected? Is an appreci-
ably imperfect condition sometimes observed in the pistil and the ovules?

3. "Do hybrids, which reproduce themselves by their own fecundation,
sometimes preserve invariable characters for several generations, and
are they able to become the type of constant races, or do they always
return, on the contrary, to the forms of their ancestors, after several
generations, as recent observations seem to indicate ?"

The two chief competitors under the Academy's offer were
Charles Naudin, of the Museum of Natural History at Paris, and
D. A. Godron, of the University of Nancy, the prize being
awarded to the former. The papers of both appeared in Vol. 19
of the Annales des Sciences Naturelles (Botanique), 4me Serie,
1863. (2c, 4c.)

The title of Godron's thesis was, "Des hybrides vegetaux, con-

124 PLANT HYBRIDIZATION BEFORE MENDEL

siderees au point de vue de leur fecondite, et la perpetuite de

leurs characteres."

Godron.

Godron's paper is chiefly devoted to the solution of the question

". . . whether hybrids reproducing by self-fertilization sometimes keep
their characters invariable during several generations, and whether they
are able to become the types of constant races, or whether, on the con-
trary, they always return to the form of their ancestors at the end of
several generations, as recent observations seem to indicate."

Plate XXVI. D. A. Godron, 1807-1880, Professor at the University at Nancy.

PLANT HYBRIDIZATION BEFORE MENDEL 125
In answer to this query, he says :

"We have determined, upon hybrids of Linaria, that the hybrid forms
may become very fertile, and that a certain number of individuals from
the second generation return respectively to the two primitive types,

Plate XXVII. Charles Naudin, 1815-1899.

126 PLANT HYBRIDIZATION BEFORE MENDEL

when they grow In company with their parents, and this return move-
ment manifests itself much more in the following generations." (2c,
p. 174).

Godron remarks that the same fact has been observed by Lecoq
in the fertile hybrids of Mirabilis, by Naudin in the fertile hy-
brids of Nicotia7ia, and by several observers in Primula and in
Petunia.

From these experiments, then, he considers the proof of the
final return of fertile hybrids to their parental forms to be
established.

Godron was a victim of the rigid idea of species, which held
that, because so many hybrids between different "species," so-
called, were sterile, therefore any hybrid which turned out to be
fertile must necessarily, ipso facto, prove the parents not to be
of different species, but to be merely varieties of the same species.

To the vain purpose of settling this verbal controversy,
whether such and such plants were to be regarded as separate
"species," or merely as "varieties" of the same species, many of
the most ardent endeavors of hybridists, both before and since
Mendel's time, have been conscientiously and duly devoted. A
sample of this method of reasoning in a circle, so vigorously
combatted by Herbert, and characterized by him as "fighting the
air," is exemplified in a sentence of Godron's which typifies the
general view at that time. He speaks of a

"law which has its sanction in the numerous experiments which, for a
century past, have been made by Kolreuter, Wiegmann, C. F. Gartner,
etc., and by M. Naudin himself, that siinple hybrids are sterile or but
little fertile." (2c, p. 139.)

Considering the fact, however, that the hybrids between con-
fessedly distinct species are so frequently sterile, it is not sur-
prising that, in view of the then greater interest in the species
question itself, hybridizers should have turned systematic bota-
nists, and have made the sterility of the hybrid offspring a cri-
terion of species distinction.

Besides his competing memoir before the Paris Academy, God-
ron was the author of several other contributions to the literature
of plant hybridization, including that of the celebrated question
as to the possible origin of cultivated wheat from the wild plant
Aegilops ovata.

PLANT HYBRIDIZATION BEFORE MENDEL 127

In 1863, Godron (2) reported a series of observations upon
the fecundity of hybrids. He investigated the question whether
this fecundity, in succeeding generations, bore any relation to
the ease with which the original hybridization was effected. From
experiments with Verhascum hybrids he came to the conclusion
that the fertility of hybrids does not always have any relation to
the ease with which the cross is effected in the first instance.
From investigations which Godron made upon the cause of steril-
ity, he discovered that in some cases deformed and aborted pollen
was not, as frequently, the cause, but that perfectly formed pol-
len may be inactive. He raised the question whether

". . . the very great development which the organs of vegetation take
on in simple hybrids of Verhascum, the numerous branches and the im-
mense quantity of flowers which originate on these branches, would not
exhaust the vegetative juices at the expense of the organs of reproduc-
tion. Would there not be there a fact which the law of the balance of
organs would explain, the force of which one so frequently determines
as well in the plant as in the animal kingdom." (2c, p. 172.)

Godron concludes, in general, that crosses of two races or vari-
eties of the same species are characterized by absolute fertility,
that the sterility of the simple hybrids is proof that they come
from distinct species, and that crossing between two species of
different "genera" is impossible. We thus see the trend of God-
ron's mind — to establish by experiments in crossing the question
of what constitutes a species, a point of view that has entirely
disappeared today. At the present time, of course, no especial ac-
count is necessarily taken in crossing as to the precise systematic
position of the organisms which it is intended to cross. They may
be different "varieties," or different "species," or even belong to
different so-called "genera." Attention is necessarily directed pri-
marily to the nature of the characters which it is desired to in-
volve in the cross, the behavior of which it is sought to investi-
gate.

In his brief memoir, "Recherches experimentales sur I'hybridite
dans la regne vegetale" (2b), Godron discusses the question of
the fecundity of hybrids and the perpetuity or non-perpetuity of
their characters. He states that, from crossing experiments of his
own on species of the genera Verhascum^ Primula^ Nicotiana^
Digitalis^ Antirrhinum, Linaria, and Aegilops, "when two species,
incontestably distinct, are fecundated, the one by the other, they

128 PLANT HYBRIDIZATION BEFORE MENDEL

give products constantly sterile." (p. 228.) On the other hand,
he further comments (p. 254) :

"Crosses between two races or two varieties give, on the contrary, as
Kolreuter has established, and as all those have recognized who^ have
followed in his footsteps, products as fertile as legitimate species."

Godron's point of view as to the value attaching to hybrid
studies, is shown by his remark :

"This fecundity then, equal to that of the parents, characterizes crosses
(metis) and offers us a criterion to distinguish what is a race or a variety
from that which is a species." (p. 255.)

As to the fertility of hybrids and the perpetuity of their char-
acters, he cites especially the case of Aegilops tnticoides polli-
nated with pollen of wheat, and giving as a result Aegilops spel-
taeformis, which, he says "at first fertile to a mediocre degree,
like all hybrids of the second generation, produces, in the follow-
ing years, as many seeds as any Aegilops or Triticum known,
(p. 272.) The fact that the fecundity of the hybrids does not
always bear a relation to the facility with which the cross is
effected in the first place, is illustrated by Godron from Verbas-
cum crosses, especially Verbascum austriaco-nigrum X phoem-
ceum. (p. 283.) This sterility he recognizes as being due to one
or several possible operating causes : The complete absence of
pollen, defective pollen — deformed, etc. — or physiological steril-
ity, as in the case of Antirrhinum majus, A Barrelieri^ which, al-
though having an abundance of pollen, apparently completely
normal, yet remained entirely infertile.

Godron again comments on the very great vegetative develop-
ment in hybrids of Verbascum :

"The numerous branches, and the immense quantity of flowers which
arise on these branches, would they not exhaust the vegetable juices at
the expense of the organs of reproduction ^" (p. 287.)

With regard to the question (p. 289) whether hybrids, self-
fertilized, sometimes retain their characters unchanged for sev-
eral generations, and thus become the type of constant races, or
whether, on the contrary, they always return to the forms of
one of their parents after several generations, Godron gives his
case of Linaria hybrids, stating that :

"these hybrid forms may become very fertile, and a certain number of
individuals return, after the second generation, to the one and the other

PLANT HYBRIDIZATION BEFORE MENDEL 129

of their two primitive types, when they grow in company with their
parents ; and that this return movement manifests itself still more in
the succeeding generations." (p. 289.)

He notes that the same fact was observed by Lecoq in fertile
hybrids of Mirabilis, by Naudin in fertile hybrids of Nicotiana^
and by himself in hybrids of Petunia vioLacea X nyctaginae'
flora.

"These facts," he says, "seem to militate in favor of this opinion, that
hybrids are not able, contrary to the opinion of Linnaeus, to form new
permanent types, or, in a word, new species." (p. 290.)

He then cites at full length the exception already noted, of

A egilops speltaeformis :

". . . which seems to constitute a permanent hybrid race, and appears
to comport itself like a veritable species." (p. 290.)

However, after a careful review of the results of his own ex-
periments with Aegilops and those of Fabre, he decided that
Aegilops speltaeformis does not behave like a true species, even
though it is fertile, that its propagation and permanence remain
dependent upon the care of man, and that, abandoned to itself,
it is destined to perish. Hence, Godron concludes (p. 296.) :

"Hybridity remains thus no less one of the most precious means of
recognizing what is a species, and of distinguishing it from that which

IS not."

Nothing could show more clearly than Godron's small memoir
of 1862 the point of view of his time regarding the hybrid ques-
tion. Hybrids in many cases, well experimented upon, were seen
to "return" gradually to the parental types. In what manner or
to what degree, statistically speaking, such "reversion" occurred,
was not made the subject of inquiry. Infertility of hybrids of
"true species," or fertility of crosses of "varieties," was a deter-
mined fact, accepted as relatively certain, and valued as a sort
of criterion or means of ascertaining what organisms were "spe-
cies," and what were "varieties."

Naudin.

With regard to the paper of Naudin (4c), the general conclu-
sions of importance for his time, at which he arrived, are as
follows, in the language of the Committee of Award of the
Academy, which is quoted verbatim to show the point of view in
the science then prevailing :

130 PLANT HYBRIDIZATION BEFORE MENDEL

"The first and the most important of all is that the singular beings
which result from the cross-fertilization of two different types, far from
being condemned to absolute sterility, are frequently endowed with the
faculty of producing seeds capable of germination." (i, p. 129.)

An essential feature in Naudin's paper, of high importance
from our present standpoint, is the independent behavior of
characters in a cross, referred to by the Academy committee as
follows :

"Not content with responding by numerous experiments to the ques-
tions propounded by the Academy, the author . . . has sought to throw
light upon several points, some obscure, others not yet studied, in the
history of hybrids. He has confirmed that which Sageret already knew,
that in a hybrid the characters of the two parents are often shown,
not blended but approximated, in such fashion that the fruit of a
Datura hybrid, born of two species, the one with a smooth, and the other
with a spiny capsule, presents smooth surfaces in the midst of a surface
generally spiny. This 'disjunction,' as it is called, is explained according
to him by the presence in the hybrid of two specific essences, which tend
to be separated more or less rapidly the one from the other. He even
sees in this disjunction the true cause of the return of fertile hybrids
to the specific types from which they came." {ib., p. 131.)

It is further of great interest to note that the seeds gathered
from the smooth side of the capsule reproduced only the smooth-
capsule form, Datura laevis, while those taken from the spiny
side gave rise only to the spiny form, Datura stramonium. In Ver-
lot's paper, yet to be discussed, further instances of this type of
segregation will be found.

Naudin stated more clearly and definitely than others had
hitherto done the fact of the general uniformity of the hybrid
offspring of the first generation, and the diversity of form, with
partial reversion to, or, as we would now put it, the reappearance
of, the parental types, in the second hybrid or F2 generation. His
language is as follows :

"Finally, one may say that the hybrids of the same cross resemble one
another in the first generation as much, or almost as much, as the indi-
viduals which come from a single legitimate species." (4c, p. 188; Comp-
tes Rendus, 4d, p. 839.)

In contradiction to the results derived by Sageret from his par-
ticular set of experiments, Naudin asserts the generally inter-
mediate nature of the first generation hybrid condition :

"All the hybridologists are in accord in recognizing that the hybrids
(and it is always a question of the hybrids of the first generation) are
mixed forms, intermediate between those of the two parent species. This
is, in fact, what takes place in the immense majority of cases; but it

PLANT HYBRIDIZATION BEFORE MENDEL 131

does not follow therefrom that these intermediate forms are always at
an equal distance from those of the two species." (4c, p. 189.)

He goes on to remark upon the vagueness with which this rela-
tive approximation is determined, resting as it does largely upon
a basis of opinion. He also calls attention to the fact, that some-
times hybrids resemble one of the two parents in certain parts,
and the other in other parts.

Regarding segregation in the second hybrid generation, he
says :

"Very often, to the so perfect uniformity of the first generation, there
succeeds an extreme medley of forms, some approaching the specific
type of the father, the others that of the mother. . . . (4c, p. 190.)

"it is, as a matter of fact, in the second generation that this dissolution
of the hybrid forms commences in the great majority of cases. . . . (4c,
p. 190.)

"Among several of these hybrids of the second generation, there is
a complete return to one or the other of the two parental species, or to
both, and diverse degrees of approach to these species." (4c, p. 191.)

Naudin now comes to what he regards as the philosophical ex-
planation of these facts.

"All these facts are naturally explained by the disjunction of the two
specific essences, in the pollen and in the ovules of the hybrid. A hybrid
plant is an individual in vjhich are found united two different essences,
having their respective modes of development and final direction, which
mutually counter one another, and which are incessantly in a struggle
to disengage themselves from one another!' (4c, p. 191.)

The above is Naudin's statement of the "law of disjunction."
It is essentially a statement of the principle operating in what is
known as Mendel's Law, but must be regarded rather as a philo-
sophical inference, or divination of the truth, than as a scientific
conclusion derived from the data of specific experiment.

"The hybrid," says Naudin, "in this hypothesis, would be a living
mosaic, in which the eye would not discern the discordant elements as
long as they remained intermingled ; but if, in consequence of their
affinities, the elements of the same species, mutually approximating one
another, agglomerate in rather considerable masses, there may result
therefrom parts discernible to the eye, sometimes entire organs, .etc."
(4c, p. 192.)

Naudin concludes that the pollen and the ovules, and the pollen
especially, "are the parts of the plant where the specific disjunc-
tion takes place with the most energy." f4c, p. 193.)

He goes on to suppose (and here, perhaps, he comes close to a
statement of Mendel's view), viz.:

132 PLANT HYBRIDIZATION BEFORE MENDEL

"That, in the hybrids of the first generation, the disjunction takes
place at the same time in the anther and in the contents of the
ovary; that some of the grains of pollen belong totally to the species
of the father, and others to the species of the mother; that in others
again the disjunction has not occurred or has just commenced : let
us grant again that the ovules are, in the same degree, segregated
toward the side of the father and toward the side of the mother. . . .
If the tube from a grain of pollen approximated to the species of the
male parent encounters an ovule segregated in the same direction, there
will be produced a plant entirely reverted to the paternal species. The
same combination being accomplished between a grain of pollen and
an ovule, both separated in the direction of the female parent of the
hybrid, the product will return in the same way to the species of the
latter; if, on the contrary, the combination is effected between an ovule,
and a grain of pollen, segregated in a direction contrary the one to the
other, there will result a true cross-fertilization, like that which has
given birth to the hybrid itself, and there will result therefrom a form
intermediate between the two specific types." (4c, p. 193.)

In 1864, Naudin communicated a second report to the Academy,
in which he confirmed his previous results as to uniformity in the
first generation crosses, the identity of reciprocal crosses, and the
"disorderly variation," as he calls it, of the hybrids of the second
and succeeding generations. In neither of the two papers is there
any numerical classification of the hybrid types.

Naudin's memoir is often referred to as amounting virtually
to a statement of Mendel's law of the disjunction of hybrids. In
Naudin's case, however, the statement was of a speculative na-
ture, and consisted in the propounding of a scientific hypothesis ;
in Mendel's case, his "law" was a scientific conclusion derived
as the result of experiment.

Reviewing this list of statements in the light of present knowl-
edge, we can see that they constitute a more or less correct, non-
scientific formulation of the truth.

For example, the more or less rapid return of hybrids, that is
to say of heteroz3^gotes, to the parental forms, is a now suffi-
ciently well-established fact of segregation according to Men-
delian ratios, which, if there be a single pair of allelomorphs in
question, takes place on a 1:2:1 basis in each successive self-
fertilized generation. The more or less rapid return to its parents
of the hybrid fertilized by its parent, means, of course, the split-
ting of 50 per cent dominants, or recessives, as the case may be,
which are like the parental types in the case in question.

Naudin propounded, in 1863, a well-reasoned theory of prob-

PLANT HYBRIDIZATION BEFORE MENDEL 133

able truth; Mendel, however, in 18^, formulated a statement of
ascertained fact.

In 1865, Naudin, who had won so much credit for his memoir
on hybridization in 1863, published a paper on what he termed
"disordered variation" in hybrid plants, occurring as the result
of crosses he had made between a variety of cultivated lettuce
and a wild species [Lactuca virosa). Of the cross he says:

"The hybrid of the first generation was very fertile, and from the
seeds sprang a multitude of young plants, very varied in aspect, which
intermingled in all degrees the characters of the two species."

Of these Fo plants, twenty were preserved, concerning which he
remarks that they presented as a whole "all the phenomena of
the most disordered variation."

No two individuals of the twenty in the second generation were
alike, and yet, so far as the characters were concerned, nothing
new was seen to appear that had not already existed in the one
or the other parent.

"One essential point to bring forward here," Naudin adds, "is that,
in this overlapping of the characters of the two different species, one
does not see anything new appear, anything which does not appertain
to the one or to the other. Variation, as disorderly as it may be, moves
between limits which it does not transgress. The two specific natures
are engaged in a struggle in the hybrid, to which each one brings its
contingent ; but from this conflict there do not really issue new forms ;
that which is produced is never but an amalgamation of forms al-
ready existing in the parent types. The hybrid is but a composition of
borrowed pieces, a sort of living mosaic, of which each piece, discernible
or not, is ascribable to one or the other of the producing species."

Naudin concludes that not the surrounding medium, but the
nature of the ancestry, is the cause of all the variations seen in
plants. He calls attention to the fact that seeds of the same sow-
ing, although exposed to the sam.e environment, do not vary in
the same manner.

"We see the variation without any rule, by the sowing of their seeds,
of plants subjected since time immemorial to our cultivation, such for
example as the vine and the greater number of our fruit trees ; it all
brings us to think that they owe it to crosses, probably very ancient
and possibly anterior to all domestication, between neighboring species."

Naudin then answers the question, "Whence comes heredity
and what is it," as follows :

"it is always the passage from one equilibrium to the other, and al-
ways along the line of least resistance."

134 PLANT HYBRIDIZATION BEFORE MENDEL

The term "disordered variation" (variation desordonnee) is
probably employed by Naudin for the first time in his paper of
November 21, 1864, "De I'hybridite consideree comme cause de
variabilite dans les vegetaux." (4d, p. 157.) The use of the term
arose from experiments in crossing, reciprocally, Datura laevis
and ferox. In 1863, sixty individuals were grown of the cross
laevis X ferox, and seventy of ferox X laevis. Of these plants,
all of which came to full development, he says,

". . . they have been so perfectly like one another that the two lots
would have been easily taken for a single one." (p. 155.)

This result he considers a new confirmation of the conclusion
already announced in his memoir presented to the Academy in
1863, (4c) :

". . . that there is no sensible difference between the reciprocal hy-
brids of two species, and that in the first generation the hybrids of the
same derivation resemble one another as much as do the individuals of
the same pure species, issuing from the same sowing." (4d, p. 155.)

"In this first generation," he adds, "the entire collection of the hybrid
individuals of the same origin, however numerous they may be, is as
homogeneous and as uniform as a group of individuals would be of an
invariable species, or of a pure and clearly characterized race." {ib.^

P- 155.)

According to Naudin's statement, although both the parents
had white flowers and green stems, the hybrids of the first gen-
eration were all characterized by violet flowers and brown stems,
and with spiny fruits. This development Naudin ascribes to an
extension, over the whole plant of the hybrid, of a character
which was found to appear in a rudimentary way in the stems
of the seedlings of D. ferox, which, at the time of germination,
are stated to be of a deep violet-purple, extending from the root
to the cotyledons, where it suddenly stops, giving way to a clear
green tint. In the hybrids of the first generation :

". . . it takes on an enormous increase, reaching all parts of the plant,
and manifesting its action especially upon the flower." (p. 156.)

In 1864 the second generation of plants of the two reciprocals
was grown. Nineteen plants were raised of D. ferox X l^e'vis,
and twenty-six of D. laevis X ferox.

"To the great uniformity [i.e., of the first generation! there succeeded
the most astonishing diversity of forms, a diversity which is such that,
of the forty-five plants which compose the two lots, one would not find
two which exactly resembled each other." (p. 157.)

PLANT HYBRIDIZATION BEFORE MENDEL 135

The plants differed from one another in height, habit, form of
the foliage, coloration of the stems and flowers, degree of fer-
tility, size of the fruits and their degree of spinescence. The
various vegetative characters are given in a descriptive man-
ner and in some detail, but without classification.

"To sum up," he says, "the forty-five plants of the two lots, consti-
tute, so to speak, as many individual varieties as if, the bond which
attached them to the specific types being broken, their vegetation had
wandered in all directions. This it is that I call 'disordered variation'
[variation desordonnee], in opposition to another very different manner
of varying of which I shall speak farther on." (p. 157.)

The idea seems not to have suggested itself to Naudin that
there could necessarily be any ascertainable law underlying the
confusion which the variations in question represented, or that
any quantitative study of the characters of the plants of the
second generation was therefore necessary.

In an article, "Sur les plantes hybrides," published in the
Revue Horticole for 1861, Naudin had already arrived from his
experiments at certain conclusions regarding the hybrid condi-
tion. The hybrid, he says (4b, p. 397), may have characters of
two orders : The first, to which in general the most attention is
given, is the mixture in diverse proportions of the characters
peculiar to each of the parental forms, and which constitutes the
hybrid a form intermediate between the two. This mixture of
characters may be an equal distribution of the characters of the
two parents, but more often it is very unequal, in which case the
hybrid more or less sensibly approaches one of the two species.
In general, this fusion of characters is seen in all the parts of
the hybrid, but there are cases, more rare, as Naudin states :

". . . where the characters dissociate [se dissocient] to occupy sepa-
rately and exclusively certain organs, so that the hybrid appears to be
formed of heterogeneous parts, borrowed from the two species, and as
it were, soldered to one another." (p. 397.)

The hybrid orange, in which the fruit is lemon in certain por-
tions and orange in others, is cited as "one of the best known
examples of this form of disjunctive hybridity."

Often the two orders of characters exist simultaneously in
the same hybrid plant, but is it not rare, says Naudin, for one
of them to appear alone.

"it is a rare case where a hybrid resembles exclusively one of the two

136 PLANT HYBRIDIZATION BEFORE MENDEL

parents ; that is to say reproduces identically one of the two specific
forms." (p. 397.)

In the same article Naudin reports upon an experiment in
crossing Petunia nyctaginaeflora, with white corolla and yellow-
ish pollen, by Petunia violacea, with purple corolla and violet-
blue pollen. Naudin says :

"Our experiments have taught us that the hybrids in the first genera-
tion are very uniform in most of the species." (p. 398.)

Of thirty-six plants derived from the above cross, thirty-five
were very much alike, with lilac flowers and bluish pollen. The
second generation is recorded in some detail. Ten plants resem-
bled P. vwlacea in form and color, so that it was impossible to
distinguish them from the type. Nineteen plants had flowers
white or very feebly rose-colored, with violet throat and with
grey-blue pollen. Sixteen plants had flowers more or less lilac.
One only had white flowers. In the third generation 1 16 plants
were grown (in 1856), concerning which it is not necessary to go
into detail.

The conclusion which Naudin drew from his Petunia experi-
ments, repeated, as he says, several times, was to the effect that
at least in the genus in question :

". . . the hybrids have no constancy, and that one is not able to
count upon the sowing of their seeds to reproduce and preserve the
varieties which crossing has caused to arise." (p. 398.)

19. Verio fs Memoir on the Breeding of Plants.

In 1865, B. Verlot of the Jardin des Plantes at Paris published
a brief memoir, which in 1862 had received a prize from the
Imperial and Central Horticultural Society, the thesis of which
was as follows :

"To demonstrate the circumstances which determine the production
and fixation of varieties in ornamental plants."

The memoir is of interest as thoroughly and typically em-
bodying the general point of view of the day concerning hybrid-
ization and the origin of new varieties, while affording at the
same time much matter of interest from the standpoint of prac-
tical horticulture.

Verlot presented the view that, while the causes of variation
are unknown, they arise under definable circumstances, chief

PLANT HYBRIDIZATION BEFORE MENDEL 137

among which he enumerates prolonged cultivation, removal from
one set of climatic and soil conditions to another, and hybridiza-
tion.

The thought of the time did not clearly distinguish a differ-
ence between the nature of the changes brought about by the
external environment, and those arising from sexual fertiliza-
tion. Both were generally assumed to be equally heritable. Culti-
vation long continued was considered to have been especially
potent in bringing about variation. In Verlot's words :

"it is especially with plants cultivated for a great number of years,
with those the introduction of which is so ancient that it is lost in the
night of time, that one finds profound and multiplied modifications."
(6, p. 4.)

He further voices the then prevailing view regarding the rela-
tion between culture and variations :

"if we compare," he says, "a species in its spontaneous condition with
the same species cultivated, transported, that is to say, most often into
conditions of climate, soil, etc., completely different from those in which
it lived before, we shall be struck by seeing that, in our gardens, this
latter will show derivations of type more numerous than in the wild
state. We shall infer from this fact the consequence that the faculty of
varying, which is proper to the plant, augments with culture, if we
observe then that the plants cultivated in our gardens which have varied
the most, as for example the dahlias, the roses, the camellias, the rhodo-
dendrons, the potato, etc., are not borrowed for the most part from our
flora, nor from one of the neighboring floras, but on the contrary come
from distant countries, where they grow under conditions often abso-
lutely different from those in which we cultivate them, we shall con-
clude that, the more a species is depatriated, the more easily it will
vary." (6, p. 30.) And again, "the more plants are cultivated, the greater
their variations are and, by the same token, the easier they are to fix.
We will possibly be contradicted, but we do not hesitate to consider,
once more, long practised culture as one of the most favorable antece-
dents to the rapid fixation of variations," (6, p. 38.)

It now seems probable that the increased variation manifested
by wild plants, when brought into cultivation, is due to the re-
moval of the restrictive influences of competition, rather than
to any actual increase in the range of heritable variability itself.

Verlot cites, as examples of the changes supposedly wrought
by culture, the changes brought about in the roots of such plants
as beet and parsnip ; in the production of dwarf plants ; in vari-
ous modifications of general habit, such as fastigiate, pyramidal
and weeping variations in trees ; in the appearance of variations
with laciniate or otherwise modified leaves ; in the varieties with

138 PLANT HYBRIDIZATION BEFORE MENDEL

leaves colored white, yellow, red, or brown; in the arrangement
of the leaves, as in the sudden appearance, on an ordinary alter-
nate-leaved plant of Rosa alba, of a shoot with opposite leaves,
propagated as Rosa cannabifolia. From the evidence he concludes
that cultivation sets up within the plant a condition of instability,
which gives rise not only to seed variation, but to variation within
the plant itself — what we would call bud-variation or "somatic
segregation," as in the case just cited; the case of a chrysanthe-
mum reported, which bore at the same time yellow- and rose-
colored flowers; and of a citrus fruit half-and-half orange and
lemon. Another case cited by Verlot is that of a variegated
Camellia imperialis, which for twelve years had constantly given
brilliant white flowers set off with rose-colored striations and
variegations, and upon which a small branch appeared one year,
bearing three flowers in a group, of a uniform color, the same
tint as that of the striations and variegations of the other flowers.

"It is evident in these cases," says Verlot, "that the colorations dis-
join, and that this variation returns by disjunction to its colored parent
for certain plants of hybrid origin." (6, p. 67.)

"As we see," he says, "by the sole fact that a plant is cultivated it is
forced to vary. The instability of a cultivated plant is even evident in
certain cases, in such a way that it does not only manifest itself in the
direct descendants of the plant, but also in the plant itself. Thus, while
the generality of the branches of a plant bear leaves, flowers and fruits
of definite forms or colors, a branch is sometimes produced, in which
the leaves, flowers, and fruits present completely different characters.

"We recognize that culture has been, and is still, the essential cause
of the variation of plants, and that thereby man has, so to speak, com-
pelled them to re-clothe themselves with new forms appropriate to his
needs or to his caprices." (6, p. 5.)

The above statement excellently presents the older point of
view regarding variation. Such cases as the rose, chrysanthemum
and orange, and the famous chimaera, Cytisus adami (C. pur-
pureus X Laburnum), Verlot accounts for under the guise of
Naudin's conception of "disjunction."

"It Is by disjunction that, in these last cases, the specific forms thus
appear in hybrid plants, and it is with woody plants, it will be noticed,
that this fact achieves all the phases of existence of a hybrid plant, an
existence of which this disjunction would be the last term." (6, p. 14.)

He then refers to Naudin's case of disjunction in Datura, which
is elsewhere discussed.

Verlot's expression of view on the matter of methods of selec-

PLANT HYBRIDIZATION BEFORE MENDEL 139

tion is so thoroughly typical of the thought of his time, viz., that
variation is in consequence of the "breaking up" of the "type,"
and that selection ipso facto, intensifies the variation in the
direction selected for, that it is a matter of interest to present
here the view expressed.

"if a variation is produced in a direction other than that toward
which one tends, it ought not to be abandoned for that; one will have
more chance to obtain new variations in sowing a deviation from the
type, even in a diametrically opposite direction, than in sowing anew
the type itself. In the deviation there is already a tendency toward
perturbation, and toward the beginning of the destruction of atavism."
(6, p. 31-)

Another interesting example of the older point of view regard-
ing plant improvement is Vilmorin's opinion, quoted by Verlot,
which is here reproduced to show how thoroughly the primary
idea concerning the "breaking up of the type" in order to bring
about "variation" entered into the thought and operations of
pre-Mendelian breeders.

"To obtain from a plant not yet modified varieties of a kind deter-
mined in advance, I will first set myself to making it vary in some
direction or other, choosing for the reproducing factor, not that one of
the accidental varieties which would most nearly approach the form
which I have proposed to myself to obtain, but simply that which
would most differ from the type. In the second generation, the same
care would make me choose a deviation, the greatest possible at first,
the one most different, in a word, from that which I would have chosen
in the first place. Following this direction for several generations, there
necessarily ought to result, in the products obtained, an extreme ten-
dency to vary; there then results again, and that is the principal point
according to me, that the force of atavism, asserting itself counter to
very divergent influences, will have lost a great part of its power, or,
if one ventures to make use of this comparison, it will exert it always
in a broken line." (6, p. 28.)

Man's relation to the fixation of characters in new races of
plants is stated by Verlot in the usual manner prevalent in the
days before Mendelian analysis :

"In brief, gardeners have remarked, ^with reason, that a plant newly
introduced is very susceptible to vary. This fact, it is conceived, has
nothing surprising about it. It confirms that which we have previously
said, that a variety, whatever it might be, had need, in order to become
fixed, of being cultivated for a greater or less length of time, until one
had finally come to maintain with it the tendency not to depart from
being that which he had made it." (6, p. 70.)

In other words, the idea then prevalent and more or less im-
perfectly expressed was that, in some unknown manner, man, by

140 PLANT HYBRIDIZATION BEFORE MENDEL

continued selection, succeeds in impressing upon a "variety" the
stamp of a certain type and, through repeated and continuous
selection in the same direction, finally "fixes" it, so that the
variety becomes, as it were, stabilized.

It probably usually means that, by continuous selection of
some certain type, those individuals are usually isolated, which
are more or less homozygous for the character-units thus repre-
sented, and which become "fixed" because no heterozygous fac-
tors are left to split apart.

We have here, in other words, an unscientific expression,
through practical experience, of the fact which the breeder of
today would define as the selection of a heterozygote having
dominant characters differing from those of the species. Being
of hybrid nature, such a plant would break up, and hence yield
to selection, whereas the plants resembling the type, being more
apt to be homozygous, would be less liable to vary in their prog-
eny. He emphasizes the view just set forth still more emphati-
cally in the following words :

"if two variations are produced, of which the one differs little from
the type, but is placed upon the line which leads in the desired direction,
and the other is placed in an opposite direction, but departing consider-
ably from the type, we shall not neglect nevertheless to follow this
latter, because with it the breaking-up of atavism is more advanced."
(6, p. 31-)

The necessity of fixing upon some single individual plant, as the
basis of selection, is referred to by Verlot in the following terms :

"We ought then to recognize that it is necessary to take account for
the choice of the seed-bearers, not only of the external characters, but
even of the idiosyncrasy of each one of them. Now, since this does not
manifest itself except by its effects, we shall, if a variation seems to
present some difficulties in becoming fixed, have to examine separately
the products of each of the seed parents, and make our choice bear upon
those which present, in the least pronounced degree, atavism or the
tendency to return to the primitive type." (6, p. 32.)

Verlot's experience with and observations upon hybrid plants,
as coming from an experienced horticulturist, are valuable, espe-
cially to the practical plant breeder.

Regarding the now well-understood fact of the gradual disap-
pearance of the hybrid form through segregation, he says :

"Their fertility is of short duration, through the more or less rapid
return of their products to the types which have given them birth."
(6, p. 25.)

PLANT HYBRIDIZATION BEFORE MENDEL 141

Regarding the general aspects of plant hybrids, he adds :

"All their characters, of whatever nature they may be, with the ex-
ception of a more considerable development of the organs of vegetation,
are in general intermediate between those of the parents, but always
limited by them." (6, p. 25.) •

Regarding the matter of the bounds or limits of the hybrid

characters, he remarks elsewhere :

"Let us call attention to a circumstance always constant in the hybrids,
which we have to consider, that is the absence in the products of colors
other than those, or a combination of those, of the parents. We shall
insist upon this characteristic, because we shall have occasion to recur
to it; it will serve us to establish that, up to now, the facts prove that,
by hybrid fecundations, one will obtain, in whatever part of the plant
they present themselves, only the variations of color limited to those of
the parents." (6, p. 18.)

Since Verlot's view regarding the nature of a "hybrid" was
the conventional one, that it consists of a cross between what are
commonly called distinct "species," he was led to notice the very
common fact of comparative sterility in these cases. Noting the
well-known characteristic of augmented vegetative growth in
hybrids, he is led to ascribe the frequent seed-sterility to this
latter — a conclusion easily if naively arrived at, from the well-
known inverse relation between undue vegetative luxuriance and
seed reproduction. As an instance of intermediacy, Verlot alludes
to the matter of height :

"In crossing an almost dwarf species with the pollen of a taller
species, . . . the seeds of this cross will undoubtedly produce individ-
uals taller than was their mother." (6, p. 44.)

Regarding intermediateness in size in flowers, he says :

"In crossing a species 'parviflora by its variety 'grandiflora we shall
be able ... to obtain individuals with flowers larger than those of their
mother; by crossing, one is able then to create a race or a variety in
which the size of the flowers will be augmented." (6, p. 47.)

With regard to the same matter in respect to earliness and
lateness, he says :

"Supposing one crosses a very early plant with its very late variety,
or vice versa, one will only be able to obtain varieties intermediate
between the parents in earliness or lateness." (6, p. 50.)

Regarding fragrance, he mentions the case of a cross between
Rhododendron ciliatuin (odorless), and R. edgeworthii (very
fragrant), the hybrid being less intensely fragrant than the pol-
len parent. (6, p. 31.)

142 PLANT HYBRIDIZATION BEFORE MENDEL

In the matter of color intermediateness, he makes the state-
ment :

"Once obtained, white coloration is able to serve, either by crossing
or by hybridization, in the production of new variations ordinarily in-
termediate between them and the color from which it has proceeded."
{ib., p. 59.)

In other words, presumably, dilution through the presence of
but a single dose of the color factor.

The most interesting portion of Verlot's memoir is his discus-
sion of the practical results achieved with ornamental plants in
the field of hybridization.

Regarding dwarfing, he cites McNab (p. 42) to the effect that
the best dwarf varieties of Rhododendron are obtained by the use
of pollen taken from the small stamens :

". . . the products of which," he says, "I am able to certify, are very
different from those obtained by the use of the pollen of the large
stamens."

Regarding breeding for winter-hardiness, he mentions the case
of the cross of Amaryllis brasiliensis^ a delicate species impossible
to winter out of doors, by Amaryllis vittata, a much hardier
plant, whereby hybrids were produced which, with light cover-
ing, would withstand the climate of Paris. Likewise, Rhododen-
dron arhoreum^ which cannot resist more than two to three degrees
of cold, gave, when crossed by R. catawhiense — a much hardier
form, though with inferior inflorescence — hybrids which inherited
the hardiness of the female parent.

Verlot did not recognize the phenomenon of dominance as such
in the first generation of the hybrids, but he mentions the case
of a white Gloxinia^ crossed by pollen from a blue-flowered
variety, in which, out of one thousand seedlings,

". . . all bore nothing but perfectly blue flowers, not a single one of
them being white nor a single one variegated." (6, p. 65.)

Regarding the inheritance of variegations, it may be of interest
to note that the following species are mentioned, in which the
variegated form breeds true from the seeds.

Alyssum maritimum Celtis australis

Bar bare a vulgaris Cheiranthus cheiri

With these are to be included the variegated ferns Pteris ar-
gyraea and P. aspericaulis var. tricolor.

PLANT HYBRIDIZATION BEFORE MENDEL 143

He remarks upon an interesting fact, that the variegations do
not appear upon the first leaves of a variegated variety.

Regarding the heredity of double flowers, he reports no cross-
ings, but simply remarks upon cases of double-flowered peach
and apple, which came true from the seed. (6, p. 83.)

Verlot summarizes his views upon hybrids in the following
words, which are worth reproducing because they fairly well rep-
resent the general knowledge of the time as follows :

(1) "Hybrid fecundation is not able to produce anything but variations
which will be able, it is true, to multiply themselves mechanically,
but which will not be fixable, and which consequently cannot be
brought to constitute races or varieties, the fertility being limited to
a few generations, or disappearing, after a certain time, by the dis-
junction of the types.

(2) "One of the characters of the hybrids is also a great development
of the vegetative organs, coincident with less abundant flowering.
They are in general intermediate between the species types, but
often approach more the father.

(3) "The hybrid, fertilized by a parent, returns also promptly to the
parent.

(4) "The hybrid, self-fertilized, returns more or less rapidly to the
parents.

(5) "Crossing, that is to say, reciprocal fertilization of varieties of races
of the same species, will serve for obtaining new variations, inter-
mediate between the parents, very fertile, and which can be fixed
more or less rapidly and constitute new varieties or races." (6.)

20. The Work of the Vilmonns.

The eminent services of the Vilmorin family for over two hun-
dred and thirty years to French agriculture, and particularly
through the improvement of the sugar-beet and of wheat, cannot
be taken up here. It would not, however, do justice to the mental
activities of a long succession of the members of this family, and
of the distinguished house of Vilmorin-Andrieux & Cie. of Paris,
if one omitted to at least mention the fact that, through no less
than seven generations of father and son of the family of
Vilmorin, there were published by them, in journals and annals
of agriculture and horticulture, in proceedings of agricultural and
horticultural societies, and in journals of botany and related sub-
jects, more than three hundred and sixty articles dealing with
plants, from the various standpoints of agriculture, of horticul-
ture and floriculture, and of botany. Some fourteen of these were
contributed to the Bulletin de la Societe Botanique de France. It

144 PLANT HYBRIDIZATION BEFORE MENDEL

remains in the present instance to discuss the contributions of
Louis de Vilmorin (1816-1860), and of his son Henry (1843-
1899), to investigations in heredity and in hybridization.

The first experimental effort, since the work of Sageret, to find
a definite numerical relation in the transmission of characters
from a cross was the work of Louis de Vilmorin, carried on with
Lupinus hirsutus from 1856-1860, and reported upon by his son
in 1879. (7b.) This species affords the advantage of being gen-
erally self-fertilized, and has ordinarily blue, but also frequently
rose-colored flowers, there being no other color or intermediate
shade. The plants used came from seeds of these two varieties,
from commercial lots, kept pure by rogueing out all plants not of
the desired color. It was Vilmorin's conception that, in a self-
fertilized plant such as lupine, there was introduced a great ad-
vantage in the study of heredity, since each individual was the
descendant of a single plant of the preceding generation, and not
of a number of ancestors, doubling itself at each stage, as in the
case of plants where two individuals are involved in seed re-
production.

"It may then be admitted," says Vilmorin, "that the seed sowed the
first year of the experiments, in 1856, reckoned a series of at least fifteen
ascendants, which have given flowers constantly of the same color, blue
for some, rose for the others." (7b, p. 6.)

No crosses were made, but records were kept for four years of
the different kinds of plants derived from each sowing. Out of the
progeny produced each year, instead of planting all or a consid-
erable number, but one representative of each color was planted,
as a rule, so that large numbers are not available. The fact that
both the blue and the rose-colored plants for the most part broke
up into blue and rose for each year indicates that each strain was in
the hybrid or heterozygous condition.

In forty cases during the five years, the rose-flowered plants
broke up into blue and rose ; in three apparently, and in the other
cases possibly, there appeared to be a 3 : 1 ratio of rose to blue.
In thirty-six cases in the same period, the blue-flowered plants in
turn broke up into blue and rose ; in six of these cases, the ratio
was close to 3: 1. It is evident that Vilmorin's experiments need
repetition, since a clear breaking-up of both blue and rose-flowered
plants into blue and rose again would not be expected. A few
cases of rose and a few cases of blue bred true. To V^ilmorin, it

PLANT HYBRIDIZATION BEFORE MENDEL 145

was simply a question of filtering out the progeny until they be-
come true, either rose or blue-flowered. He remarks upon the fact
that "the color blue persists more obstinately, becomes fixed more
quickly, and once fixed maintains itself better, than the rose
color." (7b, p. 8.)

Plate XXVIII. Louis Leveque de Vilmorin, 1816-1860.

146 PLANT HYBRIDIZATION BEFORE MENDEL

This experiment is one of the few attempts at obtaining infor-
mation as to the numerical relations between the progeny of plants
in the hybrid condition, although in the present instance, the
plants not having been knowingly crossed, they were not regarded
by Vilmorin as being in the hybrid condition with respect to
flower color. The fact of their breaking-up, however, shows that

Plate XXIX. Henry Leveque de Vilmorin, 1843-1899.

such was nevertheless the case. This being true, it is probable that
the large number of irregular ratios which were obtained was due
to crossing by insects. Vilmorin was naturally unable to deduce
any precise conclusion from such an array of data. It must be

PLANT HYBRIDIZATION BEFORE MENDEL 147

kept clearly in mind that, from his point of view, a plant was
a constant struggle between two opposing forces, the force exerted
by its immediate parentage and that exerted by its ancestry.

"The characters of an individual plant are the result of the action of
two distinct, and in a certain measure, opposed forces. The first repre-
sents the tendency to individual variation or idiosyncrasy. It causes the
individual to present characters different from those of its ancestors,
while remaining enclosed within the limits assigned to the species. This
force, although probably complex in its nature as in its effects, may,
for facility of reasoning, be considered as 'simple.' The other force is
that which calls upon the individual to reproduce the character of its
ascendants." (7b, p. 41 ; 8, pp. 33-4.)

"This latter, simple, and insofar as the ancestors are concerned, of
the individuals which one considers have presented invariable charac-
ters, becomes on the contrary evidently complex, if there have already
been some variations. The tendency to assemble a collection of beings
dissimilar among themselves cannot be the effect of a single force, but
the resultant of several more or less divergent forces. One may call
'atavism' the tendency which, in this case, calls the plant to resemble
the totality of ascendants, and 'heredity' that which leads it to reproduce
the characters of the individual from which it immediately descends."
(7b, p. 4.)

In another place (yd), Henry de Vilmorin quotes his father's
viewpoint again as follows :

"if we consider a seed at the mornent when, put into the ground, it
gives birth to a new individual, we may regard it as solicited, so far as
the characters are concerned which the plant must exhibit to which it
is to give birth, by two distinct and opposing forces. These two forces,
which act oppositely, and from the equilibrium of which results the
fixity of species, may be considered as follows :

"The first, or centripetal force, is the result of the law of the re-
semblance of children to fathers, or atavism. Its operation has for its
results the maintaining, within the limits of variation assigned to the
species, of the departures produced by the opposite force.

"The other is the centrifugal force, resultant of the law of differences
in individuals or idiosyncrasy, and causes each one of the individuals
composing a species, whether one is able to consider it as the progeny
of a single individual or of a pair, to present differences which consti-
tute its own physiognomy, and produce that infinite variety in unity
which characterizes the works of the Creator." (p. 489.)

Vilmorin thought that the action, of these diverse tendencies
would be measured by the proportion of plants with blue flowers,
and of plants with rose-colored flowers, respectively, which pro-
ceed from the seeds of an individual of one of these two colors,
and especially since, in his view, there were no intermediates. The
inferences, rather than conclusions, which Vilmorin believes he is
able to derive from the experiment, are based upon the fact that

148 PLANT HYBRIDIZATION BEFORE MENDEL

the majority of the descendants, in his experiments, resembled
their immediate parent, and that the power of that which he calls
"direct heredity" is altogether preponderant. From the fact that
now and again a plant would "take back" to a more remote an-
cestor, he concluded that "atavism" was also a constant and ten-
acious force to be reckoned with.

"It is this force," he observes, "which causes to reappear the characters
of the great mass of the ancestors among distant descendants, across
numerous generations presenting different characters. The action of this
force may appear limited, if one considers only its influence upon a
single generation, but, if one reflects that it acts constantly and always
in the same direction, it is explained that it suffices to maintain the
fixity of plant species." (7b, p. 10.)

Elsewhere, Vilmorin further remarks regarding the forces in-
volved in inheritance :

"We come first, for the greater simplicity, to consider atavism as con-
stituting a single force, but, if one reflects, one will see that it presents
rather a bundle of forces acting almost in the same direction, and com-
posed of the individual call or attraction of all the ancestors. Now, to
facilitate the intelligence of action of this force, it will be necessary
for us to consider first, and in an abstract manner, the force of the re-
semblance to the mass of the ancestors, which may be considered as
due to the attraction of the type of the species, and to which we shall
reserve the name of atavism; then separately, and in a more special man-
ner the attraction of the force of resemblance to the father direct, or
heredity, which, less powerful but nearer, will tend to perpetuate in the
child the characters proper to the immediate parent."

Another conclusion which Vilmorin draws, is as to

". . . the very rapid enfeebling of the influence of heredity beyond
the first generation, in other terms, the little tendency which plants
show to resemble any ancestor exhibiting characters other than those
of the mass of ancestors, if this ancestor is not the immediate author of
the plants. We have seen frequent examples of blue plants issued from
two or three generations of rose plants, and giving birth nevertheless
to a progeny entirel}' or almost blue."

As to the conclusion which one may draw from these experi-
ments, he says :

"It will not be a mathematical evaluation of the comparative power
of the different forces which act upon the transmission of the characters
in the plants. On the other hand, in a word, one knows that the phe-
nomena in which the vital forces intervene do not permit themselves
to be reduced to figures, and on the other hand, were it otherwise, that
the number of individuals observed in each generation would not be
enough to give precise numbers, limited as that was by that of the seeds
of the hybrid plants, the seeds being in Lupinus hirsutus very large and
few."

PLANT HYBRIDIZATION BEFORE MENDEL 149

The only general conclusion which Mlmorin was able to derive
from the lupine experiment, which he was able to put into the
form of what. might be called "rules," are the following:

1. "a very marked tendency of plants to reproduce the characters of
the immediate ascendants ; it is the effect of direct heredity.

2. "A tendency less strong, but much more persistent, to resemble the
mass of the distant ancestors. It is that which has been spoken of under
the name of atavism.

3. "A rapid enfeebling of the tendency to reproduce the characters
of an ascendant which is not the immediate author of the plant, if these
characters are not those of the mass of the ancestors." (yd, p. 490.)

Vilmorin summarizes by saying :

"The experiment already gives indications which, approximated to
the results of the experiments made and to be made, will permit, one
day without a doubt, to be embraced in a complete and methodical
presentation the totality of the laws which regulate the heredity trans-
mission of characters in plants." (7b, p. 11.)

The difficulty with Vilmorin's experiment, as with so many
others before that of Mendel, was that it did not undertake to
deal with the progeny of plants purposely crossed with the object
of determining the numbers and proportions of individuals of the
different kinds., that appeared in the second and "variable" gen-
eration. So far as Vilmorin's experiment itself was concerned, had
the plants been covered, to prevent all pos^^ibility of crossing,
and had the numbers of the progeny planted been large, instead
of consisting of single representatives of the blue and rose-
colored strains, respectively, results of value to students of breed-
ing might have been definitely revealed.

In another memoir (8) Louis de Vilmorin raises the question
whether

". , , the qualities or the characters produced in an individual by ex-
ternal and accidental circumstances, such as are peculiar to it and have
not affected its ancestrv, are in some proportion transmissible sexually,"
(p. 2.)

Instinct, he says, leads him to a negative conclusion, although,
as he admitted, determinative data upon the subject were lacking.
In undertaking the study of heredity, Vilmorin remarks upon the
necessity of disengaging as much as possible the study of heredity
from the circumstances which might characterize its action. The
latter he finds complicated by the question of the range of the
variations in the plant induced by external conditions.

150 PLANT HYBRIDIZATION BEFORE MENDEL

"For it is only after having determined the normal amplitude of these
variations that one is able to judge if more considerable ones present
themselves, which one is able to attribute with certainty to the action
of the causes of perturbation which one studies." (8, p. 3.)

Vilmorin's scientific point of view is plainly shown in the fol-
lowing statement :

"The number of forces which are in play is so considerable, the man-
ner in which they are able to combine is so varied, that it explains to
me in part how difficult it is to obtain completely concordant results in
an experiment where all the influences, save that which one studies,
ought to remain invariable." (8, p. 4.)

In the following, Louis de ^'ilmorin shows an appreciation, in
advance of its scientific demonstration by Johannsen, of the prin-
ciple of using pure-bred strains or "pure lines" in breeding; of
breeding from the individual plant, and not by means of mass
selection. Referring to the breeding of the sugar beet, he says :

"All that I have been able to observe up to the present, on the question
of the transmission by heredity of characters in plants, makes me think
that it is necessary to individualize the observations as much as possible.
So I have adopted the custom, when I had to fashion a race, no matter
how little rebellious, of gathering and sowing the seed separately of
each one of the individuals which I have marked as my choice, instead
of making, as ordinarily, a choice composed of as many individuals as I
needed to collect the quantity of grain of which I had need, and I have
always remarked that among these individuals there were some which
always gave a better return than others, and which I finally adopted as
the sole type for amelioration." (8, p. 18.)

In 1890, Henry de Vilmorin reported (jd) an interesting obser-
vation with peas, similar in character to that of Goss, which
awakens surprise from its not having aroused further investiga-
tion. Speaking of the progeny, he says :

"All the seeds of the same plant are not rigorously alike among them-
selves. They differ, especially when the plant which has borne them
is of a mixed race, and has undergone, or is in the process of under-
going, modifications through the action of the environment in which it
ives.

Vilmorin then, in the following words, anticipated the present
point of view regarding the distribution of characters.

"The different characters which enter into the composition impress
themselves differently in the different seeds, and are reproduced in di-
verse combinations in the plants issuing from those seeds."

He proceeds to give as an illustration, precisely the case of the
distribution of characters which formed part of Mendel's experi-
ment.

PLANT HYBRIDIZATION BEFORE MENDEL 151

"It is known that among peas there exist races with white seeds, and
others which, even at maturity, have green seeds. Now this year [1889],
examining peas obtained by crossing a race with green seeds with a
race with white seeds, I have frequently found in the same pod seeds
of different colors. This character of color, easily appreciable to the eye,
permits the conclusion that all the seeds of the same plant are not
necessarily alike among themselves, nor endowed exactly with the same
faculty of reproduction." (p. 488.)

No analysis, however, was made of the nature of this phe-
nomenon, by growing separately the green and the white seeds
thus produced,

Vilmorin ventures no further view upon the fundamental na-
ture of hybridization than to say that cross-fecundation has this
inexplicable but well-determined result, so far as the characters
of the plant are concerned, "of grouping them in the different
seeds resulting from the cross in very variable combinations and
proportions."

It is to be seen that there exists here a recognition of the germ
of the idea of the segregation of characters, without, however,
furnishing the data for knowing their possible proportions.

Henry de Vilmorin reported to the Societe Botanique de France
(Sessions of February 27 and December 10, 1880; 7c, pp. 73-4,
356-61), upon the hybridization of wheat. "Several times in the
course of recent years," he states, "I have had occasion to make
crosses between different varieties of wheat, to the end of obtain-
ing new forms, presenting, from the agricultural point of view,
certain qualities which I sought to develop." (p. 73.) These crosses
originally made between varieties of Triticum sativum, suggested
the attempting of crosses also between different forms of wheat,
originally regarded as belonging to different species. The charac-
ters of the hybrids in the sativum crosses were reported as being
in general intermediate, now approaching one, now the other par-
ent, or offering characters found in neither. Crossing a pubescent
wheat, "Ble a duvet," reciprocally with a reddish, beardless, smooth
spelt {T. spelta), the products of the cross were intermediate
where spelt was the $ and "Ble a duvet" the $ parent. From the
reciprocal cross, eight similar and intermediate plants were ob-
tained. The grain was adherent to the glumes, and the rachis
fragile as in spelt, but less so. The important thing, in Vilmorin's
opinion, was the ability of two supposed "species" of wheat to

Plate XXX. Henri Lecoq.
mont-Ferrand.

Professor of the Natural Sciences at the University of Cler-

PLANT HYBRIDIZATION BEFORE MENDEL 153

cross, giving a uniform and strictly intermediate progeny. In the
more extensive report (7c, 356-61), reciprocal crosses made in
1878 were reported between T. sativum and T. turgidum, durum,
polonicum and spelta. All the possible combinations between sati-
vum and the other four were attempted with success, except in the
crosses upon T. polonicum $ . The reciprocals with this form as
$ succeeded. Crosses (reciprocally) with T. monococcum failed.
In the pubescent, white-chaffed, wheat-spelt crosses, the spelt char-
acters were reported as being the most strongly characterized in
the descendants. All combinations of color and pubescence of
glumes (except pubescence in the speltoid forms), is reported.
Second-generation results are given of crosses between "Chiddam
d'automne," a soft, white-chaffed, beardless wheat, by "Ismael," a
pubescent, hard wheat, and between "Ble Seigle," a red, pubescent,
beardless variety of T. sativum, and "Ble Buisson," a poulard
wheat. From the first-named cross, Vilmorin reports the second
generation in 1880 as giving the most diverse forms, no two alike,
nor a single one reproducing the characters of either of the original
parents. Not only were noted soft and hard wheats, but wheats
resembling poulard (T. turgidum), and more or less the spelts
(T. spelta), which, he remarks "is surprising in the progeny of a
soft and of a hard wheat." Of the cross with "de Beauce," the
second generation gave "the most curious mixture of wheats, dwarf
and tall as to straw, bearded and beardless, with heads extraordi-
narily slender or extrem.ely compact." (p. 359.) There also appeared
a form resembling T. durum, but beardless. The cross involving
"Ble Seigle" and "Ble Buisson" is reported as giving rise, in the sec-
ond generation, to "wheats of all sorts, bearded or beardless," but
among which "one notices a very marked tendency to approach
forms derived from T. spelta'' Among these there was "even a
branched spelt issued from two wheats with simple heads." These
cases appear to Vilmorin to be cases of the "disorderly variation"
reported by Naudin. He remarks, "Similarly to Naudin, it is in the
second generation that I observe this variation." (p. 359-) Vilmorin
further comments upon the appearance, among the progeny of the
two wheats, of characters not those of either of the parents, but
belonging to other wheat forms. The general conclusion is, "If

154 PLANT HYBRIDIZATION BEFORE MENDEL

these forms can be fixed with their present characters, it will be
very difficult to doubt that the most of the races of wheat, consid-
ered ordinarily as so many species, are in reality but variations of
one and the same plant." (p. 35'9-)

21. Lecoqs Memoir on Hybridization.

In 1827 appeared the first edition of a work by Henri Lecoq,
entitled "Recherches sur la Reproduction des Vegetaux." In 1845
appeared his work on hybridization, published in 1846 in German
translation. A second edition of the book was published as late as
1862. Lecoq, who was Professor of the Natural Sciences and Di-
rector of the Botanical Garden at Clermont-Ferrand, sought to
present the subject in such manner as would be of interest and
of tangible concrete value to the practical gardeners of his time.
To this end he says :

"in order to be as clear as possible, I have endeavored not to frighten
away every practical gardener and friend of gardening through useless
parade of science and erudition." (3b, p. 5.)

His point of view is well stated thus :

"However limited a flower garden, however small the corner of the
earth may be which a garden amateur can command, he is nevertheless
in a position to institute a number of useful investigations and note-
worthy experiments, to prepare for himself innumerable joyous de-
lights, when he succeeds, through artificial fertilization, in enriching
his little garden, his friends, his native region, with a new creation,
which owes its existence to his care and his intelligence. What pleasure
when he can extend these annuall}^ almost entirely at his will, with new
shades and colors never seen, obtain larger flowers, or bring about un-
limited doubling." {ib., p. 6.)

Lecoq enlarges upon the results that can thus be obtained in
fruit and vegetable gardening, and in agriculture :

"Although we possess already about five hundred sorts of grains, yet
we can still always obtain better ones, at least new modifications which
are better adapted to this or that soil or climate, or to all the conditions
of this or that agriculture." {ib., p. 7.)

The general method to be pursued is laid down simply as
follows : according to Lecoq's and the then prevailing point of
view, the first thing that one must strive after, in order to bring
plants to vary, is "the shattering of their stability, and the break-
ing up of their habit." For this purpose, it was considered desir-

PLANT HYBRIDIZATION BEFORE MENDEL 155

able to sow their seeds under different conditions of climate, tem-
perature, soil, moisture, etc. When, after several such sowings, a
case occurs where individual seedlings show more or less remark-
able changes, varying more or less, showing that stability or
habit has been unsettled, the seeds of the varying plants are to
be gathered, since from these, new varieties are to be expected.
The seeds of such new forms are sown over again and so on con-
tinually. Such changes Lecoq considers "purely morphological
phenomena, that is to say, changes of the natural form without
hybridization."

Once arrived at this point, hybridization of the thus newly-
obtained varieties was to continue, and still other new ones thereby
again obtained. Such was the simple formula of this genial friend
of plants and gardening, for the breeding and improvement of
plants. After a brief botanical discussion of natural fertilization,
Lecoq devotes the remainder of his book to a discussion of
artificial fertilization, first in its general aspects and applications,
and then in ^detail, as applicable to the various more important
families of the seed plants, of which he brings into discussion
seventy-five, including two hundred and ninety species.

Speaking of the hybrid offspring of the crossing of plants of
different genera or different species, Lecoq says :

"In general, the product of such a fertilization . shows at the same
time the characters and peculiarities of the father and of the mother;
but I have noticed that in a very great number of crosses achieved by
myself with all conceivable foresight, the hybrids or products have
almost always taken more from the mother plant than from the father."
(3b, p. 41.)

The reason for this might possibly be attributed to frequent
cases of accidental self-fertilization.
Again Lecoq says :

"The most difficult thing was and always is the shattering of the
stability of the first type, the breaking of its habit; just as soon as an
impulse thereto is present, then variation begins to know the limits of
which no human eye and no human understanding suffices. With the
mighty lever of hybridization in the hand, the power of the gardener is
an almost unlimited one." {ib., p. 45.)

Lecoq comes now to the discussion of special objects in the
breeding of plants. Speaking of breeding for double flowers, he
makes a remark that has genetic value.

156 PLANT HYBRIDIZATION BEFORE MENDEL

"One has almost the certair^ty of getting many double flowers, as soon
as one of the crossed species has become double, and in no wise was
the doubleness of both parents necessary, as many gardeners believe."
(ib., p. 45.) .

"Two plants with half-double flowers often furnish hybrids with very
double or completely double flowers ; but extremely seldom does the
case occur where two species with single flowers produce in the imme-
diately following progeny hybrids with double flowers." (ib., p. 46.)

With respect to color, Lecoq remarks :

"Most ordinarily, colors mingle, mix and fuse through hybridization
just as though one had put them together in a palette, and there arises
therefrom a middle or half tint ; but with many genera they do not fuse,
but remain separate, and appear as variegations on the corolla, as for
example in the morning-glory, tulip, etc. ; in stripes as in the aster ;
in flecks or clouds as in many varieties of Dahlia; in peripheral mark-
ings or borderings, as in some auriculas, primulas, etc." (ib., p. 47.)

Coming to matters of detail u^ith respect to the crossing of
plants in different families, there are a number of interesting re-
marks which deserve to be noted. In discussing the family of the
Cruciferae, Lecoq refers to the case of a cross by Sageret between
a cabbage and a black radish, the latter serving as the seed parent.
This hybrid is reported to have had two types of shoots, one super-
posed over the other, and both entirely distinguishable through
their form, one being like that of the cabbage, and the other re-
sembling the radish. This appears to be an interesting case of
factor-mutation in somatic cells. Lecoq mentions the further case
of a sectorial chimaera in Dianthus harhatus, which sometimes,
as he says, shows "variations" in which flowers of different color
occur not only on the same plant, but in the same inflorescence,
white and red flowers being immediately juxtaposed. His view
is as follows :

"plants which show these characters are hybrids, and confirm an ob-
servation made long since by Sageret, which my experience also verifies,
that one frequently gets hybrids which do not stand in the middle be-
tween father and mother, but appear to have taken on some organ or
other completely from the one and from the other, respectively, and
without any modification at all. I should at least scarcely know how to
explain the appearance of different colored flowers upon the same plant
in any other manner." (p. 117.)

In discussing the Leguminosae, Lecoq speaks of the crossing of
alfalfa, and alludes to the undoubted probability of successfully
crossing Medicago sativa, or ordinary alfalfa, with Medicago
lupulina or Yellow Trefoil, but remarks:

PLANT HYBRIDIZATION BEFORE MENDEL 157

"There appears to be no necessity for the creation of new plants, so
long as one has not already recognized, in those already present, essen-
tial defects or disadvantages, or on the other hand marked advantages."
(lb., p. 145.)

It is interesting here to remember that it is undoubtedly to a
natural cross of these two species that the Grimm variety of al-
falfa is due, which has enabled alfalfa growing to be carried into
the northern border states of the western United States, and the
western provinces of Canada.

Speaking of the crossing of agricultural plants in general,
Lecoq remarks :

"It certainly remains highly regrettable that thus far there has been
so little concern about hybridization of agricultural plants, and that it
has been simply left to chance to get varieties, while it would have been
so easy [referring here to beets] to institute with discretion crossing
experiments which certainly would be a new cause of agricultural
riches." (ib., p. 305.)

Lecoq lived before the days of the breeding of the cereals. Al-
luding to the breeding of wheat, he says :

"It remains one of the extraordinary human facts, that such a simple
operation, exacting neither time nor money, which can have such large
results, has thus far not been attempted on a plant upon which so many
families of all European lands are fed." (ib., p. 401-)

In conclusion it may be mentioned that Lecoq crossed a variety
of corn called Zea rostrata (corn with pointed or beaked kernels)
with ordinary yellow and red corn, and says :

"I completely destroyed the beak. Every single variety of this fine
plant brings out some kind of a change through hybridization, either
in the form of the cobs, or through the variegation of the kernels, or
through entire metamorphosis of the color." {ib., p. 398.)

BIBLIOGRAPHY

Duchartre^ P. E.

Rapport sur la question de I'hybridite dans les vegetaux,
mise au concours par I'Academie des Sciences. Annales des
Sciences Naturelles, Botanique, 4me Serie, 19:125-34. 1863.

Godro?i, D. A.

(a) De I'hybridite dans les vegetaux. Nancy, 1844.

158 PLANT HYBRIDIZATION BEFORE MENDEL

(b) Recherches experimentales sur I'hybridite dans le regne
vegetale. Memoires de I'Academie de Stanislas, 1862.
Nancy, 1863. pp. 287-98.

(c) Des hybrides vegetaux, consideres au point de vue de
leur fecondite, et de la perpetuite ou non-perpetuite de
leurs caracteres. Annales des Sciences Naturelles, 4me
Serie, Botanique, 19: 135-79. 1863.

3. Lecoq, Henri.

(a) Recherches sur la reproduction des vegetaux, 1827.

(b) De la fecondation naturelle et artificielle des vegetaux,
et de I'hybridation, consideree dans ses rapports avec
I'horticulture, I'agriculture et la sylviculture, ou etudes
sur les croisements des plantes des principaux genres
cultives dans les jardins d'ornementes, fruitiers, et
maraichers, sur les vegetaux economiques et de grande
culture, les arbres forestiers, etc., contenant les moyens
pratiques d'operer I'hybridation, et de creer facilement
des varietes nouvelles. 10th ed. Paris, 1845. German
trans, by Ferd. von Biedenfeld. Weimar, 1846.

(c) De la fecondation naturelle et artificielle des vegetaux,
et de I'hybridation, consideree dans ses rapports avec
I'horticulture et la sylviculture, contenant les moyens
pratiques d'operer I'hybridation ; et de creer facilement
des varietes nouvelles. 2nd ed. Paris, 1862.

4. Naudin, Charles.

(a) Reflexions sur I'hybridation dans les vegetaux. Revue
Horticole, 4me Serie, 4:3^-4. 1855.

(b) Sur les plantes hybrides. Revue Horticole, 4me Serie,
1861. pp. 396-9.

(c) Nouvelles recherches sur I'hybridite dans les vegetaux.
Annales des Sciences Naturelles, Botanique, 4me Serie,
19: 180-203, 1863.

(d) De I'hybridite consideree comme cause de variabilite
dans les vegetaux. Annales des Sciences Naturelles, Bo-
tanique, 5me Serie, 3: 153-63. 1865. Comptes Rendus de
I'Academie des Sciences, 59 ."837-45. November 21, 1864.

PLANT HYBRIDIZATION BEFORE MENDEL 159

5. Sageret, Augustin.

Considerations sur la production des hybrides, des variantes
et des varietes en general, et sur celles des Cucurbitacees en
particulier. Annales des Sciences Naturelles, Prem. Serie,
8:294-314. 1826.

6. Verlot, B.

Sur la production et la fixation des varietes dans les plantes
d'ornement. Paris, 1865.

7. Viimorin, Henry L. de.

(a) On the formation of races, varieties, and hybrids in
vegetables. Magazine of Horticulture, 19:314-16. 1863.
(Review of an article in the Revue Horticole.)

(b) Note sur une experience relative a I'etude de I'heredite
dans les vegetaux. Memoires Societe Nationale d'Agricul-
ture de France, 1879.

(c) Essais de croisement entre bles differents. Bulletin de la
Societe Botanique de France, 27:356-61 (December
1880). Also 30:58 (1883) ; 35:49 (1888).

(d) L'heredite chez les vegetaux. Conferences de I'exposition
universelle de 1889. Paris, 1890. Session of September
23, 1889.

Also, Heredity in Vegetables, Farmers' Magazine, Lon-
don, 1889.

(e) The selection of races of cultivated plants. Garden,
44 : 234-6. September 9, 1893.

(f) Pedigree or grade races in horticulture. In papers read
at the World's Horticultural Congress, pp. 10-19. 1894.

8. Vilmorin^ Louis Leveque de.

Notices sur I'amelioration des plantes par le semis, et con-
siderations sur l'heredite dans les vegetaux. Paris, 1859. New
ed., 1886.

9. Vilmorin^ Andre L. de.

Note sur I'amelioration de la carotte sauvage. Transactions
de la Societe Horticulturale de Londres, 1840. (Note reprinted
at the head of "Notices sur I'amelioration des plantes par le
semis," by Louis de Vilmorin, Paris, 1859.)

CHAPTER V 1

THE GERMAN HYBRIDIZERS

22. Wzegmatin's Experiments.

IN 1819, and for a second time in 1822, the Physical Section
of the Royal Prussian Academy of the Sciences, had, at Link's
proposal, offered a prize for an answer to the question: "Does
hybrid fertilization occur in the plant kingdom'?" (Gibt es eine
Bastarderzeugung im Pflanzenreiche'?) and this, despite the fact
that as early as 1761, Kolreuter had flattered himself with the
hope that now,

". . . even the most stubborn doubter of the truth of the sexuality of
plants would be completely convinced, if contrary to all conjecture," he
says, "there should be such an one, who, after a rigid examination, still
maintained the contrar>% it would astonish me as greatly as though I
heard someone on a clear mid-day maintain that it was night."

Fifty-six years after this utterance however, apparently un-
convinced, the Prussian Academy still sought light in the dark-
ness that Kolreuter had congratulated himself to have dispelled.

On the third of July, 1826, the Academy's prize was conferred
upon Dr. A. F. Wiegmann, physician, of Braunschweig. Since the
investigation did not, however, in the Academy's opinion, furnish
a complete solution to the question, only half, instead of the
whole of the prize was granted. The award was made in the
following language :

"The author has described the results of his investigations with appro-
priate brevity. These results are in part completely convincing, and in
part not;"

the reason being given, that certain of Wiegmann's hybrid speci-
mens submitted scarcely showed evidence of being of a hybrid
character. Since, on the other hand, Wiegmann's results com-
pletely confirmed and extended those of Kolreuter, and especially
by reason of his determination of the fact that self-fertilized
hybrids may bear fertile seeds, it was decided to grant the award.

PLANT HYBRIDIZATION BEFORE MENDEL 161

Wiegmann, through forty years of observation, including the
fact of having actually produced two geranium crosses as early
as his sixteenth year, was already predisposed toward the affirma-
tive of the question submitted. His investigations, begun in 1822,
were finally published in 1828 (7). In order to overcome all
possible criticisms from the opponents of the idea of sexuality in
plants, which he considered might be directed against what he
designates as "an unnatural handling of plants in pots," he con-
ducted his operations in the open ground, in connection with
which, he alludes to the several hindrances he was obliged to
undergo, "weak sight, a trembling hand, and painful bending and
kneeling." (7, p. 2.)

Wiegmann refers to the main failures encountered, including
the attempted repetition of a number of Kolreuter's experiments,
as being probably due in part to having attempted crosses be-
tween different genera.

"since many stigmas, according to my numerous experiments, take the
pollen of too distant genera either not at all, or with extreme difficulty."
(p. 2.)

"plants which together are to produce hybrids," he says, "must have
some relationship with one another, as Kolreuter has already remarked.
The nearer the parent plants are related to one another, the more easily
will hybrid fertilization succeed ; most easily in the case of different
sub-species or varieties ; then different species of the same genus ; less
easily in the case of plants of different genera." {ib., p. 26.)

Wiegmann, however, was entirely free from any rigid dog-
matic attitude on the species question. His views in this regard
are completely modern. Continuing the above, he says :

"Yet at the same time, one needs indeed pay less attention to differ-
ences based on artificial generic characters. Genera like Pisum and Vicia,
Ervum and Vicia, Lychnis and Cucubalus, are in their nature so related
that hybrids can arise from them, as Kolreuter and I have demonstrated."

"So much the more I dispute his opinion," he says of Kolreuter, "re-
specting the difference between true 'species' and 'variety' falsely de-
rived from the fertility or infertility of the hybrid plants." {ib., p. 25.)

Wiegmann, in fact, regards chance crossing in nature, between

species or sorts of plants, as having given rise to new agricultural

races.

"It appears from my experiments," he says (p. 26), "that many species,
or constant subspecies, e.g., Pisum arvense, Vicia leucosperma, Vicia faba
(red-seeded), as well as the most of the varieties of cabbage and the
cereals, whose origin is unknown, possibly are hybrid plants, which

i62 PLANT HYBRIDIZATION BEFORE MENDEL

have been produced upon our fields and in our gardens through the
proximity of a few related plants, and have remained constant." (p. 26.)

Wiegmann sums up the matter of the bearing of degrees of
relationship upon crossing as follows (p. 27) :

"Mainly it rests on the point that the different plants do not vary
from one another greatly in their natural constitution, and that their
secretions are not too heterogeneous, since otherwise the pollinating
substance would not be absorbed by the stigma.

"In general," he says, "foreign pollen takes hold of the stigma with
much greater difficulty than does its own, and in order to obtain com-
plete fertilization, one must often deposit it several times, even when
the foreign pollen is from a plant of the same species." (p. 3.)

Wiegmann's experiments covered a list of thirty-six crosses,
using the following species and cultivated varieties :

Avena, 3 species and varieties Ervum (lentil), 1 species

Allium (onion, etc.), 2 species Dianthus (pink), 3 species

Brassica (cabbage, etc.) 4 races Phaseolus (bean), 2 varieties

Nicotiana (tobacco, etc.), 2 species Verhascum, (mullein), 9 species

Pisum (pea), 1 species Vicia (vetch), 3 species

The general conclusions Wiegmann draws from his experi-
ments are most interesting. The most important are those which
relate to the possible vigor of new species.

"My experiments sufficiently prove," he says, "that the fertilization of
different subspecies, inter se, is a source of manifold degenerations of
species in the plant kingdom, and that insects, especially bees and bumble-
bees, as well as little beetles and flies, play a much more important role
in the fertilization of plants than one has lately been inclined to allow
them, but of which I have the indubitable proofs." (p. 3.)

"Even though the structure of the corolla in the case of leguminous
plants," he says again (p. 26), "scarcely appears to admit of the access
of insects and foreign pollen, yet the plants obtained from the seeds of
experimental plants show such a striking alteration in their specific
characters, especially in the form of the seed and its envelopes, that an
influence of foreign pollen on the ovules will scarcely be able to be
denied. I myself have numberless times convinced myself of the fact
that bumblebees, bees and small insects from the order of flies and
beetles, can fertilize the flowers of the Leguminosae in the manner stated
by Sprengel. It is therefore necessary in agriculture to give heed to this
matter, if one wishes to keep plants that are to be cultivated in their
quality and integrity."

With respect to observations of a more special nature, Wieg-
mann's memoir contains much interest. Regarding the breaking-up
of the progeny of hybrids, he says, speaking of K61 renter's obser-
vations :

"I have found his observations well founded, that the plants produced
from seed from one capsule of hybrid plants, often differ from one

PLANT HYBRIDIZATION BEFORE MENDEL 163

another in respect to fertility, and especially in the structure of certain
parts, now approximating more to the father, now to the mother." (p. 25.)

Wiegmann's independence of traditional authority is witnessed
in his contradiction of the view of "the great Linnaeus," that
hybrids resemble the mother in the fertilization apparatus, and
the father in foliage and habit. Instead, he says :

"The change through the foreign fertilizing pollen shows itself in very
different parts in different plants ; in the anther-filaments, in the in-
florescence, in the form, color, and odor of the corolla, in the height of
the stem and its divisions, in the form and outside covering of the leaf."
(p. 23.)

Referring to the then general assumption that hybrids (of the
Fi generation) occupy a mid-position with respect to their char-
acters between the two parents, he says :

"In many cases this does not occur, but either the color of the father
or that of the mother shows itself alone dominant (herrschend) in the
hybrid. The same also obtains among animal hybrids ; the two colors may,
through mingling, give an intermediate one, but in just as many cases
the one only prevails. Plant hybrids therefore unite in themselves in part
the peculiarities of the father, in part those of the mother, whereby they
approach now the maternal, now the paternal form." (p. 21.)

Regarding the matter of dominance, Wiegmann further inci-
dentally remarks upon the case of the crossing of two species of
Dianthus, where "the form of the father has almost entirely
suppressed that of the mother." (p. 22.)

For present-day genetics, one of the most interesting points in
Wiegmann's report is his discussion of the immediate effect of
the pollen in the case of leguminous plants. According to his
statement :

"Even immediately after fertilization, an alteration arising in the form
and color of the seed, and in the form and size of the pods, is especially
unmistakable in the case of the leguminous plants, although otherwise
all fruits and seeds of hybrid plants from other families have never
shown themselves to me to be different from those of the mother plants."
(P- 23.)

And again :

"The principle expressed by Gartner, that the influence of foreign pol-
len changes nothing in the form and external character of the fruits and
seeds of the mother plants, should, according to my investigations, un-
dergo a modification in the case of Diadelphia {Leguminosae) , since, in
the case of these, the foreign pollen exerts an immediate effect upon the
color and other characters of the fruits and seeds." (p. 29.)

In the case of Phaseolus, he says :

164 PLANT HYBRIDIZATION BEFORE MENDEL

"Previous experiments have taught me that Phaseoli of one species,
but of two different kinds of flowers and seeds, when placed together,
bear differently colored seeds, and, in the second generations, also differ-
ently colored flowers." (p. 23.)

Wiegmann carried on some field experiments with beans,
vetches, oats, and cabbage, in which adjoining rows of plants
were allowed to freely cross-pollinate through the agency of the
wind and insects, from which he concluded :

"It appears further, from the behavior of the Leguminosae and of
cabbage, that agronomists and gardeners cannot be careful enough in the
arrangement of their fields in order not to suffer from the great damage
through hybrid fertilization occurring even the first year." (p. 36.)

Speaking generally, he says further :

"It is not entirely improbable that that which exhibited itself to me
thus far, as being peculiar to the Leguminosae alone, may take place also
among other plant-families, and the clearing up of this matter remains
very desirable for botany, as well as for agriculture in particular."
(P- 30.)

Wiegmann's work, as a whole, impresses one as the work of a
man without scientific prepossessions, willing to investigate for
himself, and to dispute freely the authority of other investigators,
such as Linnaeus, Kolreuter, and Gartner, and, withal, a man
with a practical bias for and sympathy with agriculture.

23. The Work of Carl Friedrich von Gartner.

In the valley of the Nagold, in the Black Forest region of
Wiirtemberg, some forty miles southeast of Stuttgart, the capital,
lies the village of Calw.

Here Kolreuter, whose home was in Sulz, a little way to the
south, also in the Neckar valley, lived for a time, and did some
of his work in hybridization, in the garden of a local physician.
By a curious coincidence, in the same village of Calw in which
Kolreuter had previously worked, and but forty miles north of
Sulz, where the latter had formerly obtained the first hybrid plant
ever produced in a scientific experiment, lived and died Carl
Friedrich von Gartner, who for twenty-five years conducted ex-
tensive experimental work in hybridization. He was a physician,
and son of the distinguished botanist, Joseph Gartner, Professor
at Tubingen and St. Petersburg, and author of an authoritative
work on the seeds and fruits of plants, in which were figured
the morphology of more than a thousand species. The introduc-

,.*■'■

-V.V"

Plate XXXI. C. F. von Gartner, 1772-1850.

Plate XXXII. Village of Calw, in Wiirtemberg, home of C. F. von Gartner.

Plate XXXIII. Marketplace in Calw, Wiirtemberg.

PLANT HYBRIDIZATION BEFORE MENDEL

167

tion to the volume for 1778 contains, in the words of Sachs,
"valuable reflections on sexuality in plants."

In 1830, two years after the appearance of Wiegmann's mem-
oir, the Dutch Academy of Sciences at Haarlem, in turn, pro-
pounded anew the riddle of hybridization in the following words :

"what does experience teach regarding the production of new species
and varieties, through the artificial fertilization of flowers of the one

Plate XXIV. Present site in Calw of a portion of the former experimental garden of
C. F. von Gartner.

with the pollen of the other, and what economic and ornamental plants
can be produced and multiplied in this way?"

No reply was received (January 1, 1833), and the offer was
accordingly renewed for another three years until January 1,
1836.

In October, 1835, Gartner learned of the prize offer, and was
able to present a brief resume of his work up to that time, which,
indeed, prompted a further extension of time on the part of the
Academy. Gartner finally presented the Academy with a memoir
of two hundred pages, and with herbarium mounts of one hun-
dred and fifty different sorts of hybrid plants produced by hand

i68 PLANT HYBRIDIZATION BEFORE MENDEL

pollination. On May 20, 1837, this memoir received the prize,
and was later (April 20, 1839) published in revised and extended
form, together with an extensive list of the experimental material,
and with the obtained results arranged in tabulated form.

An idea of the amount of labor expended by Gartner during
the twenty-five years of his hybridization experiments may be
gathered by the statement that he carried out nearly ten thousand
separate experiments in crossing, among seven hundred species,
belonging to eighty different genera of plants, and obtained in
all some three hundred and hfty different hybrid plants, as the
total result.

Among the prominent genera worked with were Althaea, An-
tirrhinum., Aquilegia, Avena, Datura, Delphinium, Dianthus, Digi-
talis, Fuchsia, Gladiolus, Hypericum, Lobelia, Lychnis, Malva,
Matthiola, Nicotiana, Oenothera, Papaver, Primula, Ribes, Ver-
bascum, and Zea.

Number of
Number of attempted Number of

Genus

Spi

?cies u

sed

combina-

hybrid plants

in crosses

tions

obtained

Nicotiana (Tobacco, etc.)

432

Dianthus (Pink)

349

Lychnis (Campion)

137

Verbascunm (Mullein)

118

Lobelia

Digitalis (Foxglove)

Datura (jimson Weed, etc.)

Oenothera (Evening Primrose)

•9

Aquilegia (Columbine)

107 1332 366

Gartner undertook to classify hybrids for convenience into three
types: (1) intermediate, (2) commingled, and (3) definite. The
first included those in which "a complete balance occurred of both
fertilizing materials, in respect to either mass or activity." (2f,

P- 277-) ^

Commingled types are those in which

". . . now this, now that part of the hybrid approaches more to the
maternal or to the paternal form, whereby, however, the characters of
the parents, in their transference to the new organism, never go over
pure, but in which the parental characters always suffer a certain modi-
fication." {ib., p. 282.)

Under the third class of hybrids, Gartner places those

PLANT HYBRIDIZATION BEFORE MENDEL 169

". . . among which the resemblance of a hybrid to one of its parents,
either to the father or the mother, is so marked and preponderating that
the agreement with the one or with the other is unquestioned." (ib.,
p. 285.)

Gartner recognized, as did the other hybridists of his day, that

there was always a difference between the first and the succeeding

generations, the former being uniform, the later ones variously

splitting up. He made no distinction between the second and the

other following generations, but simply says that the fundamental

ground material of which the hybrid is made

". . . behaves differently in the second and in the further stages of
breeding, where, on account of the different nature of the two factors
of the hybrids in the succeeding fertilizations, an altered, shifting, vari-
able direction in type-formation enters into the arising varieties." (ib.,
p. 572.)

He further says, concerning variability in hybrids of the second

and succeeding generations :

"other hybrids, and in fact the most of them which are fertile, present
from the seeds of the second and further generations, different forms,
i.e., varieties varying from the normal types, which in part are unlike
the original hybrid mother, or deviate from the same, now more, now
less." (p. 422.)

His most definite statement, however, regarding what we call

"segregation" is as follows :

"Among many fertile hybrids, this change in the second and succeed-
ing generations affects not only the flowers but also the entire habit,
even to the exclusion of the flowers, whereby the majority of the in-
dividuals from a single cross ordinarily retain the form of the hybrid
mother, a few others have become more like the original mother parent,
and finally, here and there an individual more nearly reverted to the
original father." (ib., p. 422.)

Gartner did not fail to recognize the fact of unusual vigor in
hybrids, although he does not distinguish as to the generation.

"The marked increase in the size of the flowers is a phenomenon not
seldom occurring among hybrids [p. 295] and one of the most marked
and general characters of plant hybrids is the luxuriance of all their
parts, since, among very many of them,^ an exuberance of growth and
development of roots, branches, leaves and flowers manifests itself,
which is not encountered among the parents, even under careful cultiva-
tion." (ib., p. 526.)

Gartner recognized at once the possibilities for agriculture in

the fact of the increased vigor of hybrids, although, of course, he

did not realize the fact that this increased vigor belonged only to

a "hybrid" generation, as distinguished from Fo segregates.

lyo PLANT HYBRIDIZATION BEFORE MENDEL

"Among the characters of hybrids worthy of recommendation for agri-
culture, their tendency toward luxuriance in the stalks and leaves, and
their extraordinary capacity for tillering, is related above. With respect
to the raising of forage, agriculture could, without doubt, make great
use of this characteristic." (p. 634.)

Gartner derived, from his long experience, a certain, philosophy
concerning the nature of hybrids which is noteworthy. He recog-
nized an inequality in the influence of the relative "potency," as
he termed it, of one parent over another in a cross ; which potency
was maintained whichever way the cross was made. As now inter-
preted it probably means the relative dominance of one or more
factors of the respective parents. Gartner, not having the knowl-
edge which has come in consequence of Mendel's investigations,
sought a theoretical explanation for this phenomenon of domi-
nance and gave it the designation "sexual affinity" {W ahlverwand-
schaft) in the crossing of species, the magnitude of which he con-
sidered could be measured by the number of viable seeds produced
in the cross. He seems to confuse the matter by appearing to indi-
cate that there might possibly be a different number of seeds pro-
duced by the reciprocals of reciprocal crosses, thus presumably
indicating a possible "prepotency," so called, of one of the parents
in the cross. In other cases he seems to mean simply the relative
influence, so to speak, of such and such species when crossed with
others. This appears to be the meaning in the following :

"This manifestation of generic types, according to which one species
operates in a predominant manner over several other species in hybrid
breeding, is a further incontrovertible proof that the relationship of the
forces, through which the union of two pure species takes place, must
be unlike, and that thereby there can be no question of any balance of
factors." (2f, p. 290.)

It will be seen that Gartner's view of hybridization was that
"species" was crossed with "species" as such, each species as a
whole exerting its own relative power or "potency" in the cross —
the hybrid being regarded as the resultant, so to speak, of the
contest for supremacy of the two competing natures in the com-
pound. This view is well enough expressed in the following pas-
sages :

"Thus, just as there are species in a natural genus, which possess a
prepotent fertilizing power upon several other species of their genus, so
there are also species which exert upon several others such a typical pre-
dominating effect, not to an equal extent to be sure, but still of such a

PLANT HYBRIDIZATION BEFORE MENDEL 171

nature that their operation, in all combinations is to be recognized by a
character in common.

"Both of these forces, are, however, of different kinds, and follow
different laws." (p. 289.)

Gartner did not realize, in spite of Sageret's experiments, that
some individual characters of a parent might be found to domi-
nate in a cross and others not.

"The laws of hybrid types orient themselves," he says, "not toward
the individual organs of plants — do not apply to a single part, e.g.,
stems, leaves, etc. — but are applicable rather to the inner natures of
species. The organs which determine the types of hybrids must therefore
be investigated and compared in their totality and in their natural
interrelationship. For the most part, the peculiarity of a hybrid expresses
itself in its entire aspect; only in this respect the flower is most fre-
quently and plainly distinguished above other parts of the plant."
(p. 251.)

We do come, however, upon a form of utterance that is some-
what singularly Mendelian in character:

"in the formation of simple hybrids, as in sexual reproduction in gen-
eral, two factors are active. This unlikeness of activity, flowing from
the specific difference of species, expresses itself through the more pro-
nounced or the weaker manifestation of the individual paternal characters
in the different parts of the hybrid. Whether the total nature of the
species and its formative impulse determines the direction and form
of the type, or whether the individual parts of plants have a special
influence upon the modifications, may not be determined without further
investigation." (p. 257.)

Gartner made some crosses with corn and with peas, to deter-
mine the question of the immediate influence of the pollen upon
the character of the seed. In corn he got no results, because of
crossing white corn with red, in the case of which latter, the color,
being due to the skin or pericarp, does not show itself until the
following season. Because of the importance of the later genetic
results with Pisum and Zea mays, it will be of interest to follow
in some detail Gartner's work in the crossing of plants of these
two species.

The following comment is made upon Knight's experiment with
peas :

"Th. Andr. Knight, in the year 1787, instituted experiments with Pisum
sativum fructo-albo (Common White Pea) and P. sativum fructo-cinereo
(Grey Pea), which were first made public in the year 1799, concerning
which he noted that the pods obtained from these artificial fertilizations
were not markedly different from those of the ordinary seed capsules
of this variety {Pisum album) ; from which he derived the conclusion
that it was probably true, that the outer hull of the seed of Pisum, as

172 PLANT HYBRIDIZATION BEFORE MENDEL

he had also found with the other plants, was entirely formed by the
female orgaiis. Of the change in the color of the seeds no mention
occurs here ; yet it is to be expected of Knight that this should not have
escaped him, if it had actually taken place in the case of his seeds. In
a later appearing report of this celebrated agricultural writer, the altera-
tion in the color of the seeds of peas through artificial pollination is
conceived, but in the second generation, however." (p. 80.)

In view of a number of previousl}^ reported results with respect
to the immediate influence of foreign pollen upon the seed and
the fruit, Gartner undertook, in 1829, a series of experiments of
his own to this end. For this investigation he chose the following-
named varieties of garden peas :

1. Parisian Wax Pea, tall, with white flowers, designated as
Pisum sativum luteum

2. Red-flowered Sugar Pea {Pisum sativum macros per mu7n)

3. White-flowered Creeping Pea with yellow seeds {Pisum sa-
tivum nanum repens)

4. Early Green Brockel Pea {Pisum sativum viride).

All of them, as he states, were constant and well-marked vari-
eties. The results may be summarized as follows (3f, pp. 80-6) :

I. P. sativum luteum X P- macro spermum.

The seeds from the four flowers pollinated gave 16 round
yellow seeds of the same size and form as the self-fertilized
flowers.

II. P. sativum luteum X ^- sativum viride.

From the five flowers pollinated the pods contained as fol-
lows;

1. 4 round-oval seeds of the same size as the self-fertilized,
of greenish-yellow color

2. 6 round seeds of dirty-yellow color

3. 1 seed, greenish-yellow

4. remaining unfertilized

5. 1 round seed, greenish-yellow.

Gartner says (p. 82) :

"All these seeds in the following year (1830) germinated well, and
furnished five sound plants."

Of the color and form of the seeds of these plants, however, he
makes no report.

PLANT HYBRIDIZATION BEFORE MENDEL 173

III. P. sativum macrospermum (very tall, with purple flowers
and greenish-yellow seeds) X P- sativum nanum repens
(with white flowers and yellow seeds).

From four flowers pollinated fruits were obtained, containing
as follows :

1. 4 "somewhat more dirty-yellow seeds than those of the
maternal parent, which are more greenish," an evident
observation of dominance

2. 4 seeds similar to the above

3. 4 seeds which did not mature

4. 4 seeds similar to (1).

IV. Pisum sativum nanum repens X Pisum sativum viride
(with white flowers and green seeds).

Four pods were produced. The result as to the seeds is reported

as follows :

"On complete ripening and desiccation of the pods and of the seeds,
there was, however, no essential difference to be described between those
arisen from natural (maternal) fertilization, and those arisen from
hybridization ; only that the hybrid peas appeared to be somewhat more
round and less uneven. The color was not different." (p. 83.)

V. Pisum sativum 7ianum repens (with white flowers and yel-
low seeds) X ■^- sativum viride. Six flowers were pollinated,
producing altogether 22 seeds, which all appear to have
been round with greenish-yellow color.

VI. Pisum sativum viride (with blue or green seeds) X •^•

sativum luteum.
But one flow^er was pollinated, producing a single seed

". . . which was not decidedly yellow, still less blue or green, but dirty
yellow, thus incontrovertibly changed in color, since the flowers left to
self-fertilization furnished simply green or blue seeds." (p. 84.)

VII. Pisum sativum viride X P- sativum macrospermum.

Five flowers pollinated, from which-- four pods were obtained,
containing in all 12 seeds, all round and yellow, with the excep-
tion of one that did not come to maturity.

VIII. Pisum sativum viride X P- sativum nanum repens.

One flower pollinated; five seeds produced, all pale yellow.

Gartner did not follow out the distribution of form and color
in the seeds to the second generation. The statement which most

174 PLANT HYBRIDIZATION BEFORE MENDEL

nearly approaches to a conclusion in this regard, is found on
p. 326, as follows :

"The above-mentioned change in color of the seeds of Pisum sativum
through hybrid fertilization comes out in the second generation more
definitely and more decidedly than in the first immediate hybrid product
through the immediate influence of the foreign pollen, whereby a quite
similar relation as in Mays and other seeds is produced." (p. 326.)

Again (3f, p. 496), speaking of the "running out" of certain

Leguminosae^ he says :

"Already above [p. 82], several varieties of Pisum have been under
discussion and exact experiments have been reported, whereby it has
been demonstrated that, through fertilization, such an alteration in the
seeds is effected, that in the plants deviations from the previous condi-
tion come to light."

Gartner's most general statement, however, regarding the sec-
ond hybrid generation appears to be as follows (z^., p. 422) :

"In many fertile hybrids, this alteration in the second and further
generations affects not only the flowers, but also the entire habit, even
to the exclusion of the flowers, whereby the majority of the individuals
of a single breeding ordinarily retain the form of the hybrid mother, a
few others here become more like the stem-father."

Concerning the influence of foreign pollen upon the immediate
form and color of the hybrid seed, Gartner reports further upon
his experiments with Zea mays. Having maintained constant a
Zea mays nana strain with yellow seeds and a Zea mays major
strain with red-striped seeds, in cultivation in his garden for sev-
eral years, in 1825, he crossed thirteen ears of the yellow with
pollen of the red-striped strain, from which but a single ear with
five seeds developed.

"The five perfect seeds were neither in size or color in the least dif-
ferent from those of the mother, so that immediately after the com-
pleted ripening of the seeds, it appeared doubtful whether really a
hybrid fertilization had taken place with them ; the germination in the
following year, however, . . . placed the hybrid fertilization of the
plants obtained in a clear light ; so that it proceeds uncontradictably
therefrom, that with Zea mays the pollen of an otherwise colored species
or variety only changes the nature of the embryo, not, however, the
external quality and color of the seeds." {ib., p. 88.)

Gartner, of course, was unable to distinguish between the be-
havior of endosperm and pericarp color in maize crosses.

His investigations on color-inheritance in the seeds of Indian
corn, were induced by the facts of color-inheritance in the seeds
of peas. He states :

PLANT HYBRIDIZATION BEFORE MENDEL 175

"There was under discussion [p. 80] the matter of the immediate work-
ing of the foreign pollen upon the quality and color of the seeds, and
the fact was cited that the genus Pisum shows the peculiarity, that the
seeds of the different varieties of Pisum sativum assume immediately an-
other color through the foreign pollen : therefore arose in our case the
presumption, that this would likewise also obtain with the different
varieties of Zea mays. Earlier experiments with Zea mays, by R. J.
Camerarius, Logan, Pontedera, and Henschel, which Schelver has assem-
bled, give no information on this point." {ib., p. 322.)

In 1824, as stated above, Gartner pollinated Zea mays nana
with small yellow seeds, with pollen of Zea mays major^ with
grey, red, and striped seeds. Of the various pollinations (on thir-
teen plants), only one of the crossed ears grew; viz., the one pol-
linated from a plant of the red-striped variety, which produced
five seeds.

In 1825, these five seeds were grown, and produced four ears.
Two of these had only yellow seeds, somewhat larger than those
of the female plant. Of the two others, however, one ear had 64,
out of 288 seeds, "more or less reddish and gray" ; the other, out
of 143 seeds, had 39 which, like the preceding, were more or less
colored.

"it is, however, to be remarked that the yellow color of these inter-
mingled yellow seeds was not pure yellow like that of the maternal
parent, but dirty yellow; thus, therefore, as well in size as in color
somewhat altered," {ib., p. 323.)

The experiment was carried over to the second generation.

For further determination as to the alteration of the colors of
the seeds obtained in the preceding experiment, the seeds from
each ear were separated, especially according to the colors, into
four parts, and sowed apart, in order to obtain the result, in
the second generation, of each color separately. The seeds were
divided into :

(a) pure yellow (c) clear grey

(b) dirty yellow (d) dark reddish-grey. (p. 323.)

The pure yellow seeds, (a) above, produced 5'9 ears, 32 of
which bore yellow seeds ; several others are reported to have had
only a few colored seeds ; in the case of several, there were "a
number of seeds dissimilarly colored, distributed at random, but
by far the greater part of the seeds were yellow."

The dirty yellow seeds, (b), gave 5 ears, on which markedly
more colored seeds were found than on the ears from (a), the

176 PLANT HYBRIDIZATION BEFORE MENDEL

great majority being yellow. There was no ear with yellow seeds
exclusively.

The clear grey seeds, (c), produced two ears, on which the pro-
portions of seeds were reported as follows : pure yellow, ^4 ; yel-
low and speckled grey, about ^g ; reddish-grey, 1/12 ; and dark
reddish-grey and brownish-red, ^.

This is the only instance in Gartner's maize experiments in
which the numbers in the second generation are reported.

The seeds of (d) did not germinate.

While the experiment has not particular genetic value, inasmuch
as the parents were not selfed lines, and close-pollination is not
reported as having been effected in the case of the F^, the work is
interesting historically.

Gartner considered the fact noteworthy, as he states (p. 325)
that red-and-yellow striped seeds were derived from the grey
seeds, and notes that the stripes concentrated about the point of
insertion of the style, his actual object of investigation being to
determine whether, in the case of Zea mays^ as in Pisum^ an im-
mediate effect was produced by foreign pollen. He considered the
fact to have been demonstrated in the negative by his experiment.

"since it is, however, determined, that the color of the seeds of Zea
mays do not immediately undergo an alteration through foreign polli-
nation, but that the capacity for the color change indicated is first pro-
duced in the germ through hybrid fertilization, and the different colors
of the seeds appear for the most part separate and without order on the
ears of the second generation ; it is therefore to be doubted that the
previously mentioned stripes produced in the second generation through
the fertilization process with their own pollen proceed from the point
of insertion of the pistil (stigma), but that they proceed rather from
the base of the seed, run through the outer layer of the testa, and unite
at the apex of the seed at the base of the pistil ; so that the reason there-
for is to be sought, not in the fertilization material, but in the rudiment
of the unfertilized egg." {ib., p. 326.)

The remark is of interest as a sort of genetic conclusion, in
which morphological reasoning was involved, the fact of the con-
veyance of the stripes in the seed toward the base of the stigma
being assumed by Gartner to be prima facie evidence of the fact
that the "influence" of the pollen ("Befruchtungssubstanz") af-
fected the morphology of the seed from the point of entrance of
the pollen into the ovary at the base of the stigma. Since this rea-
soning antedated any knowledge of the manner in which fertiliza-
tion actually took place. It is not particularly surprising. It is.

PLANT HYBRIDIZATION BEFORE MENDEL 177

however, unfortunate in Gartner's case that he was unable to
differentiate between endosperm color and pericarp color, which
latter he was actually dealing with. Consequently, his experiments,
while proving to his mind the fact that the immediate effect of
cross-fertilization did not appear in the case of the seeds of maize,
is, of course, wide of the mark, since the appearance of stripes
in the presumed "second" generation was the normal F^ appear-
ance of pericarp color.

Gartner's work is noteworthy, not only for the remarkable
number of species with which he experimented, but for the scru-
pulous care which he exercised in his operations, if we may judge
from his own statements, as for example, the following :

"For complete assurance of the purity and reliability of the products
of hybrid breeding, and for testing the conclusions derived therefrom,
we have repeated most of the experiments, especially the doubtful cases,
not only once, but several times, and put them to the test through cross-
ing of the same species; for, even with the most scrupulous foresight
and precision, individual and rare instances have still occurred in these
tedious and wearisome investigations, where the suspicion had made
itself felt of a mistake or error having crept in, either in pollination or
emasculation, since such results stood in direct contradiction to the usual
experiences and, on a repetition of the experiment, made themselves in-
controvertibly evident as an error. We believe it possible to attain no
higher degree of certainty in this branch of natural science, and to be
able to bring the conclusions derived therefrom to no higher proofs,
than through the precise coincidence of the forms of the products, by
repetition, under the same conditions with the same species, but with
different individuals and at different times." {ib., p. 675.)

In closing this account of Gartner's work, it will be of interest
to note Focke's comment in his "Pflanzenmischlinge."

"Gartner's 'Versuche und Beobachtungen' contains the essential con-
tents of the prize essay for which an award was offered by the Royal
Netherlands Academy of Sciences in 1830, and the contributions con-
tained in his scattered papers." (1, p. 438.)

As Focke says :

"The work, although rich in contents, is unfortunately of an extraor-
dinary clumsiness, and is therefore, on the one hand, insufficiently
known and, on the other hand, frequently overrated." {ib., p. 438.)

"Concerning the reliability of the assertions, one can only with dif-
ficulty form a definite judgment, since the book swarms with numberless
inaccuracies and contradictions : A careful special study has forced upon
me the conviction that the errors in Gartner's work have proceeded from
an extraordinary lack of authorship, and the inability lucidly to arrange
the observations and facts." {ib., p. 438.)

"So far as concerns the material which Gartner worked upon, his in-

Qi^^iQAc

178 PLANT HYBRIDIZATION BEFORE MENDEL

vestigations on hybridization move almost exclusively within the pre-
viously indicated lines of Kdlreuter. He has especially experimented with
the same plant genera in which Kolreuter attained success ; he has in-
contestably demonstrated great persistence and restless industry in his
numerous experiments, but has scarcely done anything else than to con-
firm or carry further the Kolreuter investigations. As rich a source of
the knowledge of hybrids as the Gartner work indeed is, one must yet
never forget that it must only be used with great caution and critical
circumspection." {ib., p. 438.)

Focke's accurate summary is sufficient as a description of the
Gartner memoir. The endeavor has been to present herein the
essential facts and observations, as well as the more important
conclusions which it contains. In conclusion, however, with due
deference to Focke's criticisms, it may be said, attention should be
called to what may be considered one of the most fundamental
types of expression upon the subject treated.

The physiological nature of a "species" is stated in the follow-
ing sentence :

"The essentiality of the species, therefore, consists in the definite re-
lationship of its sexual powers to other species, which relationship, to-
gether with specific form in each species, is a peculiar, special and con-
stant one. Form and essence are in this connection one." (2f, p. 163.)

And again :

"Not the external similarity in the form and habit of species, but the
harmony of the inner nature, gives the capacity for hybrid fertilization :
both are likewise not always harmoniously bound together." {ib., p. 186.)

In this statement is revealed a real comprehension of the phy-
siological nature of species ; which comprises something else than
the elementary conception of trying-out the crossing of supposed
species for the purpose of determining whether their offspring are
or are not sterile ; the former case proving the parentage in ques-
tion as belonging to different ''species,'' the latter, as being merely
"varieties'' of the same species. xAlthough the process may be the
same in both cases, the method of presentation above shows a
deeper conception of the process involved.

24. Wichura and the Hybridization of Willows.

In 1865 appeared Wichura's memoir on the hybridization of
plants (5), based upon experiments in the crossing of willows
which had occupied him from 1852 to 1858, inclusive. A brief
preliminary report had appeared in "Flora" in 1854, and also
within the same year in the report of the Schlesische Gesellschaft.

PLANT HYBRIDIZATION BEFORE MENDEL

179

Taken as a whole, Wichura's work dealt, not with the investi-
gations of individual specific characters, but with species taken
entire and treated as such. As was the general custom, he regarded
a "species" as an integral w^hole, that could be crossed in its en-
tirety. With this conception he made what he called "binary,"

Plate XXXV. Max Ernest Wichura, 1817-1866, Jurist, Botanist, Regierungsrat at Breslau
(1859-1866).

i8o PLANT HYBRIDIZATION BEFORE MENDEL

"ternary," and "quaternary" crosses, i.e., crosses (l) between two
species; (2) between a species and a hybrid; and (3) crosses be-
tween two hybrids. Besides the smaller list of Wichura's successful
crosses, he published a much longer one of his failures, which
stands as evidence both of the considerable amount of crossing-
work that was done, and of the scientific integrity of the experi-
mentor.

Of the ordinary, or, as he calls them, "binary" crosses Wichura
made in all thirty-five successful crosses and combinations of
such (of which ten were strictly "binary," i.e., simply crosses in
the ordinary sense), between twenty-one different species of wil-
lows.

Although, as has been stated, Wichura, similarly to most of the
other hybridists of his day, paid no attention to the crossing of
characters taken as units, he remarks upon the evidence of indi-
vidual characters being inherited as such :

"It was of interest," he says (6, p. 27), "to observe how the unusual
narrowness of the leaves in the experiment, utilizing Salix purpurea X
viminalis, remained still recognizable in the following generation ; a
proof that even in hybrid fertilization individual characteristics of the
parent plants can be inherited."

Wichura noted in willows, as others had done in other plants,

the fact of a higher degree of sterility on the part of hybrids

obtained between species of more distant specific relationship. The

greater amount of vegetative vigor of hybrids was remarked upon

by Wichura in the following words (6, p. 40) :

"Not only in the reproductive organs, but also in their vegetative be-
havior, hybrids show many phenomena whereby they are more or less
strikingly distinguished from true species. According to the corroborating
observations of Kolreuter and Gartner, a larger part of the hybrids ob-
tained by them through hand crossing were distinguished by luxuriance
of growth. The plants grew to a greater height than the parents, spread
out farther laterally by virtue of an increased capacity for sprouting,
had a longer life-period, were able to withstand cold longer, and had
more abundant, larger, and earlier flowers than the parents. . . . Among
the willow hybrids, similar phenomena occur, but the example of luxu-
riant growth by no means constitutes the rule."

Wichura further observed that :

"Even the most fertile hybrids fall behind the parents in their produc-
tiveness. A certain deficiency in the parts set aside for reproduction must
therefore also occur with them, if we associate this in reverse relation
with the excess of their vegetative development, it stands in complete
harmony with the facts otherwise demonstrated. We shall therefore have

PLANT HYBRIDIZATION BEFORE MENDEL 181

to say, in order to express the relationship correctly, that in the case of
very vigorous hybrids the weakness of the sexual parts brings out an
increased development of the vegetative growth, whereas it is not the
case with others which are too weak for such reaction [meaning crosses
between two distant species]." (6, p. 43.)

Wichura concluded from his observations that hybrids were
intermediate in respect to the differing parental characters. Cases
of dominance do not seem to have come under his hand.

"Among the numerous artificial and natural willow hybrids observed
by me," he says, "I have throughout verified but one apparent exception
to the principle of intermediateness.

". . . Even the time of flowering of hybrids holds the mean between
the times of flowering of the two parents." {ib., p. 47.)

"As rich in species as the genus of the willows is, and as numerous
combinations of hybrid fertilizations as it has to show, nevertheless I
have never yet verified anything of a preponderant influence in any one
of its species, but rather always found that their hybrids hold the mean
between the constant characters of the parents." {ib., p. 50.)

"In hybrid fertilization, if unlike factors [Factoren] unite, there arises
an intermediate formation, etc." {ib., p. 86.)

The latter passage appears to be the first occasion where the
term "factor" has been used in the literature of plant breeding,
although here the "factors" referred to are perhaps the parents
as a whole which participate in the cross, rather than the charac-
ter-forming units from those parents.

His general conclusion is (ib., p. 46.) :

"Constant characters, through which the parent, species are distin-
guished from one another ... go half over to the hybrid, so that it
holds the middle position between them."

Two observations of Gartner's were verified by Wichura — the
identity of reciprocal crosses (pp. 51 and 186), and the fact of
"variation" in hybrid progeny.

As to the question of the relative importance of the egg or the
pollen in the result of fertilization, Wichura says (p. 57) :

"One sees the question is still far removed from having been brought
to light, but from Gartner's and my own observations it appears at
least determined, that the products of hybrid pollen in breeding are
more various than those of the pollen of true species."

Regarding the generally observed identity of reciprocal crosses,
Wichura draws the following conclusion (p. 86) :

"We have found that the products which come from reciprocal cross-
ing, unlike the well-known experiments made in the animal kingdom,
completely coincide with each other.

"From this it must follow, however, with mathematical necessity, that

i82 PLANT HYBRIDIZATION BEFORE MENDEL

the pollen cell must have exactly the same share in the conformation of
the fertilization product as the egg"

So far as the writer knows, this is the first complete categorical
statement in the literature of plant breeding of such a conclusion
as to the behavior of the sex cells in amphimixis.

One is completely impressed, in reading Wichura's work, with
the scrupulous care, accuracy and precision with which his hybrid-
ization experiments were carried out. One or two passages in
point are interesting. Referring to a case of Gartner's, where ex-
ceptional types appeared in the midst of "a greater number of
hybrid plants of completely similar types," he says (p. 53) :

"To judge concerning the here-mentioned exceptional types, without
myself having seen them, is scarcely possible. From the relatively lim-
ited number of my experiments, which have not yielded the like, I
cannot, to be sure, deny its possibility; but here likewise, as above in the
case of reversions, there is the suspicion of the existence of a complete
disturbance of the experiment, whether that the protection had not been
complete, or the pollen utilized for fertilization not pure, or the seeds
sown not free from foreign admixture. Whoever knows from his own
experience how much care must be observed in order to keep an experi-
ment clean, becomes skeptical respecting all results of an experiment
which vary from the usual rule, of the correctness of which one has not
achieved conviction through his own observations,"

Regarding these and other so-called anomalies as the result of

crossing, he again says (p. 89) :

"That concerning all these points and many other disputable questions
, , , we know so little has indeed its basis in part in the method hitherto
of artificial cross-fertilization, which suffers from the double deficiency,
that the care requisite to the correctness of the experiment, through the
exclusion of foreign pollen, had not been taken in the first place, and
secondly that, although many experiments have been instituted in very
different families, nevertheless the individual hybrids have not been
bred and observed in sufficient numbers. However, this is imperative
throughout for attainment of general results. Only when one has at
hand the same hybrids in hundreds of cases, partly from the same, partly
from different parents, repeated through different years, only then will
one be in a position to separate the essential phenomena of hybridization
from the more accidental ones,"

Finally (p. 92), Wichura remarks, expressing the hope that a
learned society or an individual with means might repeat his own
experiments on a larger scale :

"The most scrupulous exactness in such case would be indispensable.
Failing this, and especially if the possibility of the access of foreign
pollen is not completely excluded, then all experiments, the more ex-
tensively they are undertaken, only contribute the more to the confusion
of the matter. This must be taken to heart,"

PLANT HYBRIDIZATION BEFORE MENDEL 183

Regarding the possibility of securing a cross in any given

case, Wichura remarks (p. 84) :

". . . Only such species can be united in a' hybrid, which agree in rela-
tively many characters, and correspondingly in many life conditions.
Experience teaches the same thing in the familiar rule, that hybrid
combinations only occur between species of the same genus, or different,
yet nearly related, genera."

He comes to a generalization of genetic value in the following

statement (p. 85) :

"It is known that families die out after a few generations whose mem-
bers carry in themselves the germ of a disease, and who mate only among
themselves; and variety breeders know very well that all diverging char-
acters of animal and plant species may be intensified when, in successive
fertilization, the precaution is taken that only similarly divergent in-
dividuals mate with one another."

25. Kegel on Hybridization.

The views of Regel (5) on hybridization, also illustrate in an
interesting manner the general attitude of the hybridists of the
time on the subject of the products of crossing:

"The hybrid plant always originates through sexual intermingling of
two parent species, actually different from each other. Plant forms which
have originated through mutual fertilization of different varieties of
one and the same species are not real hybrids, but are frequently falsely
regarded as such." (5, p. 59.)

Regel designates the former as "true," and the latter as "false"
hybrids.

This point of view has, of course, long since been completely
superseded by the point of view expressed by the term "the hybrid
condition," with respect to such and such characters possessed by
the plant. Regel carried on experiments in 1846, in the crossing
of Calceolarias, in which he found that, in respect of the essential
characters, the hybrids occupied an intermediate position between
the two parents.

26. Carl Wilhelm von Ndgeli and the Hybrid Question.

In 1865 Carl von Nageli (4c) presented a survey of the work
of the earlier hybridizers. The occasion for the discussion, he says,

". . . presented itself to me from an investigation of the signification
of the intermediate forms occurring in nature between many species."
(4c, p. 187.)

The theme of hybridization, he says, is of importance because
". . . it sheds light upon reproduction, in so far as it is the question

Plate XXXVI. Carl von Nageli.
( !ri1 - iS'^l

PLANT HYBRIDIZATION BEFORE MENDEL 185

concerning the manner in which the characters of the parents are carried
over to the offspring." {ib.)

Concerning the question whether hybridization could be used

to reveal the then much-disputed difference between "species" and

"variety," Nageli concludes that between species and varieties

there exists no essential difference, in characters which either the

external form, the internal structure, or the chemical composition

exhibits, but that there is simply a gradual intergradation between

the two.

"If we compare species and varieties with regard to sexual affinity, we
find no boundary which divides them. In general, the relationship is, of
course, greater between varieties and lesser between species." (4c, p. 200.)

This being the case, there can be no point in making the be-
havior of hybrids determine whether the parents of the cross
were "species," or "varieties," and yet, as Nageli remarks:

"By far the most numerous and the most important investigations on
hybridization have been carried on by decided adherents to specific
fixity."

Elsewhere Nageli refers to the origin of species and varieties

in the following words :

"For, when it becomes apparent that varieties are not the consequence
of external influences, but are brought a^bout through inner causes, then
the difference in principle between specific and varietal, constant and
variable characters, is removed. One must then assume, from the tendency
to vary in the plant independently from without, that it is the specific
nature itself which determines variety formation. Between species and
variety there exists then a causal relation, and the relation finds its
logical expression in the principle that the species is nothing but a fur-
ther developed variety." (4a, p. 104.)

"The formation of more or less constant varieties or races is not the
consequence and the expression of outer agencies, but is brought about
through inner causes." {ib., p. 105.)

After enumerating the list of experimenters and investigators

in the field of hybridization, he says :

"if, in spite of these numerous experiments, no greater agreement
with respect to hybrid-formation in the plant kingdom prevails, the
reason may reside in various circumstances . . . Proceeding from the un-
alterableness of ^pecies, the endeavor is above all to determine the
difference between species-hybrid and variety-hybrid — a difference which
in reality does not exist." (4c, p. 89.)

In this paragraph, Nageli briefly states the unfortunate situa-
tion into which the study of hybrids had fallen. In a word, the
whole matter of the study of hybridization was largely used as a
means for determining degrees of distinction between species.

i86 PLANT HYBRIDIZATION BEFORE MENDEL

Nageli comments truly on the meagre range of information
which many investigators possessed, proceeding either from obser-
vations of supposed hybrids in nature, or from conclusions derived
from their own scanty experiments, which :

". . . on account of their incompleteness, and frequently on account of
their inexactness, were unavailable for new theory." (4c, p. 190.)

He then pertinently remarks :

"The knowledge of hybridization would in recent times have made
more progress, if many observers, instead of beginning anew, had made
use of the results of the first-two-named German investigators fKolreuter
and Gartner], who applied the labor of their lives to the solution of this
problem." (4c, p. 190.)

Here Nageli strikes at a weak point not only in the science of
his own day, but of a later time. Resting upon the experiments
of Mendel, investigators have too frequently overlooked the sug-
gestions to be found in the work of the pre-Mendelian students of
hybridization. Concerning the then existing state of the knowledge
of crossing, he says :

"No field of knowledge is less complete ; and continued, critically con-
ducted experiments are in the highest degree desirable, but they can
have scientific value only when they rest upon the knowledge ot what
has already occurred ; when they either verify the already determined
laws through new facts, or modify, extend or limit them ; in the latter
case, however, showing the conditions under which these modifications
appear." (4c, p. 190.)

Nageli indulges in a gleam of wit at the expense of those who
felt no quarrel over the species question so far as hybridization
was concerned, but who relied upon the rule, that at least only
species of the same "genus" could hybridize, and that therefore
those species which possessed the capacity to cross must be united
in the same "genus." He remarks :

"if I say that all wines belong to the genus 'liquid' it does not follow
therefrom that every liquid has to be a kind of wine, and that everything
that is not a wine must on this account also be no liquid." (4c, p. 192.)

In order to assist in obtaining a picture of the status of hybrid
theory at the time of the publication of Mendel's paper, it will
not be without interest to note the substance of the series of nine
conclusions given by Nageli in his paper "Die Bastardbildung
im Pflanzenreiche" (4c), presented before the Akademie der Wis-
senschaften at Munich, December 15, 1865. It will be noted that
most of these so-called "rules" bear generally upon what plants

PLANT HYBRIDIZATION BEFORE MENDEL 187

will cross, whether the progeny are likely to be fertile or not, and
the general appearance of the hybrid with respect to the parents.
Briefly summarized, these are as follows :

1. "That plant-forms, which stand systematically near together, can
form crosses with one another." (4c, p. 191.)

from which it follows conversely that systematically nearly
related plant forms may cross, the limit for crossing in general
not exceeding the genus, and very often not going beyond the
same section of the genus, and sometimes remaining within the
species, different natural orders and genera differing in this re-
gard.

2. "plant-forms cross with much more difficulty and, on reciprocal
fertilization, give a much scantier number of fertile seeds, the less they
are sexually interrelated. This sexual affinity is not the same in signifi-
cance as systematic affinity, which makes itself evident through external
differences in form, color and habit, nor as that of the inner relationship,
which is based upon the chemical and physical constitution." {ib., p. 193-)

Varieties and species cross with the greater difficulty, and in
reciprocal crosses produce the smaller number of fertile seeds, the
less closely related they are sexually. This "sexual affinity" is
taken by Nageli not to be identical with systematic relationship
as determined by morphological characters, color or habit, nor
with the inner chemical or physical constitution. Just what "sexual
affinity" thus implies is not entirely evident. Nageli illustrates
the fact by the case of two plants, A and B, in which A can be
fertilized by B, but not B by A, quoting Gartner's case of Nico-
tiana pantculata X -^- langsdorfii in which, out of 79 flowers,
66 set fruit ; whereas, of 44 flowers of the reciprocal cross, not
one set seed. Nageli remarks (p. 196), regarding sexual affinity:

"As pertains to the latter, one knows nothing concerning the nature
of it. Possibly it might be conditioned through external (mechanical)
causes ; more probably it is connected with local chemico-physical consti-
tutions lying in the sex organs.

3. "The fertility of hybrids is so much the less, . . . the farther the
propagating forms are removed from one" another in sexual relationship.
Species-hybrids are thus, in general, less fertile than variety-hybrids."
{ib., p. 200.)

4. "The rule that the sexual affinity is so much the greater the nearer
the parental forms are externally and internally related holds good only
up to a certain limit, within which the fertility diminishes in both re-
spects." {ib., p. 207.)

The closer the sexual affinity, the easier cross-fertilization oc-

i88 PLANT HYBRIDIZATION BEFORE MENDEL

curs, the more seeds are produced, and the hybrids springing from
them are the more fertile up to a certain limit, self-fertilization
producing, as a rule, plants with less fertility and vegetative vigor
than cross-fertilization with a nearly related variety. Crossing
within the same variety is, for the most part, less favorable than
crossing with a nearly related variety.

5. "If at the same time different kinds of pollen get upon the stigma,
only that one becomes operative which has the greater sexual affinity."
{lb., p. 210.)

When two kinds of pollen reach the stigma, the one alone is
effective that has the greater sexual affinity. Consequently, the
presence of pollen of the same species excludes as a rule the
possibility of hybrid fertilization through another species. Since
fertilization through pollen of weaker affinity takes place more
slowly, therefore pollen of stronger affinity which arrives some-
what later may function likewise, and seeds of two kinds be pro-
duced in one plant.

6. "The peculiar operation of the male material affects exclusively
the germinal vesicle fertilized by it, and makes itself manifest therefore
only in the embryo, and in the plant grown out of it." {ib., p. 213.)

The operation of the male fertilizing material affects only the
embryo-sac, and makes itself evident only in the embryo and the
plant growing therefrom. The later changes are the same, no
matter what the source of the pollen may be. (ib.)

7. "The hybrid sprung from the commingling of two different parental
forms stands between the two in its systematic characters. For the most
part, it holds about the middle position ; more seldom, it has received
from one of them a preponderating share, so that it resembles the one
parental form more than the other." {ib., p. 214.)

A cross arising from two different parental forms stands be-
tween them in respect to the systematic characters, generally more
or less in the middle ; more seldom one or the other parent has a
preponderant share, so that it resembles it more than the other
parental form ; this being more strikingly evident in variety- than
in species-hybrids. In hybrid breeding, either every character oc-
cupies an intermediate position, or a part of the characters ap-
proach the one, a part the other parental form. In the latter case,
the division often occurs in such manner that the vegetative or-
gans (stems and leaves), more nearly correspond to the one, or
the reproductive (flowers and fruits), to the other. In general, the

PLANT HYBRIDIZATION BEFORE MENDEL 189

characters go over to the hybrid the more unchanged, the more
inessential they are : the more important and constant they are,
the more they are intermediate structures. For this reason, par-
ental characters in species-hybrids tend to be fused ; in variety-
hybrids to be more or less unmodified. Whether the one or the
other parental form is used as the pollen parent is of little or no
significance, so far as the characters of the hybrid are concerned.
Nageli holds, however, that the exchange of parents in reciprocal
crossing brings about a modification of inner characters in the
hybrid, which become evident in unlike fertility and in an unlike
tendency to vary in the progeny, {ib.)

8. "The rule that the characters of the hybrid plant move between the
corresponding ones of the parental forms does not hold good in a strict
sense." {ib., p. 225.)

Some characters, by virtue of individual variation, may extend
over this boundary, which happens the more, the more nearly re-
lated to each other the parental forms are ; hence, most nearly in
the case of little different varieties. The variation from the rule in
the case of species-hybrids assumes a general character, through
the fact that the hybrids of nearly related species become weakened
in the reproductive organs, but luxuriate in the vegetative organs,
and that the hybrids of more distantly related species develop
feebly in all their parts, and soon die out through lack of vital
energy, {ib.)

9. "In general, hybrids vary so much the less in the first generation,
the farther the parental forms are removed from one another in re-
lationship ; thus species-hybrids less than variety-hybrids. The former
are often distinguished by great uniformity, the latter by great diversity."
{ib., p. 230.)

If the hybrids are self-fertilized, the variability increases in the
second and succeeding generations by so much the more, the more
completely it was lacking in the first. The farther apart the paren-
tal forms lie, the more certainly the offspring in the second and suc-
ceeding generations fall into the three-. distinct varieties, one which
corresponds to the original type, and two others which are more
similar to the parental forms (Stammformen). These varieties
have, however, at least in the next generation, little constancy;
they change easily into one another. An actual reversion to one
of the two parent forms (on pure in-breeding) occurs especially
when the parental forms are very nearly related; thus with the

190 PLANT HYBRIDIZATION BEFORE MENDEL

hybrids of varieties, and of variety-like species. When it occurs
with other species-hybrids, it appears to be limited to those cases
where one species has exercised a predominant influence in the
hybrid fertilization, {ib.^ p. 231.)

Regarding "variability" in hybrids in general, Nageli remarks :

"Variability of the hybrids, that is to say, the diversity of forms which
belong to the same generation, and their behavior on propagation once
or many times by self-fertilization, form two points in the study of
hybridization which are still least ascertained, and which the least ap-
pear to be subjected to fast rules." {ib., p. 231.)

"Among the species-hybrids, there are also some which already in the
first generation show a noticeable variability. These are especially those
which are derived from very nearly related species, as the hybrid of
Lychnis diurna Sibth. X Lychnis vespertina Sibth. The least variability is
found as a rule in the hybrids of those parent species which possess a
slender mutual relationship." {ib., p. 232.)

In the case of allied species, each of which has similar variety
types, according to Nageli, the mutually similar types cross more
readily than the others ; e.g., Verbascum blattaria Linn, and Ver-
bascum lychnitis Linn, have both yellow and white-flowered vari-
eties. The white-flowered V. blattaria crosses more readily with
the white-flowered V. lychnitis^ and vice-versa, and the same holds
good as to the number of hybrid seeds produced.

The following statement appears to be the nearest approach
to an observation of anything like a "Mendelian" character to be
found in Niigeli's writings:

"when the hybrids are self-fertilized, the variability increases so much
the more in the second and succeeding generations, the more it was lack-
ing in the first, and indeed the farther apart the parental forms lie from
one another, the more certainly three different varieties spring up, one
which corresponds to the original [i.e., hybrid] type, and the two others
which are more like the parental forms." {ib., p. 230.)

Despite the existence of correspondence between Mendel and
Nageli, the latter does not so much as mention Mendel's Hiera-
cium crosses, even in the somewhat extensive paper of twenty-
nine pages, of March 10, 1866, "Die systematische Behandlung
der Hieracien, riicksichtlich der Mittelformen" (4h).

A further epitomization of rules or conclusions regarding hy-
brids appears, in the form of seven summarized statements and
commentaries thereupon, in Nageli's paper (4f).

1. Nageli concludes that the hybrid in all its parts is an en-
tirely normal phenomenon, and is distinguished in no manner

PLANT HYBRIDIZATION BEFORE MENDEL 191

from all other plants. A plant can thus not be distinguished imme-
diately as being of hybrid origin.

2. Since species-hybrids are frequently fertile, and the indi-
viduals of pure species not seldom infertile, the perfect or im-
perfect structure of the sex-organs is not decisive concerning the
nature of an organism. From the sterility of the male and female
organs, nothing can thus be summarily concluded regarding hy-
bridity, or from the fertility of the same regarding their pure
origin.

3. Hybrids constitute a regular intermediate formation, since
they have inherited their characters from the two parental species
in almost equal measure. An extension beyond this occurs only in
a very limited and quite definite manner.

Since the capacity for sexual reproduction becomes weakened,
and the vegetative activities especially aroused, he therefore con-
cludes :

"We can hence take a plant into consideration as a hybrid, only when
its systematic characters can respond to these demands." (p. 300.)

The total point of view regarding the hybrid, as Nageli con-
siders it to be, is even more definitely summarized in the next
succeeding sentence.

"When it is a question of the hybrid nature of a plant, the first and
most important criterion is that it be a middle form between two definite
species. This requirement is often left out of consideration."

And again :

"For the correct estimation of hybrids, it is especially to be remem-
bered that the most constant and important characters hold most ex-
actly the mean between the parent species, and that, on the other hand,
a character can so much the more approach the one species, the more
unimportant it is." (4f, p. 300.)

4. Between two forms there exists only one hybrid middle
form, indifferently whichever of the parental forms was used as
the pollen parent. On the other hand, the hybrid may form vari-
eties, which approach the parents in- an irregular manner.

5. Hybrid fertilization takes place through foreign pollen,
when its own pollen is kept away from the stigma.

6. Species-hybrids have, as a rule, either quite infertile or
weakened reproductive organs. In the latter case they form, on
self-fertilization, a limited number of viable seeds, and die out
after a few or several generations.

192 PLANT HYBRIDIZATION BEFORE MENDEL

Pollination through one of the two parent species, however,
excludes self-fertilization, and the hybrid reverts back to this
parental species. The hybrid middle-forms between species have
accordingly no constancy, and disappear again after a short time.
According to the relationship of the parental forms, they appear
in three ways :

(i) In the species with the most limited relationship: as a
middle-form, present in an extremely few quite infertile indi-
viduals, without transition-forms to the parental species.

(2) In species with limited relationship: as a scanty middle-
form with restricted fertility, and with individual transition-
forms to one or the other of the two parent species.

(3) In species with close relationship: as a more or less scanty
middle-form with partial fertility, and with numerous transition-
forms to both the parent species.

7. There are other intermediate forms, which are distinguished
through greater individual numbers, and through complete fer-
tility and constancy. They appear in three ways :

(1) As an isolated middle-form; the gaps between it and the
two principal species being mostly tilled up by scanty hybrid
transition-forms.

(2) As two or several isolated middle-forms which lead by
degrees from one principal species to another ; the gaps between
these and between them and the principal forms being filled up
through limited hybrid transition stages.

(3) An unnoticeable transition series between the two principal
species, in which all the members are represented by numerous
and completely fertile individuals. The hybridity of these con-
stant intermediate forms is apparently evidenced by their occur-
rence solely in company with the parental forms.

In one passage (4c, p. 229), Nageli remarks upon the fact of
heterosis in species-hybrids, i.e., the fact that species-hybrids show,
in the whole vegetative sphere in the widest sense,

"... a striking tendency to vegetative luxuriance ; in this respect they
ordinarily transcend the two parental varieties."

A statement of a rather general character regarding species-
crosses is made as follows (4e, p. 260) :

"when two species together form a hybrid, the characters in which
the parents differ from one another do not go over to it complete, but

PLANT HYBRIDIZATION BEFORE MENDEL 193

they are united to form intermediate characters, which are only incom-
pletely accommodated."

Farther on (p. 263), he comments on the fact that two hybrid-
izing forms, because they furnish each a single fertilizing cell,
share, equally in the hybrid product. It is not assumed, he says,
that two different plants have their reproductive cells qualita-
tively and quantitatively similarly fitted out, but it may be as-
sumed on the contrary, that the reproductive cells of different
species, varieties, and individuals, are always dissimilarly consti-
tuted, and that hence that plant which forms the active material
in greatest quantity and of best quality has always the preponder-
ance in the fertilization.

The discussion of the nature of the hybrid in "Die Theorie der
Bastardbildung" (4e) is further to be summarized as follows :

Two species of different genera, or of different sections of the
same genus, do not ordinarily bring about cell division in the
embryo, the fertilization remaining without result. If the hybrid-^
izing forms are a little more nearly related, the embryo remains
few-celled and dies out. With nearer relationship, the embryo de-
velops but does not germinate ; or it germinates, but forms a very
weakly plant which soon dies, or else a weakly plant which flowers
but does not bear seed. As the relationship of the parental forms
becomes closer, the vitality of the hybrid increases, reaching its
maximum as a rule, when nearly related varieties mutually cross.
He concludes that the unlike viability of the product proceeding
from self-fertilization, in-breeding, crossing of varieties, and the
hybridization of species, respectively, is due to the greater or
lesser degree of disturbances taking place in the individual, and
the general initial adaptability of the fertilizing cells. Since vege-
tative growth and reproduction are two essentially different func-
tions, two types of mutual adaptation must be assumed, the vege-
tative and the sexual. Neither of these is complete, inasmuch as
the one partly excludes the other. The sexual harmony (Concor-
danz) is much more easily disturbed than the vegetative. Hence,
under deleterious influences, a plant usually limits, first its seed
reproduction, and long afterward its vegetative activity. The in-
fertility of a hybrid depends upon the disturbance of the sexual
adaptation, i.e., upon whether the pollen tube of the one and the
germinal vesicle of the other form a union capable of develop-

194 PLANT HYBRIDIZATION BEFORE MENDEL

ment. It is sometimes the case, that the pollen tubes of A have
a greater sexual attraction to the germinal vesicle of B, than the
pollen tubes of B to the germinal vesicle of A. Hybrids are stated
to possess one character in common, that they are much more in-
clined to variation than are the pure forms. This variability, ac-
cording to Nageli, in the case of variety-hybrids, occurs in the
first generation ; in the case of species-hybrids, in the second or
later generations. Sometimes, Nageli proceeds, the offspring re-
semble, not the parents but the grandparents, and characters
sometimes come into appearance in a later generation, which were
present in a previous generation, but which afterwards disap-
peared. The organism may, at the same time, harbor several ten-
dencies, of which some attain to development sooner, others later,
and others not at all. He continues :

"It is now comprehensible that pre-eminently two tendencies are lo-
cated in the hybrid, the one that it should resemble the father, the other
that it should resemble the mother. Correspondingly, the changes in the
second and following generations consist especially in this, that forms
develop which are very similar to the two parent forms." (p. 285.)

The tendency of cultivated plants to vary more than wild
plants may, according to Nageli, have a double cause. On the one
hand, through the long operation of partly unnatural conditions,
the balance is seriously disturbed, and hence a stimulation is
given to inner changes. More important is the circumstance that
natural selection does not take place, or only in a direction cor-
responding to the demands of cultivation. In the wild condi-
tion, the incipient new varieties perish, since, in the struggle for
existence, only the most advantageous variation persists. In cul-
tivation, on the other hand, all individual variations, so far as
they form seeds and do not run counter to the demands of culti-
vation, reproduce and form new indi.vidual modifications through
crossing with other variations.

A physiological question discussed by Nageli, is that of the
relative infertility of species-hybrids. For example, according to
Gartner's experiment which Nageli cites, the hybrids between Lo-
belia cardinalis Linn, and Lobelia fulgens Willd. ripened 900
seeds per capsule; the parents, on the other hand, 1,100 to 1,200.
Lychnis-diurria Sibth. X L. vespertina Sibth. produced 90 to 125;
the parents 150 to 190 seeds. Datura stramonium X -0. tatula

PLANT HYBRIDIZATION BEFORE MENDEL 195

Linn, gave 220 to 280 seeds ; the parents 600 to 800 seeds. There
are other hybrids, as Nageli says, which produce only ^4' i/^'
1/10, or 1/20 as many seeds as the parent species. This weaken-
ing of sexual vigor in species-hybrids, as Nageli says, also

". . . shows itself plainly in the fact that all species-hybrids give fewer
seeds by self-fertilization than when pollinated by one of the parent
species." (4c, p. 202.)

A question of scientific moment, is discussed by Nageli in re-
spect to the nature of reciprocal crosses. In most of Kolreuter's
and Gartner's crosses, as Nageli says, the results of the crosses
were so much alike that a difference in point of deviation was
not to be recognized. In the case of some plants, however, a
slight difference showed itself

". . . more frequently in the form and color of the flowers, more seldom
in the form and substance of the leaves." (4c, p. 217.)

Nageli calls attention also to the fact brought out by Gartner's
investigations, that in some cases, where reciprocal crosses are
identical, yet their progeny derived from self-fertilization show
differences. Gartner's cases are cited, of Digitalis purpurea X D.
lutea, and Dianthus pulchellus X D. arenarius, as being more
"variable" in their progeny than their reciprocals. What this par-
ticular mode of variability in the first generation may consist in
is not stated.

The general state of knowledge in Nageli's time of the be-
havior of plants in crossing, since made clear through Mendel's
results, is well exemplified in his statement as follows:

"if it is certain that in hybrid formation, in individual cases, the one
parental form shares more actively than the other, still the question may
be reasonably asked, whether the hybrid ever inherits mathematically
equally much from its parents ; whether the one or the other parental
form has not always the preponderance. This is, of course, probable,
but facts are still lacking which are able to decide the question in one
or the other direction." (4c, p. 222.)

Mendel's work solved in part this" very problem, to the extent
of showing the presence of so-called "dominant" factors in the
one or the other parent. Nageli's paper (4b), here reviewed, was
read before the Royal Bavarian Academy of Sciences at Munich,
December 15, 1865. The preceding February 8 and March 8 of
the same year witnessed the reading of Mendel's paper on hybrid-
ization, before the Natural History Society of Briinn. In other

196 PLANT HYBRIDIZATION BEFORE MENDEL

words, less than one year before the question as to the reason for
the preponderance of one parental contribution over the other,
was siated by Nageli as lacking facts for its elucidation, Mendel
had already presented the facts explaining dominance,

Nageli, from the then generally existing point of view, stated
the mode of transfer of the characters in hybrids as follows :

"The characters of the parental forms are, as a rule, so carried over
to the hybrid that, in every individual one, the mutual influence makes
itself felt. One character does not go over as it were unchanged from
one, the other unchanged from the other parental form, but there occurs
an inter-penetration of the paternal and the maternal character, and an
intimacy between their characters." (4c, p. 222.)

Here again we have a statement which has been modified by
Mendel's discovery of dominance in variety-crosses. Nageli re-
marks, however, that those who have largely or exclusively
crossed varieties, or in crosses have given their attention to
"varietal characters" so-called, are of the opinion that the char-
acters go over unchanged, quoting the results of Sageret's ex-
periments referred to in a previous article. Despite these cases of
what is now known as dominance, Nageli states the general rule
as he saw it, thus :

"The rule, however, is that the characters of the father and the mother
combine and interpenetrate, w^hereby a new individual character origi-
nates which holds more or less the mean. The way and manner in which
the union occurs cannot be determined in advance." {ib., p. 224.)

Regarding the vigor of first-generation hybrids, Nageli remarks
as follows :

"Growth and development of the individual is especially aroused in
species-hybrids. These are frequently larger than their two parents. They
form more and larger leaves, the stem is raised higher, and branches
more vigorously, and effects multiplication more easily through stolons,
rhizomes, etc. . . . Hybrids are also distinguished through the fact that
they bloom longer and more abundantly than the two parent forms.
The hybrid of plants which bloom first in the second year, blooms for
the most part in the first; the hybrid of plants which only come to
flower formation after a series of years, arrives thereat a few years
earlier. Likewise, with regard to the individual vegetative period, the
rule holds good that the hybrids begin to bloom earlier in the year and
continue to bloom later in the fall. In general, they often form quite a
large quantity of flowers, which are especially larger, sometimes also
more fragrant and intensely colored, and of which each individual one
lasts longer, for example several days ; when the flowers of the parent
species wilt after the first day." {ib., p. 228.)

This closes the account of Nageli's contribution to the literature

PLANT HYBRIDIZATION BEFORE MENDEL 197

of hybrids — a rather clear, complete,, and searching review of the
fundamental matters in respect to hybridization, as they were
realized and generally understood at that time.

In view of the considerable attention at one time aroused by
Nageli's theory of the idioplasm, and the fact that it is interesting
historically as a presentation of a theory thought to be possibly
operative in the case of amphimixis, it seems desirable to intro-
duce at this point a presentation of Nageli's contribution to the
theory of the factors in development (Mechanisch-physiologische
Theorie der /\bstammungslehre). (41, pp. 822, 1884.) It is hoped
that the historical value of the contribution, theoretically speak-
ing, as being one of the last of the unitary theories of descent
propounded before the discovery of Mendel's investigations, will
make amends for the quantity of the material necessarily intro-
duced.

Nageli considers that the substance containing the "Anlagen"
(the "Plasmasubstanz") consists of different modifications of
albumins, the molecules of which are united in molecular groups
of crystalline form, which he calls "micellae," soluble and in-
soluble forms commingled, forming a half-fluid, slime-like mass.
This organization he designates as the "stereoplasm," of which
he considers that only the smaller portion represents the actual
"Anlagen" or factors.

From what Nageli calls the "Anlage-plasm^" i.e., the gene-
protoplasm, there is a definite movement of a developmental
character, leading to a cell-complex of greater or less size, such
as a certain leaf, root, etc. This protoplasmic series Nageli desig-
nates briefly as the "idioplasm," as distinguished from the re-
maining "stereoplasm." (^i, p. 23.) Crossing, or rather amphi-
mixis, is considered to be the cause of bringing the factors of
lesser S'trength into development. Crossing especially is supposed
to be one of the causes for the development of the "Anlagen"
(factor-rudiments) of lesser potency, that is to say, those still in
process either of origination, or of disappearance. Latent Anlagen^
come more easily into development through amphimixis than
through sexual modes of propagation, (ib., p. 24.) Differences in

1 The German word "Anlagen" being practically untranslatable will
be used henceforth without further comment, for "rudiments of factors,"
etc.

198 PLANT HYBRIDIZATION BEFORE MENDEL

growth, internal organization and external conformation, as well
as in the activities of the organism, are conditioned by number-
less differences in the chemical and plastic processes of the living
material, and by numberless combinations of the operative forces,
all of which are due to "the unlike form, size and arrangement
of the micellae of the idioplasm." (p. 26.)

This being the case, then equality in respect to the inheritance,
is conditioned by the combining cells containing, on fertilization,
equal amounts of the idioplasmic material. Cases where a pre-
ponderance in the inheritance is on the side of the male or the
female parent, respectively,

". . . must be explained through the fact that a greater quantity of
idioplasm occurs, now in the unfertilized egg cells, now in the sperma-
tozoa uniting with them." (p. 27.)

The difference in potency of the idioplasm is indicated by the
fact that the male fertilization-plasma in the spermatozoid may
amount, in Nageli's view, to only one or two parts of the mass
of that of the female in the unfertilized egg cell or primordial
vesicle, and yet, if it contains an equal number of hereditary
units (Anlagen), then these must possess a hundred times more
"idioplastic power" than those of the egg. This purely empirical
mass theory of the mechanics of heredity preceded the chromo-
some explanation of the facts.

With regard to the relative total amount of the idioplasm,
Nageli holds that it is probable that only a very small part is
to be designated as the idioplasm proper, while the remainder
must be regarded as trophoplasm or nutritive plasm.

"The activity of the idioplasm makes itself everywhere evident where
an heritable process of growth or metamorphosis takes place. Its pres-
ence in these places may therefore be presumed. When, on the contrary,
there are places where neither growth nor metamorphosis can take place,
it is presumed that the cause may either be due to lack of the idioplasm
or partly to the fact that a proper mixture of idioplasm and tropho-
plasm is lacking." (p. 29.)

The idioplasm is presumed to be in a continual state of migra-
tion toward the places of development, and the growth processes
are determined, first by the constitution of the idioplasm, secondly
by its quantity, and thirdly by the manner in which it is com-
mingled with the trophoplasm. (p. 29.)

Nageli holds that either the idioplasm changes continually dur-

PLANT HYBRIDIZATION BEFORE MENDEL 199

ing the growth process, returning with the formation of the em-
bryo to its original constitution in the initial cell, or else it main-
tains the same constitution, and the altered conditions of time and
place in the individual's life-history affect its potentiality, (p. 30.)
Attention is called to the fact that a branch with different char-
acters from those of other branches, may grow out from a tree,
a case, manifestly, in which external conditions do not come into
play. In such cases, the idioplasm has evidently undergone a
phylogenetic metamorphosis, (p. 31.) It is assumed to be possible
for the idioplasm to change within definite limits, during indi-
vidual growth. The idioplasm of each of the different cells of
an individual may be considered, for practical purposes, as differ-
ent, "insofar as it possesses an individual productive capacity."
(p. 31.) The development into activity of the Anlagen in the
idioplasm is conditioned to some extent by the nutrition, e.g.,
whether, in the case of certain trees, foliage or flower shoots are
formed, or vegetative growth without flower formation at all,
under unfavorable climatic conditions, (p. 32.) The variety in
the growth processes in the idioplasm is conceived of as possible
in the following manner : The idioplasmic structure represents a
fixed arrangement, and its parts (the micellae) may be conceived
of as lying in rows in several dimensions crossing one another,
so that the same particle always belongs to rows of divergent
space-dimensions. Growth of the idioplasm is the growth of these
rows through the accession of new micellae, uniformly interca-
lated, or through end-deposition. The idioplasm may increase
either through the growth of the rows alone, through the exten-
sion in width of the cross-rows, or through the growth of rows
in some oblique direction. The growth of the rows in question to
some determined dimension results in the development of a defi-
nite "Anlage." (p. 34.) This structure of an idioplasmatic system,
Nageli holds, is analogous to that of other organized bodies,
which consists of crystalline micellae, comprising a larger or
smaller number of molecules.

"The starch grains give us a presentment of the idioplasm. Both are
fixed micellar systems, which lie free in the cell contents, in the cell-sap
or in the half-fluid plasm, and which grow through the intercalation of
micellae."

The idioplasm, constructed as surmised above, "can be known

200 PLANT HYBRIDIZATION BEFORE MENDEL

only in one dimension, namely, in that in which its autogenetic
growth takes place." However, the idioplasm in an individual
propagating vegetatively may retain its arrangement unchanged
to the smallest particular. This fact, it appears, can be explained
in no other way than by the fact of the idioplasm being ar-
ranged in firmly converging parallel rows, which grow through
micellar intercalation, the structural arrangement remaining the
same. (p. 38.)

One assumption, which as Nageli says, "is scarcely to be proved
out of hand," is that the idioplasm constitutes a connected net
throughout the entire organism.

"This will assume in the cells, according to their construction, a differ-
ent form; ordinarily, however, in the longer plant cells, forming a mem-
brane over the surface, frequently also running through the cell cavity
and especially crowded together in the nucleus." (p. 41.)

Since all the chemical and plastic processes of an heritable

nature are regulated through the idioplasmic fibrils, these must

be everywhere present throughout the different parts of the cells,

and communication must be supposed to take place between the

idioplasms located in the different parts of the organism.

"The idioplasm-net probably lies at the basis of the so frequently
recurring net-like arrangement of the plasma, and the net-like structure
of the nuclear substance." (p. 41.)

The idioplasm is conceived as originating the trophoplasm, and
thereby the non-albuminous constructive material, and determines
the form of the latter, fp. 47.) Nageli considers that the irritabil-
ity of the micellar rows of the idioplasm is not to be expressed
in terms of periods similar to those of nerve-activity, but that it
extends over a longer time — days, weeks, and months, during
which time the active idioplasm increases, fp. 47.)

Nageli considers it improbable that the growth of the micellar

row itself determines the development of the corresponding "An-

lagen," but rather that both phenomena are brought about by a

like cause.

"The effect, which the idioplasm group, engaged in active growth,
exercises upon the surrounding idioplasm, may occur in a manner simi-
lar to that exerted by the plasma of the yeast cells upon the fermenta-
tion material." (p. 48.)

The process of operation of the micellar rows of the idioplasm
Nageli considers theoretically to be as follows :

PLANT HYBRIDIZATION BEFORE MENDEL 201

The ontogenetic development of the individual begins, during
which time the micellar rows in the idioplasm which cause the
first developmental stage become active. This induces a passive
growth of the other rows, and an increase, perhaps manifold, of
the entire idioplasm. A tension arises from inequality in the
growth-intensities of the different rows, which sooner or later,
according to the number, arrangement, and energy of the active
rows, brings the process to a standstill ; the tension is felt as a
stimulus due to disturbance of equilibrium, and this tension is
shifted from one group of Anlagen to another, until all are passed
through, and the ontogenetic development arrives again at the
original embryonal state, during the reproductive period, (p. 40.)

The effect of nutrition upon the idioplasm is interpreted by
Nageli as follows :

The nutritional, stimuli, generally speaking, although they do
not alter the idioplasm qualitatively, may still affect the develop-
ment of the Anlagen, so that Anlagen which might otherwise re-
main latent now come into development, or, the nutrition being
lacking, their development is checked.

Nageli considers it possible that the idioplasm may only return
approximately, during the reproduction stage, to its original con-
stitution, and that a slow phylogenetic metamorphosis may take
place, fp. 53.) It is manifest, as he says, that, in order for this
to occur, the external influences must either directly or indirectly
bring about a metamorphosis of the idioplasm, (p. 54.) In order
for the idioplasm undergoing change in some specific part of the
organism to bring about alterations in the rest, the result must
be achieved in either a material or a dynamic way. By the former
method, Nageli conceives it possible that all the cells communi-
cate with one another and with the nearest sieve tubes by means
of very fine pores.

"The sieve-tubes, however, which represent large canals with laterally-
large openings in the uninterrupted partition-walls, bring about the ex-
change between the most different and distant organs." (p. 56.)

According to the dynamic theory, if all plant cells communi-
cated with one another through fine pores, then these pores con-
tain, besides the trophoplasm, also idioplasm, "so that the latter
forms a connecting system through the whole organism." The
net-like connection then of the idioplasm throughout the organ-

202 PLANT HYBRIDIZATION BEFORE MENDEL

ism, from cell to cell through the pore-canals, makes possible the
transfer of stimuli in a manner analogous to that of the nerves,
(p. 58.) For transmission to a distant point in the organism,

". . . there requires to be not merely a single stimulus, but rather a sum
of various stimuli to be transmitted, which are able to cause a qualita-
tively definite process."

This sense-image conduction through the idioplasm is conceived
of as being brought about by organized albuminous bodies.

"This theory of dynamic participation appears to me to solve the
question at hand in the simplest manner. The idioplasm of all the cells
of a plant exists in immediate contact. Every change which it experiences
in any place becomes everywhere recognized, and in a corresponding
manner utilized. We must assume that the stimulus that operates locally
is immediately telegraphed everywhere, and everywhere has the same
effect; for everywhere a continuous and general sensation which the
idioplasm experiences explains the otherwise impressive fact, that the
idioplasm, despite the so dissimilar conditions of nutrition and stimulus
to which it is exposed in the different parts of an organism, yet develops
and changes everywhere in completely like manner, as we especially
recognize from the fact that the cells of the root, the stem, and the leaf,
produce exactly the same individual."

Nageli now constructs a theory of sex development as follows:
A peculiar category of Anlagen may occupy a middle place
between stability and instability, formed by the cohesion of two
or more Anlagen, of which one must develop to the exclusion of
the other. This will depend now upon internal and now upon
external causes.

"Thus, doubtless, it is inner, but still unknown causes which, in the
case of organisms in which the sexes are separate, determine whether,
in a developing embryo, the male or female organism reaches develop-
ment." (p. 194.)

We thus have a purely theoretical conception of sex-equilibrium
as existing in the groups of Anlagen in the idioplasm, of which
external causes of some sort stimulate the development of some
rather than that of their partners in the equilibrium.

Nageli emphasizes the conception that the increase of the idio-
plasm in ontogenetic development takes place

". . . through the longitudinal growth of the rows, namely, through
intercalary insertion of micellae in every micellar row, which thereby
elongates, without altering their cross-sectional configuration." (p. 531.)

Each row, therefore, is considered to contain all the Anlagen
which the individual has inherited in the embryo, and each cell

PLANT HYBRIDIZATION BEFORE MENDEL 203

accordingly is entire in respect to its idioplasmic content, and is
idioplasmatically capacitated to become the germ of a new indi-
vidual, (p. 531.)

The evolution process, from the standpoint of the idioplasm,
is depicted by Nageli in the following manner :

"The idioplasm through accretion [mit der Zunahme] steadily changes
its configuration in the successive ontogenies, but relatively slowly ; so that
from the embryo of one generation to the embryo of the next genera-
tion it makes a small amount of progress. The summation of these
progress-differentials through a whole line of descent represents the
genetic history of an organism, since the latter through its idioplasm
alone holds together in unbroken continuity with the unicellular be-
ginning of the stock." (p. 532.)

"since further, in embryo-formation, the new ontogeny begins as a
unicellular individual, so that the Anlagen of the idioplasm come into
development which have arisen in the unicellular ancestor, and simi-
larly the successively following development of the Anlagen which have
their origin in their analogous ancestors, the two cooperating causes, the
phylogenetic configuration of the idioplasm successively following, and
the developmental stages of the individual conditioned by these, have,
as a necessary consequence, that the ontogeny is the recapitulation of
the phylogeny." (p. 533.)

In the idioplasm of an embryo, the micellar rows of Anlagen
from the respective parents may in some cases, Nageli holds, have
a medium composition, due apparently to the merging of the
micellar rows of the two parents. In such cases, intermediate
characters will develop. Or, on the other hand,

"The paternal and maternal rows lie unaltered in the idioplasm of the
child, and in different grouping in relation to one another, and bring
about in the organism the characters from the two sides, either unmodi-
fied beside one another, or only one of the parental characters, while the
other remains latent." (p. 534.)

The relative development or latency of the inherited Anlagen
in the child determines the degree of resemblance to the one or
the other parent. The theory of descent, then, is concisely stated
by Nageli as follows :

"since from one ontogeny to the next following, idioplasm alone
is carried over, therefore the phylogenetic development consists only
of the continuous formation of the idioplasm, and the entire pedigree,
from the primordial drop of plasma to the now living organism (plant
or animal), is really nothing else than an individual consisting of idio-
plasm, which in every ontogeny, forms a new individual body corre-
sponding to its progress." (p. 541.)

"of heredity as a specific phenomenon, if we hold the internal essence
of the organisms in view, there can really be no discussion, since the

204 PLANT HYBRIDIZATION BEFORE MENDEL

line of descent is a continuous individual of idioplasm. In this case it is
nothing but the persistence of the organized substance in a changing
process of movement or the necessary passing over of one idioplasmatic
configuration into the next following. And it is not alone between the
ontogenetically different plant- and animal-individuals, but also within
these individuals everywhere present, where every individual part (cells,
organs) follows another in time. Heritable phenomena are such as of
necessity pass over to the following generations, and in general such as
have their seat in the idioplasm, since the non-idioplasmic substance is
only capable of continuing through a limited number of cell genera-
tions." (p. 542.)

27. Treatise of W. O. Focke.

The last of the hybridists of the older school who engaged in
extensive publication, was Wilhelm Olbers Focke, who published
in 1881, his 'Tflanzenmischlinge," a work of 569 pages (1), con-
sisting primarily of a systematic arrangement, according to or-
ders, families, and genera, of plant hybrids known to have been
produced by various experimenters up to his time, or reported
as having been found wild. This arrangement, while it made no
pretension to completeness, was yet the most thorough and exten-
sive single compendium of the kind yet published.

"I have," he says, "so far as it was possible, examined the statements
met with, have not quoted the least credible at all ; others I have ac-
cepted as questionable, but, in the case of the most of the information,
I have had no reason for doubting the correctness of the observations,
even though, on the other hand, I could not regard them as confirmed
or sufficiently vouched for." (p. 3.)

"At all events," Focke remarks, "through the present collection of
known facts, it will, as I think, be rendered essentially easier to find
the objects toward which future investigations concerning plant crosses
must be directed." {ib., p. 2.)

In the case of most hybrids, especially those occurring wild,
Focke contented himself with brief references concerning their
occurrence, but entered into more extended consideration of the
more carefully investigated hybrids produced by hand-pollina-
tion.

Focke himself was not extensively engaged in investigations in
hybridization.

"To my regret," he says, "l have never been in a situation to institute
hybridization experiments on a large scale, nevertheless, through crosses
and breeding carried on by myself, I have at least gained some practical
experience, which should be of decided use for the estimation of the
statements of others." {ih., p. 3.)

As to the results of his observations however, Focke came to

PLANT HYBRIDIZATION BEFORE MENDEL 205

an important generalization regarding the size of F^ hybrids;
that the characters of crosses are derived from the characters of
the parent species ; and that only in size and luxuriance^ as well

i^'j^nih .v.Y.Y. ii. W. O. Focke, d. 1922.

206

PLANT HYBRIDIZATION BEFORE MENDEL

as in sexual capacity^ are hybrids for the most part distinguished
from the two parental species.

Crosses between different races and species are distinguished
from individuals of a pure race by their vegetative activity.

Hybrids between markedly different races, he remarks, are fre-
quently very tender, especially in youth, so that the rearing of the
seedlings takes place with difficulty. Hybrids between more nearly
related species and races^ on the other hand^ are as a rule thrifty
and vigorous; they are distinguished for the most part by size,
rapidity of growth, early flowering, abundance of bloom, long
duration of life, marked capacity of reproduction, unusual size of
individual organs and similar characteristics.

"Complete reversions to the parental types, without the operation of
the pollen of the parents, occur only in the case of the hybrids of nearly
related races."

Focke's own experiments were made in the crossing of species
of Raphanus, Melandryum, Rubus, Anagallis, Digitalis, and Nico-
tiana. While the actual number of crosses made by Focke was
few, and the results, as in the case of most other observers of
hybrid phenomena, were not analyzed in respect to the generations
of the hybrids, yet in the one case of a cross made between Digi-
talis purpurea X ^« ambigua Focke made measurements of cer-
tain organs in the parents and in the hybrids, which, so far as
the writer's inquiry has extended, with the exception of those of

Upper calyx
apex

Remaining
calyx apex

Length of
the corolla

upper lower

Width
of the
corolla

Height
of the
corolla

length width
(mm.) (mm.)

Digitalis
purpurea

22 4

22 10

44 54

Digitalis
ambigua

9 1-5

11 2

31 40

Digitalis
purpurea

X
ambigua

i8 3

20 5

38 45

Summary of Averages

Average of length measurements, assuming a mean

condition to be the normal
Average of width measurements

Theoretical Found

mm.

26.3
9-6

mm.

23.0

7.0

PLANT HYBRIDIZATION BEFORE MENDEL 207

Darwin and Mendel, and the single experiments of Henslow, also
with Digitalis^ and of MacFarlane with a number of other species,
constitute the only quantitative measurements made upon hybrid
cases prior to 1900. The data are few, but are historically inter-
esting. They show the intermediate condition in the F^ generation
in respect to length and width of the organs measured, (p. 320.)
By Focke's time (1881) the details regarding the behavior of
hybrids had sufficiently accumulated so that he was able to say :

"Our knowledge concerning the fertilization of plants has noticeably-
extended during recent decades, so that we are no longer in a position
to group the facts together, as has been customary, under a few general
standpoints. The multifariousness of the phenomena in organic nature is
enormously greater than one has thus far been accustomed to assume."
(p. 446.)

Focke had distinctly the physiological rather than the morpho-
logical point of view regarding hybrids and hybridization, and
was not bound by wooden or stereotyped conventions of thought
regarding the systematic relations of species.

"Taken as a whole, it is correct, that the groups of forms do not as a
rule very well admit of being delimited according to their sexual be-
havior. The degrees of morphological and physiological differences cor-
respond to one another frequently somewhat exactly, yet there are ex-
amples in which this is absolutely not the case." (p. 448.)

Again he expresses a plastic point of view in this regard, in
the following words :

"One will do well not to judge the morphological relations between
two plant forms according to their physiological behavior and vice versa.
It is a question in every case of- determining the facts, but not to force
them into a definite mould.

"Under all circumstances, from the beha'vior of hybrids, one may only
with great care be able to draw conclusions concerning the specific like-
ness or unlikeness of the parental forms." (p. 449.)

The fact that, as a rule, the nearer the systematic relationship
becomes, the more readily what are called "species" cross, was
naturally sufficiently recognized by Focke.

"Two essentially different species can scarcely ever completely mu-
tually fertilize each other." (p. 457.)

"Many hybrids, especially those between unlike parent species, are, as
stated, unfruitful ; the most show a diminished, a few an almost normal
fertility." (p. 457.)

"A delimitation of genera in such a manner that all species which are
able to furnish hybrids among one another may be placed in the same
genus, would be extremely unnatural. On the other hand, it is not far-

2o8 PLANT HYBRIDIZATION BEFORE MENDEL

fetched to think of limiting the boundary of a genus to species which
are capable of mutual fertilization." (p. 456.)

"We may therefore assert the rule that the races of one and the same
species, or of very nearly related species, almost always are capable of
mutual fertilization without special difficulty." (p. 450.)

Focke calls attention to the interesting fact that different

families and different genera are very unlike in respect to their

capacity for cross-fertilization.

"In some families, individual genera show very great differences in
their tendency to and their capacity of hybridization." (p. 451.)

However, "whether two species may be crossed with one another or not,
can only be determined with certainty through experiment." (p. 451.)

Focke calls attention to the matter of ecological species in rela-
tion to crossing, that deserves much further investigation.

"It appears to be difficult to cross plants with one another, which in-
habit very different zones, or very different habitats (water and dry
places). When it succeeds, the hybrids are sterile." (p. 453.)

However, he calls attention to the fact that :

"The origin of plants from the old or the new world, from the north-
ern or the southern hemisphere, forms in and for itself no hindrance to
crossing. Evergreens and deciduous, day-blooming and night-blooming
plants may often cross without difficulty." (p. 454.)

"In some genera or groups of species, in which hybrids easily origi-
nate, there are individual species which appear to be more inclined than
others to enter into hybrid combinations." (p. 454.)

Focke calls attention to the fact that hybrid formation between
two species does not always succeed equally easily in both direc-
tions, mentioning the case of Mirabilis jalapa X M. longifiora :

"Many other cases are furnished by breeders of hybrids, in which
hybridization has succeeded in only one way. if, however, the experiments
have not been carried on frequently and in various places, and with
different individuals and races of the parents, one can draw no far-
reaching conclusions from the failure." (p. 455.)

"it has not seldom been observed that two species are mutually able to
effectively pollinate each other, but that A produces more seeds with the
pollen of B, then B with the pollen of A." (p. 455.)

According to Focke,

". . . most of these cases come from Gartner's experience, and require
still further confirmation, if indeed the occurrence of this relation may
not be completely questioned." (p. 455.)

Focke calls attention to an impression he had gained:

"That genera with more or less zygomorphic flowers, which belong to
families in which actinomorphy prevails, show quite an especial inclina-
tion toward hybrid formation.

"whoever is not able to recognize immediately from his own observa-
tion the fluidity and mutability of the series of living forms, a few

PLANT HYBRIDIZATION BEFORE MENDEL 209

newly-described intermediate forms will certainly not convince him of
the correctness of the doctrine of descent. The more earnestly and care-
fully one proceeds in the exploration of truth, so much the more gain
will science and the theory of evolution derive from the investigation."

(p. 463-)

Focke disposes of the question whether a plant pollinated from
two sources could produce double-pollinated seeds, in the follow-
ing words :

"By analogy with animal fertilization-phenomena, it is to be regarded
as unquestionable, that every single ovule can only be fertilized by a
single pollen tube. It is a fact that, in all experiments carried out with
scientific precision, no hybrid has ever been obtained, in which the
operation of more than one parental species was to be recognized, no
matter how many kinds of pollen might be placed upon the stigmas of
the maternal flowers." (p. 448.)

On the basis of the available data, Focke undertook to formu-
late a series of statements or rules, embodying the laws of the
behavior of hybrids so far as the then existing information made
it possible to do so. This was the first direct attempt after Nageli,
among the hybridizers of the older school, to formulate a com-
plete, coherent statement of principles from the extensive body of
data connected with hybridization. The five laws or principles
which Focke laid down are as follows :

1. "All individuals derived from the crossing of two pure species or
races are, when produced and grown under like conditions, as a rule
completely alike, or are scarcely more different from one another than
specimens of one and the same pure species are accustomed to he."
(p. 469.)

As corollary to this statement, the following is appended:

"Least difficult to answer is the question, concerning which it has been
most strenuously contended, namely, that of the greater influence of
the one or the other sex on the type of the progeny. The hybrids of the
two species or races, A and B, are like each other, indifferently whether
A was the male or the female parent-species in the cross. ... It is deter-
mined through numerous experiments rather that in the plant kingdom
in general, in the case of true species, the form-determining power of
the male and the female elements in the cross are completely like one
another." (pp. 469-70.)

Focke modified this statement, however, by saying that :

"Like all other rules of hybridization, so likewise is that of the simi-
larity of both products of crossing not without exceptions. It is never-
theless self-evident that a perchance observed dissimilarity can be re-
garded as conditioned by the stronger operation of the male or the fe-
male element only when the experiments have been instituted in like
manner, and when they, by several times repetition, have always led to
the same result." (p. 470.)

210 PLANT HYBRIDIZATION BEFORE MENDEL

2. ''The characters of hybrids are derived from the characters of the
parents. Only in size and luxuriance, as in sexual power, are they dis-
distinguished for the most part from both parents!' (p. 473.)

With regard to the manner in which the characters are bound

together in hybrids, Focke makes the following statement :

"In general a fusion or mutual penetration of the characters takes
place, frequently, however, in such manner that in one aspect the one, in
another the second parental form appears to prevail. Sometimes, for ex-
ample, the hybrid recalls in its leaves more the one, in its flowers more
the other parental form." (p. 473.)

Focke remarks upon the fact that in the crossing of nearly re-
lated races, especially color-varieties, plants frequently are de-
rived, which resemble exactly or nearly so one of the parent races;
citing cases of Brassica rapa^ Linum^ Pisurn, Phaseolus, A/iagalHs,
Atropa, and Datura.

"Only in the second generation," he says, "does the influence of the
older parental race ordinarily betray itself, and in this manner that a
part of the seedlings completely or in certain respects revert to it."

(P- 474-)

"in later generations of the hybrid plants deviations from the char-
acters of the parents are still more generally observed." (p. 474.)

3. "Crosses betzueen different races and species are distinguished, as a
rule, through their vegetative activity, from the specimens of a pure
race. Hybrids between noticeably different species are frequently very
tender, especially in youth, so that the rearing of the seedlings succeeds
with difficulty. Hybrids between nearly related species and races are, on
the other hand, luxuriant and vigorous; they are distinguished for the
most part by size, rapidity of growth, early flowering, abundance of
flowers, longer life period, vigorous power of reproduction, unusual size
of individual organs, and similar characters." (p. 475.)

4. "Hybrids of different species form, in their anthers a more limited
number of pollen grains, and in their fruits a more limited number of
normal seeds than the plants of pure origin. Frequently they produce
neither pollen noir seeds. With hybrids of nearly related races this weak-
ening of the capacity for sexual reproduction as a rule is not present.
The flowers of the infertile or little fertile hybrids remain fresh as a
rule for a long time." (pp. 476-7.)

5. "Abnormalities and structural variations in the flower-parts of hy-
brid plants are far more abundant, especially, than on individuals of
pure origin." (p. 481.)

Focke's treatise is often referred to as being noteworthy for

containing, with the sole exception of Hoffman's memoir (3), the

only references to Mendel's work anterior to 1900. A. careful

study of Focke's report brings into interesting relief the reason

for his having failed to appraise the Mendel paper at its present

value. In the first place, Focke was especially interested in the

works of those who produced more extended contributions. The

PLANT HYBRIDIZATION BEFORE MENDEL 211

works of Kolreuter, Gartner, Wichura, and Wiegmann, whose
works were much more voluminous and pretentious in the field
which they occupied, receive appropriate consideration, as do
also Naudin's and Godron's prize contributions : but Mendel's
paper evidently appeared to F'ocke simply in the guise of one of
the numerous, apparently similar, contributions to the knowledge
of the results of crossing within some single group. The works
of Kolreuter and Gartner, for example, are regarded simply and
without question as attempts to compass the sphere of hybridiza-
tion phenomena as a whole, and from a much broader standpoint.
It was supposedly not at all conceivable, that the laws of hybrid
breeding could be compassed within a series of experiments upon
a single plant. Whatever experiments Mendel therefore reported
were to be considered, like the experiments of Knight and others,
merely for whatever obvious data they seemed conspicuously to
present. Focke's work is, however, an excellent compendium of
all the experiments in crossing done up to 1881. The details of
his data are laborious, exact, well classified and scientifically
arranged, comprising 79 families of Dicotyledons, 13 families of
Monocotyledons, 2 families of Gymnosperms, 2 of Pteridophytes,
1 of the Musci, and 1 of the Algae.

It is interesting, in view of the fact that Focke's publication con-
stitutes the only actual epitome, in cyclopaedic form, of the hybrid-
ization experiments carried on up to his time, to note the relative
number of references to the different more important names, as
follows: Gartner, 409; Kolreuter, 214; Herbert, 155; Godron,
102; Naudin, 89 ; Darwin, 34; Knight, 32; Caspary, 31; Wieg-
mann, 30; Nageli, 28; Lecoq, 26; Wichura, 20; Linnaeus, 21;
Mendel, 1^; Hoffmann, 14; Sageret, 10; Shirreff, 3; Rimpau, 2;
Seton and Goss, 1 each.

The fifteen references to Mendel's name occur on the following
pages and in the following connections :

Pisum

1 citation

111

Phaseolus

1 citation

215

Hier actum

2 citations

216

Hieracium

1 citation

218

Hieracium

5 citations

483

Hieracium

1 citation

444

Phaseolus and

Hieracium

1 citation

459

Theoretical

matter

1 citation

492

Theoretical

matter

1 citation

212 PLANT HYBRIDIZATION BEFORE MENDEL

The most important reference to Mendel in the above is the

often-cited remark under the genus Pisum :

"Mendel's numerous crossings gave results which were quite similar
to those of Knight, but Mendel believed that he found constant number-
relationships between the types of the crosses." (p. no.)

This Statement manifestly shows a merely superficial under-
standing of the real significance of Mendel's results. How far
short this understanding actually fell is revealed in the statement
immediately following:

"In general, the seeds produced through a hybrid pollination preserve
also, with peas, exactly the color which belongs to the mother plant,
even when from these seeds themselves plants proceed, which entirely
resemble the father plant, and which then also bring forth the seeds of
the latter." (p. iio.)

The facts of dominance, and of the difference in the significance
of cotyledon-color and seed-coat color, pass unnoticed. We have
here plainly the case of the inheritance of seed-coat color taken
for the entire case of seed-inheritance in peas, the dominance of
roundness of form discovered by Mendel being clearly overlooked.

The next reference is to crossing in Phaseolus.

"ph. vulgaris L. var nanus L. ? X multiflorus Lam. fl. coccin. $ was
produced artificially by Mendel." (p. ill.)

Then follows a paragraph of fourteen lines, discussing in a
merely conventional manner the inconclusive results of the cross,
the color-characters of flowers and seeds alone being noticed.

Mendel's statement with regard to his Phaseolus crosses fBate-

son, p. 367) was evidently overlooked, to the effect that "the

development of the hybrids, with regard to those characters which

concern the form of the plants, follows the same laws as in

Pisum,'' as well as his further suggestion regarding the matter of

color-inheritance in the plant, as follows (p. 3^7) '•

"Even these enigmatical results, however, might probably be explained
by the law governing Pisum, if we might assume that the color of the
flowers and seeds of Ph. multiflorus is a combination of two or more en-
tirely independent colors, which individually act like any other constant
character in the plant,"

the matter being then discussed analytically at length in Mendel's
characteristic form of presentation.

It seems singular that the peculiarity of Mendel's form of state-
ment, and its apparent significance, should have been able to
escape Focke's attention.

PLANT HYBRIDIZATION BEFORE MENDEL 213

The remaining passages in which Mendel is referred to, under
the discussion of Hieracium (pp. 215, 216, 218, and 483) are as
follows :

"That hybrids in this genus \Hieraciuin\ are very frequent, is certain;
individually, however, many of the views thus far are to be regarded
as not sufficiently assured. The hybrids are, according to Mendel's re-
sults, polymorphous, but the individual forms as a rule are true from
seed [pflegen samenbestandig zu sein]." (p. 215.)

"//. auricula L. $ X pilosella L. ^ was artificially produced by Fr.
Schultz and G. Mendel." (p. 215.)

"Mendel obtained only a single specimen from his artificial cross,
H. auric. $ X pilos. $ , which was somewhat fertile and furnished a
constant progeny." (p. 216.)

"G. Mendel produced //. auric. 9 yC H. prat. $ artificially : he ob-
tained 3 specimens, which were markedly different among themselves,
and were tolerably fertile ; the progeny of each of these cases resembled
the mother plant." (p. 218.)

"Mendel obtained H. auricul. 9 X aurantiacum $ , in two materially
different specimens, of which one (per-aurant.) was sterile, the other
(per-auricula.) produced a single seed." (p. 218.)

"H. praealtum Vill. $ X aurantiacum L. ^ was obtained by G. Men-
del in two different tolerably fertile specimens. The progeny of each of
these individuals resembled the mother plant; however, an individual
of the second generation had attained completely normal fertility."
(p. 218.)

"H. echioides Linn. $ X aurantiacum Linn. ^ G. Mendel obtained
in a single specimen, which was completely fertile and true to seed, and
even on pollination with the parent pollen furnished no reversions."
(p. 218.)

"//. praealtum Vill. $ X fiagellare Rchd. $ G. Mendel obtained in a
single specimen, whose fertility was nearly normal, and whose progeny
was constant." (p. 218.)

"The different primary forms of the Hieracium hybrids Mendel found
true from seed." (p. 483.)

A general statement on p. 444 shows clearly the relative unim-
portance of Mendel to Focke's mind, the name being merely that
of a person who had made certain experiments calling for men-
tion. It will be noted that the peas experiments are not alluded
to at all in Focke's general discussion ("Geschichte der Bastard-
kunde," 1, pp. 429-45), but merely those with Phaseolus and
Hieracium^ as follows :

"of the scientific crossing experiments from the most recent time, Rob.
Caspary's hybridizations of Nymphaeaceae, G. Mendel's with Phaseolus
and Hieracium, D. A. Godron's with Datura, Aegilops X Triticuin, and
Papaver, deserve to be designated as particularly instructive. Godron's
series of experiments with Datura crosses are to be regarded as the most
signal work [als die hervorragendste Leistung]." (1, p. 444.)

214 PLANT HYBRIDIZATION BEFORE MENDEL

We thus have here, succinctly expressed, the relative point of
view held by this tolerably keen scrutinizer of the literature on
hybridization up to 1881. It is evident that "G. Mendel's" investi-
gations, made very little impression upon the mind of the re-
viewer.

A further reference to Mendel's name among others appears on
p. 459, as follows :

"The experiments of Kolreuter, Wiegmann, Gartner, Godron, Naudin,
Wichura, Mendel, Caspary, and others, served only scientific ends, while
Herbert and Regel united scientific and horticultural ones." {ib., p. 459.)

The point of view expressed above is sufficiently evident. The
final reference to Mendel is on p. 492, as follows :

"To none of the scientific hybrid breeders has it occurred to attach
particular species names to his newly-produced plant forms ; Kolreuter
and Gartner, Wiegmann and Lehmann, Naudin and Godron, Wichura,
Mendel and Caspary, in this respect have proceeded quite uniformly."

We thus have, in closing, final testimony as to the merely for-
mal and conventional impression which Mendel's researches made
upon the European mind up to Focke's time and later. In fact we
may say that his papers made no more or further impression, as
the evidence shows, than any other two contributions of equal
length, published during the time under consideration.

It is interesting to note the following extract from Focke's sec-
tion on "Xenias," (pp. 510-18). The paragraph discusses Goss's,
Seton's, and Knight's peas' experiments :

"J. Goss fertilized flowers of the blue-seeded pea, 'Prolific Blue," with
pollen of a white dwarf pea. The pods contained yellowish-white seeds
which, when sown, furnished plants whose pods contained in part blue,
in part white, in part seeds of both kinds. After selection, the blue sort
remained constant, the white produced in part pods with white, in part
pods with both kinds of seeds. (Trans. Hort. Soc. of London, V, p. 234.)
Knight, in his numerous crosses, never observed an immediate change of
the seed-color in consequence of the operation of foreign pollen. Alex.
Seton saw peas of two colors in the same pod, but just as in the case
of Goss arising in a hybrid (Blendling), not immediately in consequence
of foreign pollination. (Transact. Hort. Soc. London, V, pp. 236, 379.)
Recently, in the meantime, cases are also reported, in which such pods
with two kinds of seeds purport to be produced (erzeugt sein sollen)
directly in a blue-seeded sort through foreign pollen. (Deutsche Garten-
7,eit, 4 Jahrg, p. 71.) Gartner also obtained seeds a few times in his cross-
ing experiments, the color in which had deviated from the mother plant."
(1, p. 514.)

Knight's peas experiments having consisted in the crossing of

PLANT HYBRIDIZATION BEFORE MENDEL 215

a white-seeded by a grey-seeded variety, and the dominance of
seed-coat color not being evident until the following generation,
there would consequently be no xenia effect.

It is surprising, however, that Focke should have so clearly
overlooked the actual facts in the Goss experiment. The Blue
Prussian variety employed as the seed-parent had seeds with deep
"blue" cotyledons, or what would evidently properly be called
dark green. The pollen parent had "yellowish-white" seeds (i.e.,
cotyledons). As the result of the cross, Goss obtained three pods,
which contained, when ripe, instead of the "deep blue" seeds of
the maternal parent, yellowish-white seeds, like those of the pol-
len parent. There was thus a perfectly clear case of what is now
known as dominance, of the sort referred to by Focke as "xenia."
The case of Seton is somewhat similar. A grey-seeded pea (i.e.,
with grey seed-coats) was crossed with the pollen of a "white-
seeded" variety. A pod with four seeds was produced, all of which
are stated to have been green. There thus appears, so far as can
be judged, to have taken place in the first generation a dominance
of green cotyledon color over its absence (white), instead of the
usually reported case of the dominance of yellow cotyledon color
over green. That such was the case appears from the fact that the
seeds of the following year were mingled blue and white in the
pods, "mixed indiscriminately and in undefined numbers."

They were all completely either of one color, or of the other,
none of them having an intermediate tint. It is thus quite evident,
that dominance for "xenia") took place in the first generation,
followed by segregation in the second. Gartner's case should have
been noted of a cross of "Early Green Brockel" {Pisiun sativum
viride) with green cotyledons, with "White-flowered creeping pea"
(Pisum sativum nanum repens) with yellow seeds, in which a
pod with five seeds, all yellow, was produced as the result of the
cross. (Gartner, "Versuche und Beobachtungen," pp. 84-5.)

There was thus here a clear case of" color dominance ("xenia")
in the cotyledons Which does not appear to have particularly
attracted Focke's attention.

Focke was, until his death in October, 1922, a practising physi-
cian of the city of Bremen. His interest in all biological, and
especially in botanical questions, was considerable. He was like-
wise interested in philosophical problems, and was a vigorous

2i6 PLANT HYBRIDIZATION BEFORE MENDEL

supporter of Darwin. Focke was the founder of the Natural His-
tory Society in Bremen (1864), and until 1895 remained the editor
of its "Transactions." His best-known botanical contribution is
his "Pflanzenmischlinge" (1881), besides which he published in
1877 a "Synopsis Ruborum Germaniae" and "Species Ruborum,
Monographia, Generis Rubi Prodromus," published in the Biblio-
theka Botanica, 1914. He is reported as having contributed greatly
as a physician to the development of medical science in Bremen.
On his eightieth birthday, a "Festheft" appeared in his honor in
the Abhandlungen of the Natural History Society of Bremen,
Vol. 23.

28. The Hoffman Mendel Citations.

Aside from Focke's the only other reference to Mendel before
1900 is made by Hermann Hoffmann, "Untersuchungen zur Bes-
timmung des Werthes von Species and Varietat," at Giessen, 1869,
referred to by R. C. Punnett, in Nature, Vol. 116, p. 606, Octo-
ber 24, 1925.

Hoffman was Professor of Botany at Giessen, and became en-
gaged, from 1855, upon experiments with varieties of garden
beans, the results of which were reported in the Botanische Zei-
tung for 1862. As a result of these experiments it was found that
small variations which appeared in the seeds did not lead to the
formation of permanent new forms, but rather, on continued
(isolated) culture, reverted every tim^e immediately to the funda-
mental form. (p. 1.) The experiments were continued in the light
of Darwin's "Origin of Species" which appeared in 1859, the
object of the experiments being to determine whether new species
and varieties continue to originate from natural selection, or
through physical and similar influences. Hoffmann's contribution
of 1869 is therefore a study chiefly of variation, the question
being as to whether "varieties" can be "fixed."

The chief portion of the paper (pp. 47-80), is devoted to the
author's selection experiments with varieties of Phaseolus vul-
garis, x^lthough some crossing was attempted, the experiments are
almost entirely in selection for color in the seed-coat. The ultimate
aim of the investigation was the determination of the value of
species and varieties, and the fixability of varieties. Hoffmann
concludes (pp. 169-71) that certain varieties of Phaseolus vulgaris

PLANT HYBRIDIZATION BEFORE MENDEL 217

are "true species," and that the same is the case for some varieties
of peas, and that, in the case of Phaseolus multiflorus and several
so-called sub-species of P. vulgaris^ and in most of the white-

Plate XXXVIII. Hermann Hoffmann. Professor of Botany at the University of Giessen

(1855).

flowered varieties of blue or red-flowered species, and in a variety
of Pisum sativum^ color is not fixable.

Variation and the results of crossing are briefly discussed in the
case of 159 genera. Among these, under "Geum" (No. 71,

2i8 PLANT HYBRIDIZATION BEFORE MENDEL

p. 112), Mendel's reference to Gartner's cross of G. urhanum X
rivale is referred to as follows :

"From G. urhanum X rivale Gartner appears to have raised exceed-
ingly fertile and constant hybrids (according to Mendel, Verh. nat. hist.
Ver. Briinn. IV, p. 40). I do not find this verified on the reading of the
original. (Bast. Erz. 698)."

(The Mendel reference in question is found on p. 373 of Bate-
son's "Mendel's Principles of Heredity," under the caption "Con-
cluding Remarks," in Mendel's first paper.)

At p. 136 of Hoffmann, No. 118, under the heading of the
genus Pisum^ appears the following :

"Pisum in 6 years' observations by G. Mendel (Verh. Nat. Histor. Ver.
zu Briinn, 1865, IV, pp. 6 and 33). Hybrids of Pisum sativum, etc., from
forms true to seed."

After a considerable discussion of the possibilities in respect to
accidental crossing by insects (referring still to Mendel), Hoff-
mann concludes as follows:

"Hybrids possess an inclination in the following generation to strike
back to the parental species."

It seems extraordinary that, as Punnett remarks, although Hoff-
mann's somewhat extended experiments were carried on with
Phaseolus, he should have made no mention of Mendel's experi-
ments with this genus, which should have been easily noticed,
since they were reported upon toward the close of the paper on
peas. No mention is made of Mendel's paper on Hieracium crosses,
although a brief paragraph (No. 75, p. 144) is devoted by Hoff-
mann to Hieracium variation studies.

BIBLIOGRAPHY

Focke, Wilhelm Olbers.

Die Pflanzenmischlinge, ein Beitrag zur Biologic der Ge-

wachse. Berlin, 1881.

Gartner, Carl Friedrich von.

(a) Versuche und Beobachtungen iiber die Befruchtungsor-
gane der vollkommeneren Gewachse, und iiber die na-

PLANT HYBRIDIZATION BEFORE MENDEL 219

tiirliche und kiinstliche Befruchtung durch den eigenen
Pollen. Naturwissenschaftliche Abhandlungen, Tiibin-
gen 1:1.

(b) Notice sur des experiences concernant la fecondation
de quelques vegetaux. Annales des sciences naturelles,
10: 113-48, 1827. (Translation of the preceding.)

(c) Beantwoording der Prysvraag over Bastardeering. Na-
tuurkundige Verhandelingen van de HoUandische Maat-
schappy van Wetenschappen te Haarlem. 1844.

(d) Over de Voortteling van Baastard-Planten. Eene Biitrage
tot de Kennis van de Bevruchting der Gewassen. Haar-
lem, 1838.

(e) Beitrage zur Kenntniss der Befruchtung. Stuttgart,
1849.

(f) Versuche und Beobachtungen iiber die Bastarderzeugung
im Pflanzenreich. Stuttgart, 1849.

(g) Methode der kiinstlichen Bastardbefruchtung der Ge-
wachse, und Namensverzeichniss der Pflanzen mit wel-
chen Versuche eingestellt wurden. Stuttgart, 1849.

3. Hojjmayin^ Hermann.

Untersuchungen sur Bestimmung des Werthes von Species
und Varietat : ein Beitrag zur Kritik der Darwin'schen
Hypothese. Giessen, 1869, pp. 171.

4. Ndgeli^ Carl von.

(a) tJber den Einfluss der ausseren Verhaltnisse auf die
Varietatenbildung im Pflanzenreiche. Botanische Mit-
theilungen, 2: 103-58. November 18, 1865.

(b) tJber die Bedingungen des Vorkommens von Arten und
Varietaten innerhalb ihres Verbreitungsbezirkes. Sit-
zungsberichte der koniglichen Akademie der Wissen-
schaften zu MiJnchen, 2:23a. December 15, 1865. Bot-
anische Mittheilungen, 2: 159-87.

235-

(d) tJber die abgele'<"eten Pflanzenbastarde. ibid., January
13, 1866. Botanische Mittheilungen, 2 : 237-59.

220 PLANT HYBRIDIZATION BEFORE MENDEL

(e) Die Theorie der Bastardbildung. ibid., January 13, i856.
Botanische Mittheilungen, 2 : 259-93.

(f) Die Zwischenformen zwischen den Pflanzenarten. ibi^.,
February 16, 1866. Botanische Mittheilungen, 2:294-

339-

(g) Intermediate forms in plants. Gardeners' Chronicle,

p. 405, 1867.
(h) Die systematische Behandlung der Hieracien, riicksicht

lich der Mittelformen. ibid., March 10, 1866. Botanische

Mittheilungen, 2 : 340-69.
(i) Mechanisch-physiologische Theorie der Abstammungs-

lehre. Munich, 1884.

5. Kegel, Eduard August.

tJber Varietaten und Bastarde im Pflanzenreiche. Mittheilun-
gen der naturforschenden Gesellschaft im Ziirich. (1). Heft
2 : 69-71. January, 1848.

6. Wichura, Max.

Die Bastardbefruchtung im Pflanzenreich, erliiutert an den
Bastarden der Weiden. Breslau, 1865.

7. Wiegmann, A. F.

tJber die Bastarderzeugung im Pflanzenreiche. Braunschweig,
1828.

CHAPTER VII

THE WORK OF CHARLES DARWIN

29. Darwin s Contribution to the Theory of Hybrids.

THE period from 1859 until the rediscovery of Mendel's
papers in 1900 was so strongly colored by the views of
Charles Darwin, and so dominated by the magnitude of
his work, that it sometimes seems as though originality and initia-
tive during that period had been considerably abandoned, and as
though, so far as evolution was concerned, the scientific world
had remained content simply to quote the work of Darwin.

It is the purpose of the present chapter to present the contribu-
tions of Darwin to the knowledge of hybrids. To this end it seems
desirable, so far as possible, to let Darwin's words speak for
themselves, and hence, although the text may seem burdened with
extracts, yet, for those interested in tracing the history of ideas in
genetics, it will perhaps be of service to assemble such a resume
of Darwin's work and thought in the field of hybridization.
Brought together in such a way, an author's contribution can be
more successfully evaluated at leisure by those who may be in-
terested. The writer has therefore sought to bring together, in
somewhat connected and coherent form, the various views, con-
clusions, and experimental data on the subject of hybrids and
hybridization found in Darwin's different writings.

On November 24, 18^9, appeared the first edition of "The
Origin of Species" (la), antedating by seven years the appear-
ance of the papers of Mendel.

One of the primary questions concerning crossing that inter-
ested Darwin was the matter of sterility and fertility in hybrids.
Investigators before Darwin's time had been to a considerable
extent obsessed by the species question, which crossing was sup-
posed to solve. If a cross succeeded, or produced fertile offspring.

222

PLANT HYBRIDIZATION BEFORE MENDEL

it argued that the parent forms were "varieties." If the cross
failed, or if its offspring were sterile, it demonstrated that they
were "species." With the sole exception of Sageret (2), none of
the earlier hybridists seems to have formed, as the result of ex-
periment, anything like the modern conception of characters as

PUTE XXXIX. Charles Darwin, 1809-1882.

PLANT HYBRIDIZATION BEFORE MENDEL 223

biological units, and, with the sole exception of Naudin and
Darwin, no scientihc theory was even conceived of, which might
explain the modus operandi of amphimixis in the case of hybrids.
By Darwin the question of hybridization, while indeed for the
most part taken up more or less conventionally, received neverthe-
less broader treatment. To begin with, Darwin held that the in-
ability of species to cross

". . . is often completely independent of their systematic affinity, that is
of any difference in their structure or constitution, excepting in their
reproductive systems." (la, 2:14.)

So that, even as early as the writing of the "Origin of Species,"
Darwin is seen to maintain that the susceptibility of plants to
crossing stood in no necessary relation to the degree of their re-
semblance, and that

". . . facility of making a first cross between any two species is not
always governed by their systematic affinity or degree of resemblance
to each other." (la, 2:16.)

This fact, he adds, is demonstrated by the case of reciprocal
crosses, alluding here to the relative facility of making the cross,
according as the one or the other species is used as the male or
the female.

"Occasionally," he says, there is "the widest possible difference, in the
facility of effecting a union. The hybrids, moreover, produced from
reciprocal crosses, often differ in fertility." {ib.)

Darwin again later, in "Animals and Plants under Domestica-
tion," refers to the matter as follows :

"why should some species cross with facility, and yet produce very
sterile hybrids ; and other species cross with extreme difficulty, and yet
produce fairly fertile hybrids'? Why should there often be so great a
difference in the result of a reciprocal cross between the same two
species*?" {ib., p. 217.)

Darwin comments frequently, in the "Origin of Species," upon
the fact that the hybrids produced from reciprocal crosses often
differ in fertility, and that, while two species may be difficult to
cross, there is no strict parallelism between the difficulty of effect-
ing the cross, and the degree of sterility of the hybrids resulting
therefrom.

As Darwin observes, difference in the results, in respect to the
relative ease of making reciprocal crosses, had been previously
noted by Kolreuter, who found, after two hundred trials con-

224 PLANT HYBRIDIZATION BEFORE MENDEL

tinued over a period of eight years, that, while Mirabilis jalapa
could easily be fertilized by M. longiflora, the reverse cross could
not be effected. With regard to the difference in the facility with
which reciprocal crosses can be made, there may be some funda-
mental resemblance between this fact and the ease with which
reciprocal grafts can be made, wherein Darwin instances the fact
that the currant can, although with difificulty, be grafted upon
the gooseberry, while the reciprocal graft cannot be made. Cer-
tainly the well-established truth of factorial mutations in vegeta-
tive cells, followed by germinal differences to correspond, should
sufficiently indicate that the behavior of the somatic and of the
reproductive cells ought not to be regarded as being so sharply
separated as is usually done. At all events, the problem of the
reason for the relative difference in the respective facility of mak-
ing reciprocal crosses, as well as the further one of such differ-
ences as exist, in the case of mule and hinny, between the re-
spective products of reciprocal crosses, are questions that have
been too little investigated since Darwin's time, and require ex-
planation.

Since the advent of Mendelian studies in 1900, it has been
rather conventionally assumed that reciprocal crosses are more
or less identical in type. That such is not necessarily the case,
Darwin's early observations should suffice to indicate.

The problem of the fertility of selfed and crossed plants en-
gaged Darwin's close interest. In forty-one cases, belonging to
twenty-three species, the ratio of the fertility of the crossed to
that of the self-fertilized plants, was found to be as 100:60.
In another experiment to determine the relative fertility of flow-
ers when crossed or selfed, the ratio in thirty cases, belonging to
twenty-seven species, was as 100:55".

There is no evidence, Darwin finds,

". . . that the fertility of plants goes on diminishing in successive self-
fertilized generations," and "no close correspondence, either in the parent
plants or in the successive generations, between the relative number of
seeds produced by the crossed and self-fertilized flowers, and the relative
powers of growth of the seedlings raised from such seeds." (lb, p. 327.)

Darwin's investigations were directed quite extensively to the
question of self-sterility in plants, a field which bears strongly

PLANT HYBRIDIZATION BEFORE MENDEL 225

upon our knowledge of heredity, but in which likewise, until re-
cently, comparatively little experimental work had been done
since his time. As the result of his own studies, supplemented by
those of Hildebrand and Fritz Miiller, he was able to say:

"We may therefore confidently assert, that a self-sterile plant can be
fertilized by the pollen of any one of a thousand or ten thousand in-
dividuals of the same species, but not by its own." {ib., p. 347.)

Regarding all the causes of sterility, or inability to accept
fertilization, we are still somewhat at a loss for a complete ex-
planation, although recent chromosome discoveries are throwing
light upon the subject. Darwin states the situation in his time:

"The veil of secrecy is as yet far from lifted ; nor will it be until we
can say why it is beneficial that the sexual elements should be differ-
entiated to a certain extent, and why, if the differentiation be carried
still further, injury follows. It is an extraordinary fact, that, with many
species, flowers fertilized with their own pollen are either absolutely or
in some degree sterile ; if fertilized with pollen from another flower on
the same plant, they are sometimes, though rarely, a little more fertile ;
if fertilized with pollen from another individual or variety of the same
species, they are fully fertile ; but if with pollen from a distant species
they are sterile in all possible degrees, until utter sterility is reached.
Thus we have a long series with absolute sterility at the two ends ; at
one end due to the sexual elements not having been differentiated, and
at the other end to their having been differentiated in too great a degree,
or in some peculiar manner." {ib., pp. 460-1.)

The questions which Darwin raises in this connection are as fol-
lows (p. 458) :

1. Why the individuals of some species profit greatly, others
very little, by being crossed. .

2. Why the advantages from crossing seem to accrue exclu-
sively now to the vegetative and now to the reproductive
system, although generally to both.

3. Why some members of a species should be sterile, while
others are entirely fertile with their own pollen.

4. Why a change of environment or of climate should affect
the sterility of self-sterile specPes.

5- Why the members of some species should be more fertile
with the pollen from another species than with their own.

Regarding the general matter of sterility in hybrids, Darwin
comments as follows :

"it is notorious that, when distinct species of plants are crossed, they
produce, with the rarest exceptions, fewer seeds than the normal num-

226 PLANT HYBRIDIZATION BEFORE MENDEL

ber. This unproductiveness varies in different species up to sterility so
complete that not even an empty capsule is formed." (lb, p. 468.)

"it is also notorious that not only the parent species, but the hybrids
raised from them, are more or less sterile, and that their pollen is often
in a more or less aborted condition. The degree of sterility of various
hybrids does not always strictly correspond with the degree of difficulty
in uniting the parent forms. When hybrids are capable of breeding
inter se, their descendants are more or less sterile, and they often be-
come still more sterile in the later generations." {ib., p. 469.)

"with the majority of species, flowers fertilized with their own pollen
yield fewer, sometimes much fewer seeds, than those fertilized with
pollen from another individual or variety." (ib., p. 469.)

As the result of his investigations regarding sterility of pollen,
Darwin was able to render at least one service, that of removing
the obsession which had so long afflicted the study of the hybrid
question, viz., the variety-species discussion. He says:

"it can thus be shown that neither sterility nor fertility affords any
certain distinction between species and varieties. The evidence from this
source graduates away, and is doubtful in the same degree as is the
evidence derived from other constitutional and structural differences."
(la, 2:4.)

The question of the chemical and cytological basis for sterility
or non-receptivity to pollen remains still in part a field for the
investigator.

One of the most important questions from the present-day
viewpoint which Darwin investigated was that of heterosis, the
relative vigor of the first generation hybrids as compared with
that of their parents. The following allusions occur in the "Origin
of Species."

Darwin comments on the fact that crosses between individuals
of the same species, where they differ to a certain extent, give
increased vigor and fertility, while close-fertilization long con-
tinued almost always leads to physical degeneracy, and re-
marks :

"We know also that a cross between distinct individuals of the same
variety, and between distinct varieties, increases the number of the off-
spring, and certainly gives to them increased size and vigour." (la,
2 : 269.)

Darwin thoroughly investigated, as is well known, the com-
parative relation of the offspring of crossed to those of selfed
plants with respect to vigor.

"I have made so many experiments, and collected so many facts, show-
ing on the one hand that an occasional cross with a distinct individual

PLANT HYBRIDIZATION BEFORE MENDEL 227

or variety increases the vigour and fertility of the offspring, and on
the other hand that very close interbreeding lessens their vigour and
fertility, that I cannot doubt the correctness of this conclusion." (2a,

"Again, both with plants and animals, there is the clearest evidence
that a cross between individuals of the same species, which differ to a
certain extent, gives vigour and fertility to the offspring; and that close
interbreeding continued during several generations between the nearest
relations, if these be kept under the same conditions of life, almost al-
ways leads to decreased size, weakness, or sterility." (la, 2:27-8.)

In "Cross and Self-Fertilization," Darwin again discusses the
effects of crossing as follows, expressing the view :

"Firstly, that the advantages of cross-fertilization do not follow from
some mysterious virtue in the mere union of two distinct individuals,
but from such individuals having been subjected during previous genera-
tions to different conditions, or to their having varied in a manner com-
monly called spontaneous, so that in either case their sexual elements
have been in some degree differentiated; and secondly, that the injury
from self-fertilization follows from the want of such differentiation in
the sexual elements." (lb, p. 448.)

"After plants have been propagated by self-fertilization for several
generations, a single cross with a fresh stock restores their pristine
vigour and we have a strictly analogous result with our domestic ani-
mals." (lb, p. 444.)

"A cross with a fresh stock, or with another variety, seems to be always
beneficial whether or not the mother plants have been intercrossed or
self-fertilized for several previous generations." (lb, p. 449.)

Darwin also remarks upon the greater power of the cross-
fertilized plants in his experiments to stand exposure, the crossed
plants enduring sudden removal from greenhouse to out-of-doors
conditions better than did the self-fertilized, and also resisting
cold, and intemperate weather conditions more successfully. This
was the case with morning-glory and. with Mimulus.

"The offspring of plants of the eighth self-fertilized generation of
Mimulus, crossed by a fresh stock, survived a frost which killed every
single self-fertilized and intercrossed plant of the old stock." (lb,
p. 289.)

"Independently of any external cause which could be detected, the
self-fertilized plants were more liabre to premature death than the
crossed." {ib., p. 290.)

Out of several hundred plants in all, involved in the experi-
ment, only seven of the crossed plants died, while at least twenty-
nine of the self-fertilized were thus lost.

With regard to time of flowering, in four out of fifty-eight
cases a crossed, in nine cases a selfed, plant flowered first.

228 PLANT HYBRIDIZATION BEFORE MENDEL

Darwin broached the view that the increased vigor of first
generation hybrids was chiefly due to the forms used in the cross
having been exposed to somewhat different conditions of life. He
also contended that his experiments proved that:

"if all the individuals of the same variety can be subjected during
several generations to the same conditions, the good derived from cross-
ing is often much diminished or wholly disappears." (la, 2:270.)

This statement appears to be an obiter dictum of Darwin's, to
the support of which he does not adduce direct experimental evi-
dence.

Again he says :

"Anyhow my experiments indicate that crossing plants, which have
been long subjected to almost though not quite the same conditions,
is the most powerful of all the means for retaining some degree of
differentiation in the sexual elements, as shown by the superiority in the
later generations of the intercrossed over the self-fertilized seedlings."

(lb, pp. 454-5-)

"We know," he says, "that a plant propagated for some generations in
another garden in the same district serves as a first stock, and has high
fertilizing powers." {ib., p. 455.)

The importance of this view has yet, so far as the writer
knows, to be re-investigated under controlled conditions.

It was Darwin's view, as the result of his experiments, that
the increased vigor of intercrossed plants is due to the constitu-
tion or nature of the sexual elements, which conditions he took
to be of the general nature of differentiation due to the action of
environment.

"It is certain," he says, "that the differences are not of an external
nature, for two plants which resemble each other as closely as the in-
dividuals of the same species ever do, profit in the plainest manner when
intercrossed, if their progenitors have been exposed during several gen-
erations to different conditions." (lb, p. 270.)

Darwin asserts that there is not a single case in his experi-
ments

". . . which affords decisive evidence against the rule that a cross be-
tween plants, the progenitors of which have been subjected to some-
what diversified conditions, is beneficial to the offspring." {ib., p. 281.)

The fact that increased vegetative vigor In first generation hy-
brids was also sometimes accompanied by diminished fertility
was likewise observed by Darwin.

"For it deserves especial attention that mongrel animals and plants.

PLANT HYBRIDIZATION BEFORE MENDEL 229

which are so far from being sterile that their fertility is often actually
augmented, have, as previously shown, their size, hardiness, and constitu-
tional vigour generally increased. It is not a little remarkable that an
accession of vigour and size should thus arise under the opposite contin-
gencies of increased and diminished fertility," (ic, 2: 108.)

In the case of Darwin's experiments to determine the relative
effects upon vigor of selling and crossing, respectively, the data
were determined chiefly with respect to height and weight of the
plants, which were grown on opposite sides of the same pot in
all instances.

Regarding the relative heights and weights of 292 plants de-
rived from a cross with a fresh stock, and of 305 plants either
selfed or intercrossed between plants of the same stock, and be-
longing to thirteen species and twelve genera, Darwin says :

"Considering all the cases . . . there can be no doubt that plants profit
immensely, though in different ways, by a cross with a fresh stock, or
with a distinct sub-variety." He emphasizes further, "it cannot be main-
tained that the benefit thus derived is due merely to the plants of the
fresh stock being perfectly healthy, whilst those which had been long
intercrossed or self-fertilized had become unhealthy; for in most cases
there was no appearance of such unhealthiness." {ib., p. 269.)

Experiments were also made with plants belonging to five
genera in four different families. One of the most interesting
cases was that of a plant of marjoram (^Origanum vulgar e). The
height of the crossed was to that of the selfed as 100 : 86.

"They differed also to a wonderful degree in constitutional vigour.
The crossed plants flowered first, and produced twice as many flower-
stems; and they afterwards increased by stolons to such an extent as
almost to overwhelm the self-fertilized plants." (lb, p. 302.)

Darwin holds that the inferiority of the selfed seedlings in
height can have been in no way due to any morbidity or disease
in the mother plants ; certainly, he maintains, no such theory of
a diseased condition would in anywise hold, in the case of

". . . intercrossing the individuals of the same variety or distinct va-
rieties, if these have been subjected durilig some generations to different
conditions." (lb, p. 450.)

In four out of the five cases experimented with, the intercrossing
of flowers upon the same plant did not differ in effect from the
strictest self-fertilization. He says :

"On the whole, the results here arrived at . . . agree well with our
general conclusion that the advantage of a cross depends on the progeni-
tors of the crossed plants possessing somewhat different constitutions,

23C PLANT HYBRIDIZATION BEFORE MENDEL

either from having been exposed to different conditions, or to their hav-
ing varied from unknown causes in a manner which we in our ignor-
ance are forced to speak of as spontaneous." (lb, pp. 302-3.)

Darwin's experiments indicated, as in the case of heartsease
and sweet peas, that

". . . the advantage derived from a cross between two plants was not
confined to the offspring of the first generation." (lb, p. 305.)

"Laxton's varieties [of sweet peas] produced by artificial crosses," as
Darwin says, "have retained their astonishing vigour and luxuriance for
a considerable number of generations." {ib., p. 305.)

Darwin concludes :

"As the advantage from a cross depends on the plants which are
crossed differing somewhat in constitution, it may be inferred as prob-
able that under similar conditions a cross between the nearest relations
would not benefit the offspring so much as one between non-related
plants." {ib., p. 305.)

Darwin finally also remarks in general :

"it is interesting to observe . . . the graduated series from plants
which, when fertilized by their own pollen, yield the full number of seeds,
but with the seedlings a little dwarfed in stature, to plants which, when
self-fertilized, yield few seeds, to those which yield none, but have their
ovaria somewhat developed, and, lastly, to those in which the plant's
own pollen and stigma mutually act on one another like poison." (ic,
2: 119.)

The relative weight and germinative energy of seeds from
crossed and from self-fertilized plants, was investigated by Dar-
win in the case of sixteen species, with the result that the weight
of the seeds of the former to that of the latter was found on
the average to be as 100:96. In ten out of the sixteen cases, the
self-fertilized seeds were either equal or superior to the crossed
in weight, and in six out of these ten, the plants raised from these
selfed seeds were greatly superior in height and in other respects
to those from the crossed seeds. In the matter of the germination
of selfed and crossed seeds, the results were conflicting. Darwin,
however, discovered that, in general, seedlings of greater con-
stitutional vigor are obtained when crossed by other individuals
of the same stock than when pollinated by their own pollen.

In plants of fifty-seven different species belonging in all to
fifty-two genera and to thirty different families, Darwin carried
out the most extensive experiment yet on record, conducted for
the purpose of determining the difference in size between the off-
spring of cross-fertilized and of close-fertilized plants.

PLANT HYBRIDIZATION BEFORE MENDEL 231

The total number of the crossed plants amounted to 1,101, and
of the selfed plants to 1,076. As a result, Darwin found that the
plants derived from crosses between different strains of the same
species were taller on the average, than plants derived from
crosses within the same strain, and taller in the latter case than
in the case of the offspring of self-fertilized plants. The average
ratio of 620 crossed to 607 selfed plants in respect to height, de-
rived from Darwin's tables, was as 100:86.

From the fact that flower buds are in a sense distinct individual
plant units, which sometimes vary and differ widely from one
another, and yet, when on the same plant, owing to the fact that
the whole plant has come from the same fertilized cell, rarely are
widely differentiated, Darwin reasons that the effects of inter-
crossing can be explained. He says :

"The fact that a cross between two flowers on the same plant does no
good or very little good, is likewise a strong corroboration of our con-
clusion ; for the sexual elements in the flowers on the same plant can
rarely have been differentiated, though this is possible, as flower buds
are in one sense distinct individuals, sometimes varying and differing
from one another in structure and constitution." (lb, p. 449.)

"Thus," he concludes, "the proposition that the benefit from cross
fertilization depends on the plants which are crossed having been sub-
jected during previous generations to somewhat different conditions, or to
their having varied from some unknown cause as if they had been thus
subjected, is securely fortified from all sides." (lb, p. 449.)

Darwin comments also on the reversed situation, where changes
in the external conditions result in sterility, for which he seeks to
find a logical connection with the condition induced by crossing.

"For as, on the one hand, slight changes in the conditions of life are
favourable to plants and animals, and the crossing of varieties adds to
the size, vigour, and fertility of their offspring, so, on the other hand,
certain other changes in the conditions of life cause sterility ; and as
this likewise ensues from crossing much modified forms or species, we
have a parallel and a double series of facts which apparently stand in
close relation to each other." (ic, 2:126.)-

Darwin appears to hold the ill effects of close fertilization to
be due to the fact that the sexual elements in the different flow-
ers on the same plant have not differentiated, while in his con-
clusion he appears to consider the benefits of cross-fertilization
to be due to the individuals involved in the cross having been
differentiated through being exposed to different conditions.

232 PLANT HYBRIDIZATION BEFORE MENDEL

Darwin frequently emphasizes the same view regarding the
differentiating effects of a new environment.

"But hardly any cases afford more striking evidence how powerfully
a change in the conditions of life acts on the sexual elements, than those
already given, of plants which are completely self-sterile in one country,
and when brought to another, yield, even in the first generation, a fair
supply of self-fertilized seeds." (lb, p. 452,) And again, ". . . We know
that a plant propagated for some generations in another garden in the
same district serves as a fresh stock and has high fertilizing powers.
The curious cases of plants which can fertilize and be fertilized by any
other individual of the same species, but are altogether sterile with
their own pollen, become intelligible, if the view here propounded is
correct, namely, that the individuals of the same species growing in a
state of nature near together have not really been subjected during sev-
eral previous generations to quite the same conditions." (lb, pp. 455-6.)

"when two varieties which present well-marked differences are crossed,
their descendants in the later generations differ greatly from one another
in external characters; and this is due to the augmentation or oblitera-
tion of some of these characters, and to the reappearance of former ones
through reversion ; and so it will be, as we may feel almost sure, with
any slight differences in the constitution of their sexual elements." (lb,
p. 454.)

With regard to the ill effects derived from self-fertilization,
Darwin says :

"whether with plants the evil from self-fertilization goes on increas-
ing during successive generations is not as yet known ; but we may infer
from my experiments that the increase, if any, is far from rapid. After
plants have been propagated by self-fertilization for several genera-
tions, a single cross with a fresh stock restores their pristine vigour,
and we have a strictly analogous result with the domestic animals. The
good effects of cross-fertilization are transmitted by plants to the next
generation; and, judging from the varieties of the common pea, to many
succeeding generations. But this may merely be that crossed plants of
the first generation are extremely vigorous, and transmit their vigour,
like any other character, to their successors." (lb, p. 444.)

In this paragraph, Darwin calls attention to a fact already
referred to, that attracted little attention for a generation, viz.,
the immediate improvement due to a cross, known as "heterosis."
Darwin was thus, if not the first to call sharply to attention the
matter of the relatively increased size and vigor of first genera-
tion hybrids, at least the first to subject the question to experi-
mental analysis.

Darwin supposed that what occurred in the case of hybridiza-
tion was a general breaking-up of the plant's characters, hybrid-
ization being understood to operate in about the same wav upon
the plant's organization as do changes in the external conditions.

PLANT HYBRIDIZATION BEFORE MENDEL 233

"Thus," Darwin says, "when organic beings are placed during several
generations under conditions not natural to them, they are extremely
liable to vary, which seems to be partly due to their reproductive systems
having been specially affected, though in a lesser degree than when ste-
rility ensues. So it is with hybrids, for their offspring in successive
generations are eminently liable to vary, as every experimentalist
knows." (la, 2: 26.)

And further :

"Now hybrids in the first generation are descended from species (ex-
cluding those long cultivated) which have not had their reproductive
systems seriously affected, and their descendants are highly variable."
(la, 2:41.)

Darwin deserves credit for stoutly contesting the point of view
then widely current that the longer a character is handed down
by a breed, the more force per se it will carry in the transmission.
Discussing some of the cases, he says :

"in none of these, nor in the following cases, does there appear to be
any relation between the force with which a character is transmitted and
the length of time during which it has been transmitted." (ic, 2:37.)

The basis for such a view, that the longer a strain is grown,
and the more it is selected, the more uniform, i.e., the more ho-
mozygous, it becomes, was not scientifically known in Darwin's
time, but Darwin acutely perceived that the mere repeated act of
selection itself, whatever else might be involved, would not nec-
essarily increase the "potency" of transmission.

Darwin's view as to the reason for the good effects of crossing
was based upon the long prevalent opinion that, since animals,
and hence presumably plants, profit from changes in their condi-
tions, probably such changes operate to affect the germ cells, or
that in some way the germ cells receive an extra stimulation on
that account which redounds to the benefit of the offspring,
(ic, 2:155.)

So far as variability is concerned, Darwin holds :

"That variability of every kind is directly or indirectly caused by
changed conditions of life. Or, to put the case from another point of
view, if it were possible to expose all the individuals of a species during
many generations to absolutely uniform conditions of life, there would
be no variability." (ic, 2:234.)

Darwin quotes Pallas to the effect that all variation is due to
crossing, to which view, however, he opposed the facts of bud-
variation. It remained Darwin's view, as it was that of practically

234 PLANT HYBRIDIZATION BEFORE MENDEL

all of the older school of breeders, that it was probable that
crossing in and of itself, when one or both the parents have been
long under cultivation, increases the "variability" of the offspring,
independently of the fact of the commingling of the parental
characters themselves, (ic, 2:243-4.)

The fundamental cause underlying variation Darwin con-
sidered to be the food supply.

"of all the causes which induce variability," he says, "excess of food
whether or not changed in nature, is probably the most powerful."
(ic, 2:236.)

However, in face of the fact of the bud variation of the peach
to form the nectarine, Darwin concluded that there must have
been some cause, internal or external, to stimulate a bud to
change its character. He says :

"l cannot imagine a class of facts better adapted to force on our minds
the conviction that what we call the external conditions of life are in
many cases quite insignificant in relation to the particular variation, in
comparison with the organization or constitution of the being which
varies." (ic, 2 : 269.)

So, from the case of the red Magnum Bonu7n plum, which ap-
peared on a forty-year old tree of the yellow Magnum Bonum
variety, Darwin also concludes :

"when we reflect on these facts, we become deeply impressed with
the conviction that in such cases the nature of the variation depends but
little on the conditions to which the plant has been exposed, and not
in any special manner on its individual character, but much more on
the inherited nature or constitution of the whole group of allied beings
to which the plant in question belongs. We are thus driven to conclude
that in most cases the conditions of life play a subordinate part in
causing any particular modification ; like that which a spark plays, when
a mass of combustibles bursts into flame, the nature of the flame de-
pending on the combustible matter, and not on the spark." (ic, 2:272.)

In general, regarding the character of hybrids, Darwin held
that while in the majority of cases, the hybrid offspring are inter-
mediate between their parents, yet that certain characters are in-
capable of fusion.

"when two breeds are crossed, their characters usually become inti-
mately fused together; but some characters refuse to blend, and are
transmitted in an unmodified state, either from both parents or from
one." (ic, 2 : 67.)

As cases in point, Darwin cites the crossing of gray and white
mice, the offspring of which are pure white or gray, but not inter-

PLANT HYBRIDIZATION BEFORE MENDEL 235

mediate, and the crossing of white, black, and fawn-colored an-
gora rabbits, in which the colors are separately inherited, and not
combined in the same animal. The non-intermediate character of
the inheritance in the case of turnspit dogs and ancon sheep is
referred to, as is also the inheritance in the case of tailless, horn-
less breeds. Similar results in the case of stocks, toad-flax, and
sweet peas are cited, (ic, 2:68.)

Darwin (ic, 2:44-45; 68-69), ^^ discussing what he called
"prepotency," is dealing in very many cases with that which we
now recognize as simple dominance. For example, in the crossing
of snap-dragons Darwin found that when the normal or irregular-
flowered (zygomorphic) type is crossed reciprocally with the pe-
loric or regular-flowered (actinomorphic) type, the former prevails
in the first generation to the exclusion of the latter. The 127 hy-
brid plants, self-fertilized, yielded in the second generation irreg-
ular to regular plants in the ratio of 88 to 37. This is evidently
an approximation to the 3:1 ratio, its defectiveness being un-
doubtedly due to the limited numbers.

Darwin, however, regards it simply as a

". . . good instance of the wide difference between the inheritance of a
character and the power of transmitting it to crossed offspring." (ic.
2:45.)

Darwin was thus quite unable, with the information then
available, to frame a satisfactory explanation for the various
phenomena passing under the name of "prepotency."

He makes one remark relative to prepotency, however, which
slightly grazes the recent presence-and-absence theory of Men-
delian inheritance.

"We can seldom tell what makes one race or species prepotent over
another; but it sometimes depends on the same character being present
and visible in one parent, and latent or potentially present in the other."
(ic, 2:58.)

The fact that certain characters are bound up with sex, or
"sex-linked," did not escape Darwin's observation. He alludes to
cases where a son does not inherit a character directly from his
father, or transmit it directly to his son, but receives it by trans-
mission from a mother who does not show it herself, and where
he transmits it in turn through the medium of a daughter, who
also does not show the character, but who acts as a carrier.

236 PLANT HYBRIDIZATION BEFORE MENDEL

"characters may first appear in either sex, but oftener in the male
than in the female, and afterwards be transmitted to the offspring of
the same sex. In this case, we may feel confident that the peculiarity in
question is really present, though latent, in the opposite sex. Hence the
father may transmit through his daughter any character to his grand-
son; and the mother conversely to her granddaughter. We thus learn,
and the fact is an important one, that transmission and development
are distinct powers. Occasionally these two powers seem to be antagon-
istic, or incapable of combination in the same individual; for several
cases have been recorded in which the son has not directly inherited a
character from his father, or directly transmitted it to his son, but has
received it by transmission through his non-affected mother, and trans-
mitted it though his non-affected daughter. Owing to inheritance being
limited by sex, we see how secondary sexual characters may have arisen
under nature ; their preservation and accumulation being dependent on
their service to either sex." (ic, 2:58-9.)

Darwin's mind was chiefly occupied, not with the question of
the fundamental nature of hybridity, but, as we have seen, with
the question of the relative sterility of selfed and crossed plants,
and their relative vigor. However, among the interesting matters
from the genetic standpoint, are his recognition of the general
fact of the intermediacy of first-generation hybrids, and the oc-
casional dominance of one or the other set of parental characters,
and the phenomenon called "reversion."

It is in connection with the question of reversion that we find
the greatest theoretical interest in Darwin's writings on the sub-
ject of hybridization. On this subject of "reversion," Darwin's
utterances are remarkable, especially in "Animals and Plants
under Domestication." In most cases he regards "reversion" as
the coming to light of a "latent" character, as e.g. :

". . . hornless breeds of cattle possess a latent capacity to produce horns,
yet when crossed with horned breeds, they do not invariably produce
offspring bearing horns." (ic, 2:44.)

Darwin considered it doubtful whether, as was then popularly
supposed, the length of time during which a character had been
inherited had any influence on its fixedness, and concludes, from
the fact that, when wild species which had remained so for ages
are brought into cultivation, they immediately begin to vary,
that no character can be considered as absolutely fixed by long
inheritance, (ic, 2:56.)

As previously stated, one of the problems that primarily in-
terested Darwin was the question of sterility and fertility in hy-
brids, the fact of sterility being relied upon to prove that the

PLANT HYBRIDIZATION BEFORE MENDEL 237

parents belonged to different "species," whereas fertility indicated
that the parents were varieties of the same species. At present,
while it is recognized that organisms more distantly related — ■
frequently different so-called "species" — do not ordinarily cross,
or, if they do, the progeny are quite frequently sexually sterile,
yet the attitude has quite changed from the strictly systematic
point of view formerly adhered to. Darwin recognized in general
that :

"There is often the widest possible difference in the facility of mak-
ing reciprocal crosses. Such cases are highly important, for they prove
that the capacity in any two species to cross is often completely inde-
pendent of their systematic affinity, that is of any difference in their
structure or constitution, excepting in their reproductive systems." (la,
2: 14.)

Darwin's relation to the study of hybridization is, as already
stated, chiefly known through his extensive and classical experi-
ments on self and cross-fertilization in plants.

In forty cases, belonging to twenty-three species, the ratio of
the fertility of the crossed to that of the self-fertilized plants was
found to be as 100:50 {ib., pp. 314-17); in another case, the
ratio, in thirty cases, belonging to twenty-eight species, was as

100:75. (2'^-' PP- 322-3.)

Darwin, at the outset, merely comments on the results of cross-
ing as follows :

"In considering the final result of the commingling of two or more
breeds, we must not forget that the act of crossing in itself tends to
bring back long-lost characters not proper to the immediate parent-
forms." (ic, 2*: 64.)

It was noticed that from three to eight generations were usually
required before a breed derived from a cross comes to be con-
sidered free from danger of "reversion." What constituted the
machinery to bring about reversion remained, but for Mendel's
as yet undiscovered researches, unknown. The state of knowledge
in this regard is exemplified by Darwin's remark :

"That the act of crossing in itself gives an impulse towards reversion,
as shown by the re-appearance of long-lost characters, has never, I be-
lieve, been hitherto proved." (ic, 2:13.)

Darwin recognized, as did most of the breeders before Mendel,

that:

"As a general rule, crossed offspring in the first generation are nearly

238 PLANT HYBRIDIZATION BEFORE MENDEL

intermediate between their parents, but the grandchildren and succeed*
ing generations continually revert, in a greater or lesser degree, to one
or both of their progenitors." (ic, 2:22.)

From cases of intermediacy, Darwin proceeds to discuss what
we should call cases of dominance, and finally cases in which the
offspring in the first generation are neither intermediate nor uni-
parental in ' type, but in which there is vegetative splitting, or
mutation :

"in which differently coloured flowers borne on the same root resemble
both parents, , . . and those in which the same flower or fruit is striped
or blotched with the two parental colours, or bears a single stripe of
the colour or other characteristic quality of one of the parent-forms."
(ic, 2:69.)

It is interesting to see how Darwin now undertook, in the ab-
sence of experimental evidence, to devise a scientific solution for
the re-appearance of parental characters in the second generation
of the offspring. Taking Naudin's idea of segregation or "dis-
junction" of the elements of the species, he concludes as follows:

"if . . . pollen which included the elements of one species happened
to unite with ovules including the elements of the other species the
intermediate or hybrid state would still be retained, and there would be
no reversion. But it would, as I suspect, be more correct to say that the
elements of both parent-species exist in every hybrid in a double state,
namely, blended together and completely separate." (italics inserted.)
(ic, 2:23)

The above comes very near to being a scientific statement of
the actual condition of things in a hybrid plant or animal. It is,
in fact, the closest to a correct expression of the true condition
in the heterozygote, of anything outside of Mendel's own writings.

According to Darwin's theory of "pangenesis," every cell in
the body was supposed to throw off small particles known as
"gemmules," which carried the characters to the reproductive
cells. In a hybrid, Darwin assumes that there are two kinds of
"gemmules" or character-carriers, pure gemmules coming from
each of the two parents, and combined or hybridized gemmules
as well. In the following statements Darwin then proceeds to
give, from his standpoint, as clear an account as could be de-
manded of the cause for the re-appearance of the original par-
ental characters.

"when two hybrids pair, the combination of pure gemmules derived
from the one hybrid with the pure gemmules of the same parts derived

PLANT HYBRIDIZATION BEFORE MENDEL 239

from the other would necessarily lead to complete reversion of charac-
ter; and it is perhaps not too bold a supposition that unmodified and
undeteriorated gemmules of the same nature would be especially apt to
combine." (ic, 2:383.) (Italics inserted.)

This statement approximates toward an explanation of what is
understood to occur when two F^ hybrids are mated. The re-
union of, say, character-unit or determiner D from the male with
D from the female gives DD, which reconstitutes one of the
original parents with respect to a character which breeds true;
and this is what we now understand "reversion" to be — the res-
toration in stable form of characters disunited and scattered or
"segregated" 'n the offspring of a cross.

Continuing, Darwin says :

"Pure gemmules in combination with hybridized gemmules would lead
to partial reversion. And lastly, hybridized gemmules derived from both
parent-hybrids would simply reproduce the original hybrid form. All
these cases and degrees of reversion incessantly occur, ic, 2:383.) (Italics
inserted.)

The above is an attempt at a statement of the conditions of
things in the heterozygous or hybrid condition except that "hy-
brid gemmules," or their equivalents, are not believed to exist as
such, and the crossing of the F^ with itself yields, of course, not
all "hybrids" as Darwin supposed, but leaves only one-half the
offspring in the hybrid condition. In the simple Mendelian hybrid
it has been found, to be sure, that, in addition to the parental
character-types being reproduced pure — i.e., 25 per cent of each —
one-half, or 50 per cent, of the individuals in the second genera-
tion reproduce again the hybrid form, owing to the factors not
being united with their like, but with, as it were, unlike factors,
or as it may be the absence of the factor in the opposite parent.
However, there are often modifying factors which do come in
from the other parent; at all events, the result is oftentimes a
dilution of the original character. Assuming the "hybridized"
gemmules to represent the "Dr" condition, we have in Darwin's
statement what is an approximation towards genetic language. In
other words, Darwin's theoretical statement comes rather close to
representing the Mendelian point of view in regard to the mating
of hybrid organisms of the F^ generation.

It seems strange indeed that with Darwin's instinct for detail,
and the acuteness and accuracy of his sense of observation, it
did not occur to him to studv the nature of hvbrids in the same

240 PLANT HYBRIDIZATION BEFORE MENDEL

manner that Mendel adopted, viz., by finding out the numerical
relations of the different kinds of character-types among the prog-
eny, and by formulating some law or principle to explain their
ratios. However, it is a matter of interest that Darwin, in the ab-
sence of actual experiments in point, should have come as close
as he actually did to finding an approximation toward a correct
theoretical explanation of what occurs in the cells of hybrids.

Darwin's theory was a natural corollary to his doctrine of
pangenesis. It is perhaps strange that, after the publication of
Naudin's idea of disjunction, and especially after the phenomenon
of segregation in peas had been noticed by five observers, all of
whose experiments Darwin remarks upon, Darwin himself did not
anticipate, in part at least, Mendel's actual experiment. How-
ever, it is a matter of special interest that a priori, in the absence
of experimental data, he should have come as close to the prin-
ciple of the Mendelian explanation as the above passages seem to
indicate.

BIBLIOGRAPHY

Darwin, Charles.

(a) The origin of species by means of natural selection, or
the preservation of favoured races in the struggle for
life. London, 1859; 6th ed.. New York, 1885.

(b) The effects of cross and self-fertilization in the vege-
table kingdom. New York, 1877.

Sageret, Augustin.

(a) Considerations sur la production des hybrides, des vari-
antes, et des varietes en general, et sur celles des Cucur-
bitacees en particulier. Annales des Sciences Naturelles.
18:294-314.

(b) Memoire sur les Cucurbitacees.

CHAPTER VIII

THE WORK OF FRANCIS GALTON

30. Sir Francis Galtoris Investigations in Heredity.

DURING the period from 1865 to 1900, one of the great-
est contributors to the theory of heredity was Sir Francis
Galton, and his investigations deserve to be reported with
clearness and in some detail, partly because the nature of his ex-
periments and their results are not always entirely understood,
and partly also because of a popular misconception of the nature
and applicability of his "law."

In 1889 appeared Galton's famous book on "Natural Inheri-
tance" (2a), which should be specially noted, inasmuch as it con-
stituted the first deliberate attempt since Quetelet's publications
(1832-1846-1848-1871), dealing with anthropometric measure-
ments, to marshal vital statistics into a series in such a form as
to show the laws governing heredity in populations, in respect to
such matters as stature, eye-color, artistic faculty, and disease,
since these involve Galton's well-known "Law of Regression," and
consist in the application of mathematical principles to the statis-
tical data of inheritance. Inasmuch as this was the most thorough
and extensive attempt at the development of a law of heredity
upon a mathematical basis appearing prior to the re-discovery of
Mendel's papers in 1900, it calls for consideration herein.

Galton calls attention to the fact that the faculties of men may
be roughly sorted into those that are natural and those that are
acquired, and proposes dealing with the former class.

Galton is noteworthy, in his day, for calling attention to the

particulate nature of inheritance. It is interesting to quote his

words :

"All living beings are individuals in one aspect, and composite in
another. They are stable fabrics of an inconceivably large number of
cells, each of vv^hich has, in some sense, a separate life of its own, and

242

PLANT HYBRIDIZATION BEFORE MENDEL

which have been combined under influences that are the subjects of much
speculation, but are as yet little understood. We seem to inherit bit by
bit, this element from one progenitor, that from another, under condi-
tions that will be more clearly expressed as we proceed, while the several

Plate XL. Sir Francis Galton, 1822-1911.

PLANT HYBRIDIZATION BEFORE MENDEL 243

bits are themselves liable to some small change during the process of
transmission. Inheritance may therefore be described as largely if not
wholly 'particulate,' and as such it will be treated in these pages." (2a,

P- 7-)

"We appear, then, to be severally built up out of a host of mmute

particles, of whose nature we know nothing, any one of which may be
derived from any one progenitor, but which are usually transmitted in
aggregates, considerable groups being derived from the same progeni-
tor. It would seem that while the embryo is developing itself, the par-
ticles, more or less qualified for each new post, wait as it were in com-
petition to obtain' it. Also that the particle that succeeds must owe its
success partly to accident of position and partly to being better qualified
than any equally well-placed competitor to gain a lodgment." (2a, p. 9.)

It is the latter conception that was concretely exemplified in
Mendel's principle of dominance, to which it appears that Galton
offered no corresponding hypothesis. Galton, however, recog-
nized the existence of "heritages that blend," and "heritages that
are mutually exclusive." For the former he cites the case of human
skin color, referring to crosses between the white and the negro,
adding :

"it need be none the less 'particulate' in its origin, but the result may
be regarded as a fine mosaic too minute for its elements to be distin-
guished in a general view." (ib., p. 12.)

It appears that the conception of "particulate inheritance" in-
terested Galton, since the quality of his mind was such as to de-
mand concrete expressions for the interpretation of inheritance
phenomena. The facts indeed increasingly appear to show "that
much so-called "blended inheritance" is actually particulate in
character.

As an example of "heritages that come altogether from one
progenitor to the exclusion of the rest," he cites eye-color.

"Eye-colour," he says, "is a fairly good illustration of this, the chil-
dren of a light-eyed and of a dark-eyed parent being much more apt to
take their eye-colours after the one or the other than to have inter-
mediate and blended tints." (ib., p. 12.)

Galton recognized the existence of "latent" characters.

"The total heritage of each man must include greater variety of ma-
terial than was utilized in forming his personal structure. [2a, p. 18.]
The existence in some latent form," he says, "of an unused portion is
proved by his power already alluded to, of transmitting ancestral char-
acters that he did not personally exhibit. Therefore the organized struc-
ture of each individual should be viewed as the fulfillment of only one
out of an indefinite number of mutually exclusive possibilities. His
structure is the coherent and more or less stable development of what

244 PLANT HYBRIDIZATION BEFORE MENDEL

is no more than an imperfect sample of a large variety of elements."
{ib., p. 18.)

Galton, in the absence of the chromosome theory of the inheri-
tance of what he calls the "elements" or "particles" of the poten-
tial heritage, undertakes to classify the "imperfect sample of a
large variety of elements," under three possible categories : first,
the conception embodied in Darwin's theory of pangenesis ; sec-
ondly, "that of a more or less general co-ordination of the influ-
ences exerted on each element, not only by its immediate neigh-
bours, but by many or most of the others as well," and finally,
that of "accident or chance, under which name a group of agencies
are to be comprehended, diverse in character and alike only in
the fact that their influence on the settlement of each particle
was not immediately directed towards that end." {ib.^ p. 19.)

Galton proposes the idea that the particulate nature of inheri-
tance makes it appear that there is really

". . . no direct hereditary relation between the personal parents and
the personal child," but "that the main line of hereditary connection
unites the sets of elements out of which the personal parents had been
evolved with the set out of which the personal child was evolved. The
main line may be rudely likened to the chain of a necklace, and the per-
sonalities to pendants attached to its links. We are unable to see the
particles and watch their grouping, and we know nothing directly about
them, but we may gain some idea of the various possible results by not-
ing the differences between the brothers in any large fraternity . . .
whose total heritages must have been much alike, but whose personal
structures are often very dissimilar." {ib., pp. 19-20.)

In a discussion which follows as to the nature of stability in
the inheritance of the organism, Galton makes a hypothetical sug-
gestion as to the behavior in inheritance, or the nature of the
hereditary factors concerned.

"The changes," he says, "in the substance of the newly fertilized ova
of all animals . . . indicate segregations as well as aggregations, and
it is reasonable to suppose that repulsions concur with affinities in pro-
ducing them. We know nothing as yet of the nature of these affinities
and repulsions, but we may expect them to act in great numbers and on
all sides in a space of three dimensions. . . . Every particle must have
many immediate neighbours. . . . We may therefore feel assured that
the particles which are still unfixed must be affected by very numerous
influences acting from all sides and varying with slight changes of place,
and that they must occupy many positions of temporary and unsteady
equilibrium, and be subject to repeated unsettlement, before they finally
assume the positions in which they severally remain at rest." {ib.,
pp. 20-1.)

PLANT HYBRIDIZATION BEFORE MENDEL 245

Galton effectively combats the very general view that natural
selection proceeds only through small steps,

". . . for which," he says, "it is difficult to see either the need or the
justification, namely, that the course of evolution always proceeds by
steps that are severally minute, and that become effective only through
accumulation," {ib., p. 32.)

"That the steps may be small and that they must be small are very dif-
ferent views; it is only to the latter that I object, and only that the in-
definite word 'small' is used in the sense of 'barely discernible,' or as
small compared with such large sports as are known to have been the
origins of new races." {ib., p. 32.)

Galton then points out that an apparent ground for this com-
mon belief lies in the fact that when intergrading forms are looked
for, whether in the case of plants, animals, language-forms, weap-
ons, utensils, or any other evolutionary product:

"A long and orderly series can usually be made out, each member of
which differs in an almost imperceptible degree from the adjacent speci-
mens [p. 32]. But," he says, "it does not at all follow, because these
intermediate forms have been found to exist, that they are the very
stages that were passed through in the course of evolution. Counter-
evidence exists in abundance, not only of the appearance of considerable
sports, but of their remarkable stability in hereditary transmission." {ib.,
P- 32.)

Galton's ruling conception in dealing with the question of
heredity was, as is well known, to proceed by the method of de-
duction from the law of averages, as demonstrated by popula-
tions. Herein we see the prevalent misconception of his day, so
far as the investigation of individual inheritance is concerned —
that of predicting the behavior of the individual upon the basis of
the law of probability, as demonstrated by the outcome or product
of generations of like populations.

"The science of heredity," he says, "is concerned with Fraternities and
large Populations rather than with individuals, and must treat them as
units." (p. 35.)

The greater portion of Galton's "Natural Inheritance" is de-
voted to the discussion of anthropometric data collected upon the
subject of stature, eye-color, artistic faculty, and disease. His bio-
metric observations were, however, originally made upon sweet
peas. He states :

"l had to collect all my data for myself, as nothing existed, so far as
I know, that would satisfy even my primary requirement. This was to
obtain records of at least two successive generations of some population
of considerable size. They must have lived under conditions that were

246 PLANT HYBRIDIZATION BEFORE MENDEL

of a usual kind, and in which no great varieties of nature were to be
found. Natural selection must have had little influence on the charac-
teristics that were to be examined. These must be measurable, variable,
and fairly constant in the same individual. The result of numerous in-
quiries, made of the most competent persons, was that I began my ex-
periments many years ago on the seeds of sweet peas. . . ." (p. 71.)

At first both size and weight were determined but, after becom-
ing assured of the equivalence of the two methods, Galton con-
fined himself to the weights, in that they were more easily ascer-
tained than the measurements.

"It is more than 10 years (from 1889) since I procured these data.
They were the result of an extensive series of experiments on the pro-
duce of seeds of different sizes, but of the same species, conducted for
the following reasons. I had endeavoured to find a population possessed
of some measurable characteristic that was suitable for investigating the
causes of the statistical similarity between successive generations of a
people." (p, 80.)

As to the selection of sweet peas, Galton says :

"They do not cross-fertilize, which is a very exceptional condition
among plants ; they are hardy, prolific, of a convenient size to handle,
and nearly spherical ; their weight does not alter perceptibly when the
air changes from damp to dry, and the little pea at the end of the pod,
so characteristic of ordinary peas, is absent in sweet peas." (p. 80.)

Seven sets were selected for planting, containing ten seeds
each, graduating in weight from the heaviest to the lightest.

After speaking of the immense amount of labor involved in
the details of the experiment, Galton says :

"The results were most satisfactory. They gave me two data, which
were all that I wanted in order to understand, in its simplest approxi-
mate form, the way in which one generation of a people is descended
from a previous one ; and thus I got at the heart of the problem at
once." (p. 82.)

The tabulated results of this work upon the weights of seeds in
two succeeding generations of sweet peas were such as to demon-
strate what Galton called the fact of filial regression.

"It will be seen," he says, "that for each increase of one unit on the
part of the parent seed, there is a mean increase of only one-third of a
unit in the filial seed ; and again that the mean filial seed resembles the
parental when the latter is about 15.5 hundredths of an inch in diameter.
Taking 15.5 as the point towards which Filial Regression points, what-
ever may be the parental deviation from that point, the mean Filial
Deviation will be in the same direction, but only one-third as much."
(p. 225.)

In the investigation of the inheritance of human stature. Gal-

PLANT HYBRIDIZATION BEFORE MENDEL 247

ton states his reasons for selecting it as a subject for the investi-
gation of heredity.

"Some of its merits are obvious enough, such as the ease and frequency
with which it may be measured, its practical constancy during thirty-five
or forty years of middle life, its comparatively small dependence upon
differences of bringing up, and its inconsiderable influence on the rate
of mortality." (p. 83.)

"other advantages not equally obvious are equally great. One of these
is the fact that human stature is not a simple element but a sum of the
accumulated lengths or thicknesses of more than a hundred bodily parts."
(pp. 83-4.)

"The beautiful regularity in the Statures of a population, whenever
they are statistically marshalled in the order of their heights, is due to
the number of variable and quasi-independent elements of which Stature
is the sum." (p. 85.)

The data for stature and the other human characters observed
were obtained from the "Records of Family Faculties," amounting
to 150 families in all, from which Galton extracted data as to the
stature of 205 couples of parents, as compared with a total of
930 of their adult children of both sexes. For purposes of calcula-
tion, Galton introduced the theoretical "mid-parent,"

". . . an ideal person of composite sex, whose Stature is halfway between
the Stature of the father and the transmuted Stature of the mother."
(p. 87.)

The transmutation for female stature was stated as follows :

"The artifice is never to deal with female measures as they are ob-
served, but always to employ their male equivalent in the place of them.
I transmute all the observations of females before taking them in hand,
and thenceforth am able to deal with them on equal terms with the ob-
served male values. For example : the statures of women bear to those
of men the proportion of about twelve to thirteen. Consequently by
adding to each observed female stature at the rate of one inch for every
foot, we are enabled to compare their statures, so increased and trans-
muted, with the observed statures of males on equal terms." {ib., p. 6.)

As a result of these data, Galton concluded that:

"The filial deviation from P (the mid-stature of the population, 68j^
inches), is, on the average, only two-thirds as wide as the Mid-Parental
Deviation. I call this ratio of 2 to 3 the "ratio of 'Filial Regression.' It is
the proportion in which the Son is, on the average, less exceptional than
his Mid-Parent." (p. 97.)

"This value of two-thirds will therefore be accepted as the amount of
regression, on the average in many cases, from the mid-parental to the
mid-filial stature whatever the mid-parental stature may be." (p. 98.)

Galton discusses the practical effects of the law of regression
thus :

248 PLANT HYBRIDIZATION BEFORE MENDEL

"The law of regression tells heavily against the full hereditary trans-
mission of any gift. Only a few out of many children would be likely
to differ from mediocrity so widely as their mid-parent, and still fewer
would differ as widely as the more exceptional of the two parents. . . ."
(p. 106.)

"It must be clearly understood that there is nothing in these statements
to invalidate the general doctrine that the children of a gifted pair are
much more likely to be gifted than the children of a mediocre pair.
They merely express the fact that the ablest of all the children of a few
gifted pairs is not likely to be as gifted as the ablest of all the children
of a very great many mediocre pairs." (p. 106.)

From the data obtained, Galton undertook to calculate the value
of the respective contributions of the successively ascending an-
cestors to the inheritance.

"if D is the stature of the mid-parent, then mid-parents whose stature
is P D have children whose average stature is P 2/3 D. In other words,
a character in a man implies a character of 1/3 of that amount in his
mid-parent. Likewise the character in the mid-parent of the man being D,
the same character in the mid-parent of the mid-parent would be 1/3 D,
that of the mid-great-grandparents 1/9 D, and so on. Hence the total
inheritance would be represented by D (i + i/3+l/9+&c.)=D 3/2."

(P- 134-)

By theoretical calculations (p. 13^) Galton arrives, from two
different directions, at the figures 4/9 and 6/11, respectively, as
representative values for the extent to which the mid-parents'
characters are represented in, or, as he says, "influence" the off-
spring. These values, 44/99 and 54/99, as he says, "differ but
slightly from 1/2, so we may fairly accept that as the result."

"Hence the influence, pure and simple, of the mid-parent may be
taken as 1/2, and that of the mid-grandparent as 1/4, and of the individ-
ual grandparent 1/16, and so on. It would, however, be hazardous, on the
present basis, to extend this sequence with confidence to more distant
generations." (p. 136.)

With respect to the inheritance of eye-color, Galton makes com-
ment as follows :

"stature and eye-colour are not only different as qualities, but they are
more contrasted in hereditary behaviour than perhaps any other common
qualities. Parents of different statures usually transmit a blended inheri-
tance to their children, but parents of different eye-colours usually trans-
mit an alternative heritage, if one parent is as much taller than the
average of his or her sex as the other parent is shorter, the stature of
their children will be distributed, as we have already seen, in nearly
the same way as if the parents had both been of medium height. But if
one parent has a light eye-colour, and the other a dark eye-colour, some
of the children will, as a rule, be light and the rest dark; they will

PLANT HYBRIDIZATION BEFORE MENDEL 249

seldom be medium eye-coloured, like the children of medium eye-
coloured parents." (p. 139.)

"if notwithstanding this two-fold difference between the qualities of
stature and eye-colour, the shares of hereditary contribution from the
various ancestors are alike in two cases, as I shall expect to show that
they are, we may with some confidence expect that the law by which
those hereditary contributions are found to be governed may be widely
and perhaps universally applicable." (p. 139.)

The data for eye-color were drawn from the same collection of
family records referred to for the data for statures. Taking the
fraternities in which the eye-color is known for the two parents
and the four grandparents, there are 211 of such groups, with a
total of 1,023 children. Letting S stand for the individual subject
of the investigation, F for the parent of the individual, G^ for his
grandparent, Go for his great-grandparent, etc., the transmission
to the individual is F, 1/4; G^, 1/16; Go, 1/64; etc.

Supposing that the amount of any peculiarity possessed by F
is equal to D, then, as Galton has shown, each of the immediate
ancestors of F, who stand in the relation of G^ to S, will on the
average possess 1/3 D. Similarly, each of the four grandparents
of F (who stand in the order of Go to S) will, on the average,
possess 1/9 D and so on. Now F transmits to S only 1/4 of his
inherited peculiarity; G^ transmits only 1/16; Go only 1/64 and
so on. Hence the aggregate total of the inheritance of any peculi-
arity in the heritage that may be expected in S is as follows:

D^ i/4+2(i/3Xi/2^)+4(i/9Xi/2'^)+&c. [ =

I J

D(i/22+i/23.3+i/2M-+&c.)=DX0.30

where the eye-colors of the two parents are given.

This means that each parent must contribute 0.30 to the heri-
tage of the offspring in question, or the two parents taken to-
gether, 0.60, leaving a residue of O.40 due to the influence of an-
cestry about which nothing is known or implied.

By a similar calculation Galton shows that the aggregate of
the probable heritages from G^ are expressed by DX0-l6
(0.1583), where the eye-colors are given of the four grand-
parents. Similarly, where the eye-colors are given of the two par-
ents and four grandparents, the aggregate contribution of each
grandparent is DX3/40=DXO-075, taken as 0.08.

250 PLANT HYBRIDIZATION BEFORE MENDEL

In Tables 19 and 20 (pp. 215-16), the observed and the cal-
culated eye-colors are given for 16 groups of families, in which

". . . those families are grouped together in whom the distribution of
light, hazel, and dark eye-colour among the parents and grandparents
is alike. Each group contains at least twenty brothers or sisters." (p. 215.)

The correctness of the calculations, as compared with the ob-
served data, are well shown, as Galton remarks, by the totals in
Table 19, in which the aggregate calculated number of light-eyed
children, under Groups I, II, III, are given as 623, 601, and 614,
respectively, while the observed numbers were 629, being correct,
therefore, in the ratio of 99, 96, and 98 to 100.

Galton concludes his observations on the subject of eye-color
as follows :

"My returns are insufficiently numerous and too subject to uncertainty
of observation, to make it worth while to submit them to a more rigorous
analysis, but the broad conclusion to which the present results irresistibly
lead is that the same peculiar hereditary relation, that was shown to
subsist between a man and each of his ancestors in respect to the quality
of stature, also subsists in respect to that of eye-colour." (p. 153.)

No attempt will be made to discuss the data and calculations
with respect to inheritance of artistic faculty and of disease.

Sufficient has been presented to show the mode of operation of
Galton's mind in respect to the matter of inheritance. It suffices
to say, that Galton's work constituted the first considerable at-
tempt at an exact analysis of hereditary data upon a mathe-
matical basis, during the pre-Mendelian period. The fact that his
data do not constitute a genetic analysis, but a statistical state-
ment of the general result in respect to populations, does not de-
tract from their absolute value, or from their correctness from the
standpoint of the operation of the law of averages upon popu-
lations, where the data for several generations are properly
grouped and classified as a whole.

In 1897 (2b) Galton contributed to the Proceedings of the
Royal Society (Vol. 61, pp. 401-13, June 3, 1897), a brief memoir
constituting the continuation of his investigation upon the law of
ancestral inheritance reported in his "Natural Inheritance" of
1869, the material from which the memoir was derived being
the pedigree records of the well-known Basset hounds of Sir
Everett Millais. The paper in question is entitled, "The average

PLANT HYBRIDIZATION BEFORE MENDEL 251

contribution of each several ancestor to the total heritage of the
offspring."

In this contribution Galton remarks that the truth of the sta-
tistical law of heredity, which had been stated "briefly and with
hesitation" in his "Natural Inheritance," because "it was then
unsupported by sufficient evidence," having been now found to
hold for a particular case, there are, as he says, "strong grounds
for believing it to be a general law of heredity." (p. 401). Gal-
ton at first in this connection, began "a somewhat extensive series
of experiments with moths," which, however, failed owing to the
diminishing fertility of successive broods, and the disturbing ef-
fects of differences in food and environment. Consequently, as he
says, "no statistical results of any consistency or value could be
obtained from them." (p. 402.) While engaged in planning an-
other extensive experiment with small, fast-breeding mammals,
Galton

". . . became acquainted with the existence of a long series of records,
preserved by Sir Everett Millais, of the colours during many successive
generations of a large pedigree stock of Basset hounds, that he origi-
nated some twenty years ago, having purchased ninety-three of them on
the continent for the purpose. These records afford the foundation upon
which this memoir rests." (p. 402.)

The "law," as briefly stated is,

". . . that the two parents contribute between them on the average,
one-half or (0.5) of the total heritage of the offspring ; the four grand-
parents, one-quarter or (0.5)-, the eight great-grandparents one-eighth
or (0.5)"*, etc., which being equal to l, accounts for the whole heritage."
(p. 402.)

"The same statement may be put into a different form, in which a
parent, grandparent, etc., is spoken of without reference to sex, by say-
ing that each parent contributes on an average, one-quarter or (0.5)^,
each grandparent one-sixteenth or (0.5)'*, and so on, and that generally
the occupier of each ancestral place in the nth degree, whatever be the
value of n, contributes (0.5)^" of the heritage." (p. 402.)

Galton refers to sex-limited inheritance, although not precisely
in the manner now current, in the following statement:

"The neglect of individual prepotencies is justified in a law that avow-
edly relates to average results ; they must, of course, be taken into ac-
count when applying the general law to individual cases. No difficulty
arises in dealing with characters that are limited by sex, when their
equivalents in the opposite sex are known, for instance in the statures of
men and women." (p. 402.)

252 PLANT HYBRIDIZATION BEFORE MENDEL

That Galton undertook in a way to conceive of the genotype as
the object of his research, is shown by the following statement:

"It should be noted that nothing in this statistical law contradicts the
generally accepted view that the chief, if not the sole, line of descent
runs from germ to germ and not from person to person. The person may
be accepted on the whole as a fair representative of the germ, and, that
being so, the statistical laws which apply to the persons would apply
to the germs also, though with less precision in individual cases."

(p. 403-)

As an a priori argument for reasonableness of the law, Galton

says :

". . . there is such a thing as an average contribution appropriate to
each ancestral place, which admits of statistical valuation, however min-
ute it may be. It is also well known that the more distant stages of an-
cestry contribute considerably less than the nearer ones. Further, it is
reasonable to believe that the contributions of parents to children are in
the same proportion as those of the grandparents to the parents, of the
great-grandparents to the grandparents, and so on ; in short, that their
total amount is to be expressed by the sum of the terms in an iafinite
geometric series diminishing to zero. Lastly, it is an essential condition
that their total amount should be equal to i, in order to account for the
whole of the heritage. All these conditions are fulfilled by the series of
/^> V2, Vz, etc., and by no other. These and the foregoing considerations
were referred to when saying that the law might be inferred with con-
siderable assurance a priori : consequently, being found true in the par-
ticular case about to be stated, there is good reason to accept the law in
a general sense." (p. 403.)

As to the material of the investigation — the Basset hounds
referred to — they were dwarf blood-hounds, showing but two
color variations; one white with large blotches ranging between
red and yellow, registered as "lemon and white" ; another with
the above coloration plus more or less black, called "tricolour."
Galton says :

"Tricolour is, in fact, the introduction of melanism, so I shall treat
the colours simply as being 'tricolour' or 'non-tricolour' ; more briefly as
T or N. I am assured that transitional cases between T and N are very
rare, and that experts would hardly ever disagree about the class to
which any particular hound should be assigned." (p. 403.)

For his purposes, Galton made use of "The Basset Hound Club
Rules and Stud Book," compiled by Sir Everett Millais, compris-
ing the pedigree records of the hounds in question from 1874 to
1896, and containing the names of nearly 1,000 animals.

Out of these, Galton obtained a series of 817 hounds of knov/n
color, descended from parents of known color. In 567 cases out

PLANT HYBRIDIZATION BEFORE MENDEL 253

of the 817, the colors of all four of the grandparents were also
known.

"The upshot is," he says, "that I have had the good fortune to discuss
a total of 817 hounds of known colour, all descended from parents of
known colour. In 567 out of the 817, the colours of all four of the grand-
parents are also known; in 188 of the latter, in turn, the colours of all
eight great-grandparents were also known." (p. 404.)

Gal ton's remarks with reference to his effort to find a lule that
would apply with respect to what might be presumed to be sex-
linked inheritance, or as it was then called sex-prepotency, are
interesting as showing the manner in which it was possible to
arrive at conclusions upon this point by means of the statistical
method.

"Our first inquiry then must be, 'is or is not one sex so markedly pre-
potent over the other in transmitting colour, that a disregard of sex
would introduce statistical error*?' In answering this, we should bear in
mind a common experience, that statistical questions relating to sex are
very difficult to deal with." Large and unknown disturbing causes ap-
pear often to exist, that make data that are commonly homogeneous very
heterogeneous in reality. "Some of these are undoubtedly present here,
especially such as may be due to individual prepotencies combined with
close interbreeding. . . ."

The results were derived from two classes of data ; one, derived
from individuals of which all the grandparents were known,
amounting to 567 individuals ; the other, of which all the grand-
parents were not known, amounting to 250 individuals. These
data, as Galton states,

". • . will be seen to disagree widely, concurring only in showing that
the dam is prepotent over the sire in transmitting colour."

Taking the data from the two respective classes separately, the
former, called the "A" data, gave relative prepotency as 58:51,
or 114: 100. The second set, or the "B" data, gave a relative ratio
of prepotency as 47 : 32 or 147 : 100. Taken together, the data give
a combined ratio of 54:45 or of 120:100, i.e., as 6 is to 5. (pp.
404-5.)

It was found that a certain amount of preferential activity
took place, exhibited by the tendency to use tricolors as sires,
so that reciprocal matings were not equally numerous. "Still,"
Galton remarks, "on the application of a general test, the error
feared is too insignificant to be observed." (p. 405.)

254 PLANT HYBRIDIZATION BEFORE MENDEL

It is interesting to note that Galton endeavors by means of his
statistical method to arrive at a conclusion concerning what he
termed sex-prepotency, and that he recognized the fact that some
single character, color in this case, might operate in a special
manner in the inheritance.

Galton's manner of calculating the influence of the tricolor
factor is interesting. He found from the data that 79 per cent of
the parents of tricolor hounds were tricolor also, and that 56 per
cent of the parents of non-tricolor hounds were tricolor. Suppos-
ing all the four grandparents, A2, to be tricolor, then only 0.79
per cent of A3 will be tricolor also; (0.79)" of A^ and so on. The
several degrees of ancestry will respectively contribute an average
of tricolor to each ao, amounting to (o.^)^y((o.jg)-\-( i-\-(o.^)
X(o.79) + (o.5)-X(o.79)-+etc.)=o.i632. His conclusion there-
fore is that the average tricolor contribution from the ancestry
of each of the four tricolor grandparents will be equal to one-
fourth of this, viz., 0.0408.

Similarly, the average tricolor contribution from the ancestry
of each non-tricolor grandparent is found to be O.0243. When the
furthest generation known is that of the great-grandparents, the
formula differs from the preceding only by substituting (0.5)'* X
(0.79) for (o.5)"X (0.79). Thus the average tricolor contribu-
tion from the total of the eight tricolor great-grandparents is
found to be O.0816, and the contribution from each of them
0.0102. Similarly the contribution from each non-tricolor great-
grandparent is found to be 0.0061.

On the same basis of these calculations, and taking the number
of tricolors in the parents in the classes of 2, 1, and o, respec-
tively, and the number of tricolors in the grandparents as 4, 3,
2, and 1, respectively, Galton was able to calculate coefficients
for tricolor occurrence in the offspring. Thus, taking the case of
tricolor in both the parents, combined with tricolors in 4, 3, 2,
and 1 of the grandparents, respectively, the multiplying co-
efficients are found to be as follows: 0.91, 0.83, 0.76, and 0.68.
Multiplying the number of cases, 119, 119, 28, and 11 in the
four categories, by the four respective coefficients, gives the cal-
culated numbers of the tricolor offspring as 108, 99, 21, and 8,
respectively. How closely this calculation fitted the actual cases,
is proved by the fact that the observed tricolor cases in the off-

PLANT HYBRIDIZATION BEFORE MENDEL 255

spring in question, for the four categories of 4, 3, 2, and 1 tri-
color grandparents with both parents tricolor, was 106, lOl, 24,
and 8, respectively. The correspondence between the calculated
result and the observed numbers, in the case where one parent
only was tricolor, and where neither was tricolor, was equally
close. The calculations made in a similar manner, where the num-
ber of tricolors in the great-grandparents was 8, 7, 6, 5, and 4,
respectively; in the grandparents, 4, 3, and 2, respectively, and
in the parents 2 and 1, respectively, showed an equally remark-
able close correspondence between the calculated results and the
observed facts.

For example, where the tricolors in the great-grandparents
were, 7, 6, 5, and 4, respectively, the number of tricolors in
grandparents 3, and the number in the parents 2, the relation
between the calculated and the observed facts in the four cases
was found to be 16 : 17, 18 : 19, 13 : 14, and 5:6, respectively. The
summary of all cases gave the relation of calculated to observed
tricolor in the offspring as 180:181.

It would thus appear that the contribution of the immediate
ancestors to the color-inheritance, theoretically and experimen-
tally, would be as follows :

Parents each O.2500

Grandparents (tricolor, calculated) each 0.0625

Grandparents (tricolor, experimental) ' each 0.0408

Grandparents (non-tricolor, experimental) each O.0243

Using these particular coefficients as components of value. Gal-
ton constructed a general coefficient to express each set of com-
binations of tricolor and non-tricolor, found in the hounds' an-
cestry. The cases are as follows, using "T" for tricolor and "N"
for non-tricolor.

The letters represent all possible combinations of tricolor "T,"
and non-tricolor "N," according as^they occur in the different
cases, each pair of letters representing a pair of grandparents,
paternal and maternal.

Case I ,

TT-TT

Here all four of the grandparents of the tricolor animals were

256

PLANT HYBRIDIZATION BEFORE MENDEL

tricolor also. The condition of the ancestry then, in terms of the
partial values of the ancestor's contribution is :

2 parents

4 grandparents (tricolor, calculated)

4 grandparents (tricolor, experimental)

each 0.2500 0.5000
each 0.0625 0.2500
each 0.0408 0.1632

0.9132

Case II
TT.TN TN.TT TT.NT NT.TT

2 parents

3 grandparents (tricolor, calculated)

3 grandparents (tricolor, experimental)

1 grandparent (non-tricolor, experimental)

each

0 . 2500

?0O0

each

0.0625

1875

each

0.0408

1224

each

0.0243

0243

0.8342

Case III
TN.TN TT.NN TN.NT NT.TN NN.TT NT.NT

2 parents

2 grandparents (tricolor, calculated)

2 grandparents (tricolor, experimental)

2 grandparents (non-tricolor, experimental)

each 0.2500

each 0.0625

each 0.0408

each 0.0243

2000
1250
0816
0486

0.7552

Case IV

TN.NN NN.TN NT.NN NN.NT

2 parents each 0.2500 0.5000
1 grandparent (tricolor, calculated) each 0.0625 0.0625
1 grandparent (tricolor, experimental) each 0.0408 0.0408

3 grandparents (non-tricolor, experimental) each 0.0243 0.0729

0.6761

Thus, taking the total number of tricolor cases up to the second
descending generation, and multiplying by the respective co-
efficients of each, the relation of the total sum number of tricolor
offspring calculated, to those observed, was as 391 .'387. The
data are given in detail in the following table, somewhat re-
arranged from Galton. In each instance, the coefficient, multiplied
by the number of cases, gives the theoretical or calculated num-
ber erf tricolor animals out of the total (the underscored number).
Beneath the figure of each case, is given the actual observed num-
ber of tricolors.

h-l
o
y

i-i
<.

(Zl

(/3

h-!
<

CO
M

00
CO

Ph
Q

-H doooo

00 d - Tf

CO
VO d CO ''t

vo d

-< <s

O ^
CO CO

00 d «^ r>.

PC
O

i-l

o
o

H
in

CO
00

— o^ o

cr\ o 00 *>o
- o o

00 d

t^ d

Tj- o

•73

>■
u

I— I t'5

o o

(U ^H l-H

•-H o O

o tg o O

O o I-I "-I

^ U h H

•'"N

^ )

C/3

c«

4-1

■s*^

<-t-i

• ^H

. .— <

l-H

;-H

^ U h H

, ; w

a o

aj ii ii

°^ S 8

O o !-i t-"

^ u h h

1/3

258 PLANT HYBRIDIZATION BEFORE MENDEL

In like manner, where the pedigree reached up to the third
ascending generation, the total number of tricolor cases in the
offspring calculated, to those observed, was as 180 to 181. Thus
in both instances there was an almost perfect coincidence of the
observed data with the mathematical law.

Galton did not rest content with the obtained results :

"In order to satisfy myself," he says, "that the correspondence between
calculated and observed values was a sharp test of the correctness of
the coefficients, I made many experiments by altering them slightly, and
re-calculating. In every case there was a notable diminution in the ac-
curacy of the results. The test that the theory has successfully undergone
appeared on that account to be even more searching and severe than I
had anticipated." (p. 408.)

Galton was thus able to demonstrate the possibility of calculat-
ing, on a statistical basis, the probable number of offspring in a
given case of color-inheritance, in a manner that satisfied the re-
quirements of a statistical law of descent. The fact that Galton's
constituted the only attempt during the pre-Mendelian period, to
arrive at a fully exact and quantitative scientific method of at-
tacking the question of inheritance, renders it noteworthy, even
although the method is statistical rather than genetic in character.

Galton well sums up his views in words that are probably little
widely known, but that should be read, in order to realize that
the author of "Galton's Law" was not a mere mathematical ma-
chine, but a man of broad humanistic as well as utilitarian views.

"It is hardly necessary to insist on the importance of possessing a cor-
rect law of heredity. Vast sums of money are spent in rearing pedigree
stock of the most varied kinds, as horses, cattle, sheep, pigs, dogs, and
other animals, besides flowers and fruits. The current views of the breed-
ers and horticulturists on heredity are contradictory in important re-
spects, and therefore must be more or less erroneous. Certainly no pop-
ular view at all resembles that which is justified by the present memoir.
A correct law of heredity would also be of service in discussing actuarial
problems relating to hereditary longevity and disease, and it might throw
light on many questions connected with the theory of evolution."

As Goldschmidt says :

"of course the significance of a biological law disappears for the law
of ancestral heredity. All that it shows is that it can be taken as a statis-
tical consequence of Mendelian number-ratios when, in a mixed popula-
tion, the members of which propagate among themselves, average values
are regarded." (2, p. 62.)

Galton's Law has been thus fully treated because of its funda-

PLANT HYBRIDIZATION BEFORE MENDEL 259

mental character as a law of evolution, describing the average
trend of circumstances when a large number of individuals are
taken together without reference to sex. It is an expression of the
law of bodily appearances, and only pretends to describe the con-
dition in the germ cells, as Galton himself observes, insofar as
the bodily characteristics are the outward expression of an in-
ternal germinal condition, which Galton assumed, reasoning re-
versely, must be the case, else why should there be an average
inheritance of the color-characters of the nature described. How-
ever, Galton's expectation that his discovery might be available
for practical breeding purposes has not been entirely justified.
It has indeed proved the value of pedigree records for live stock,
and the general truth of the axiom that "like begets like." In a
word, in the light of our present understanding, "Galton's Law"
is largely an average mathematical expression for the operation
of the law of dominance. It is the most important effort, however,
during what may be called the "Darwinian period," at obtaining
an exact statistical expression of the law of inheritance in
populations.

BIBLIOGRAPHY

Galton^ Francis.

(a) Natural Inheritance. London and New York, 1889.

(b) The average contribution of each of several ancestors
to the total heritage of the offspring. Proc. Roy. Soc.
61 1401 . 1897.

Goldschmidt^ Richard.

Einfiihrung in die Vererbungs-wissenschaft. 4th ed., Leipzig,

1923-

CHAPTER IX

31. Miscellaneous Investigations on the Histological Structure of

Hybrids

THE contributions here under consideration, of Macfar-
lane, Henslow, Wilson, and Darbishire, are devoted largely
to the study of the details of the histological characters
of a considerable number of plants and of their hybrids in the
first generation. Although the work of the last-named investigator
came after the rediscovery of Mendel, the work of Darbishire on
peas is included because of the interest attaching to work with this
plant, and its relation to the general subject of Mendelism.

a. Henslow.

The paper of J. S. Henslow (5), "On the Examination of a
hybrid Digitalis," read November 14, 1831, and published in the
Transactions of the Cambridge Philosophical Society, 4:257-78
(1833), while minor in extent, was perhaps the first paper on
hybrids, since the publications of Sageret, which attempted to deal
with characters of the hybrid and of its parents from the com-
parative standpoint, and, to some extent, in terms of measure-
ment. It is certainly the first paper of the sort to appear in
English.

Henslow, while Professor of Botany at Cambridge University,
states that :

"chance having favored me with a hybrid Digitalis during the past
summer [1831], in my own garden, I employed myself, whilst it con-
tinued to flower, which was from June 19 to July 22, in daily examining
its character, and anatomizing its parts of fructification. I was careful to
compare my observations, with as much patience and accuracy as I can
command, with the structure of its two parents. It seemed to me not
unlikely that something interesting might result from a rigorous exami-
nation of this kind, or at least that its recorded details might serve as a
point of departure for future observations." (p. 257.)

The plant, according to Henslow (^), was a natural garden

cross between Digitalis lutea and D. purpurea. The seeds of each

Plate XLI. Digitalis lutea x purpurea; flowering organs and tissues of parents and
F^ hybrid, by J. S. Henslow.

262

PLANT HYBRIDIZATION BEFORE MENDEL

had been allowed to scatter, and the seedlings to grow wherever
they chanced to appear.

"I had already," he says, "remarked a singularity in the general ap-
pearance of one of these, and was watching the expansion of its flow-
ers, when I was agreeably surprised to find it a decided hybrid, obviously
having most of its characters exactly intermediate between those of pur-
purea and lutea. [p. 258.] . . . My plant exactly agrees in most particu-
lars with a hybrid procured by Kolreuter in 1768, from seeds of lutea fer-
tilized by the pollen of purpurea. (Acad. Petropol. Anno. 1777.)"

In general habit, Henslow's hybrid is stated to have approached
"much nearer lutea than purpurea^ (p. 258.)

"It is, however," he continues, "decidedly taller and more robust than
any specimens of the former species which my garden ever produced.
Kolreuter indeed asserts that the specimens raised by him were taller than
either of their parents, but he assigns a lower limit to the height of
purpurea than that to which many plants of this species have attained
with me."

On p. 258, Henslow gives an analysis of twenty-five characters
in root, stem, leaf, inflorescence, flower, stamens, and pistil, with
illustrative plates.

"a single glance of the eye," he says, "will thus be sufficient to show
how totally intermediate most of its organs are, both in size and form,
and in some cases also in colour, to those of the two parents." (p. 259.)

Attempts to fertilize the hybrid with its own pollen, as well
as with pollen of the two parents, failed, and the comment is made
that Kolreuter was similarly unsuccessful in his case. Some dis-
cussion is given as to whether hybrids are self-fertile or not. The
paper merits mention by reason of the fact that, if not the first,
it is one of the first attempts to present, in systematic detailed
form, a comparative study, in part microscopic, of the structures
in a hybrid and its two parents. A satisfactory scale is not given.
A few of the principal characters noted are given in the following
table :

External Characters

Root

Height of stem
Length of raceme
Leaves

D. purpurea
Biennial

3 to 5 ft.

\y2 in. to 3 ft.

Woolly

D. lutea
Bi-triennial

2 ft.

^ to 1 ^ ft.

Glabrous

Hybrid lutea X
purpurea

Apparently peren-
nial

About 3^ ft.

About 1^ ft.

Nearly smooth
above, quite
woolly below

PLANT HYBRIDIZATION BEFORE MENDEL

263

Flowers

Corolla

Spots on corolla

Anthers

D. purpurea
Large, cernuous

Purple

Numerous,
deep purple

Deeper orange-
yellow, with
numerous
spots, often
confluent

Hybrid lutea X
purpurea

Medium size, near-
ly horizontal

Yellow ground,
tinted with red

A few dark pur-
plish red spots
Lighter yellow, Yellow, inclining to
no spots orange, with a

few small, scat-
tered purplish
red spots

D. lutea

Small, more
drooping
Yellow

No spots

b. Marfarlane.

In the 90's of the last century, J. M. Macfarlane (6) published
considerable work based upon a histological study of the charac-
ters of hybrids and of their parents, which did much to throw
light upon the ultimate character of the hybrid condition in the
Fj generation. As the result of these investigations upon the his-
tological details of many hybrids and of their parents, Macfar-
lane was able to take a much more exact point of view regarding
the structural characters in hybrids than most of his contempo-
raries, one indeed for which few data then existed, and in which
investigation seems not to have been continued until the post-
Mendelian work of Darbishire (1), on the structure of the starch
grains in crosses of peas.

Macfarlane's work was first presented at the meeting of the
Edinburgh Botanical Society, March 1890, the first published con-
tribution being an article in the Gardeners' Chronicle for May 3
(6a). In this article he says:

"During the last few years I have studied minutely the general and
microscopic structure of pitchered and insectivorous plants. At an early
stage in my investigations, I was struck by the perfect blendings in cer-
tain well-known hybrids of the appearance presented by their parents,
and this, not merely in habit, consistence, shape and color, but even in
such minute details as the relative number of stomata in a given area,
the size and shape of the cell hairs, and of the cells from which these
sprung, and the mode of disposition of thickening substance on their
primary cell wall." (p. 543.)

A series of seventeen hybrid Sarracenias formed the first prin-
cipal material. It is stated :

"As one after another of these was passed under the microscope, I was
gradually inclined to believe that a hybrid plant may exhibit blending

264 PLANT HYBRIDIZATION BEFORE MENDEL

of parent peculiarities in every cell. This was easily demonstrated in the
case of epidermal tissues, which are apparently the most plastic of all."
(P- 543-)

Being unwilling to rest upon conclusions derived from such
highly specialized forms, he examined other known hybrids, be-
longing to various orders, including Dianthus hndsayi, Philageria
veitchii^ Saxifraga andrewsiv and churckillii^ and H edy chium sad-
lerianum. "These," he says, "not only verified my previous con-
clusions, but enabled me to extend them in a convincing way."

(P-544-)

It is interesting to note certain characters among those investi-
gated by Macfarlane, in evidence of his conclusions on the inter-
mediacy of hybrids. In the case of Dianthus lindsayi, a cross be-
tween Dianthus harhatus and Dianthus alpinus^ the former par-
ent has 900 stomata on the lower, and 100-400 on the upper
epidermis ; the latter, 600 on the lower, and 460 on the upper
epidermis. The hybrid has 750 stomata on the lower, and 290 on
the upper surface. The epidermal cells of the hybrid were also
found to be intermediate. In the rhizome of the cross between
Hedychium coronarium and H. gardnerianum^ it was found, that
while the starch granules of the former were large, flat, oval
plates, and those of the latter small triangular shells, those of
the hybrid were shaped as though half of the granule in H.
coronarium had been gradually fused with a reduced one of H.
gardnerianum. Investigations of the starch grains in H. coronar-
ium and H. elatum gave similar results. In the orchid-hybrid
known as Masdevallia chelsoni, compared with one of its parents,
some investigations were made on the inheritance of flower color.
This hybrid has purplish-red sepals, the color effect being the com-
bined result of large yellow chromoplasts in the epidermal cells,
and epidermal hairs filled with purple pigment. In M. chelsoni
the size of the chromoplasts was found to be from one-third to
one-half the size of those found in the parent examined. In
Bryanthus erectus^ a bigeneric hybrid of the Ericaceae (a cross
between Rhododendron chamaecistus and Menziesia empetriformis
var. Drummondii)^ in the relative size of the pith cells; in the
structure of the phloem ; in the shape and disposition of the leaf
cells in transverse section; and in the structure of the floral parts,
the hybrid was found to be intermediate between the parents.

PLANT HYBRIDIZATION BEFORE MENDEL 265

In Erica watsorii, a natural hybrid between E. ciliaris and
E. tetralix, the hybrid was found to be very evenly balanced.
Details are given of the anthers only. (p. 544.) In a cross between
Rhododendron ciliatum and R. edgeworthii, the hybrid is said
greatly to resemble the former parent, and scarcely at all the
latter in its gross morphology. In the histological details of leaf
structure, however, "the minute features of both parents were,
strongly traceable in the hybrid." (p. 544.)

In a cross between Cyprvpedium insigne and C. villosum, the
number of the stomata was found to be as follows, for the mag-
nification used :

C. insigne

11-12

C. villosum

21-23

Hybrid

16-17

In a cross between Cypripedium harhatum and C. insigne^ the

relationship was as follows, in respect to the distribution of the

stomata :

C. barbatum 3-4

C. insigne 11 -12

C. ashburtonae (hybrid) 6-7 (p, 544.)

In a rather brief contribution to the Gardeners' Chronicle for
June 20, 1891 (6c), the matter of color, flowering period, and
constitutional vigor of hybrids is discussed. The article in ques-
tion seems to have been contributed in view of Henslow's paper
before the Royal Horticultural Society, May 12, 1891, and re-
viewed in the Gardeners' Chronicle for May 16, on color inheri-
tance in "greenhouse Rhododendrons." Macfarlane holds that the
evidence from Henslow's examination, to the effect that color-
inheritance was more or less a variable matter, should probably
be modified. His statement is interesting, in that it shows an ap-
proach of mind toward a stricter scientific use of the materials in
crossing. He remarks :

"l feel that it will eventually be possible, in the great majority of
cases, to predict the exact color which the hybrid will show, especially
if the color in each parent be due to the presence of one' pigment only"
(6c) ; the examples chosen by Henslow being complicated by the frequent
presence of two pigments, a dissolved red and a granular yellow, in at
least one of the parents.

"if we compare parents which each develop one pigment, or one of
which only is white, i.e., devoid of colour, it may be laid down as a
broad general rule, that the hybrid will be intermediate between the
two, having regard to the size of the floral parts of each."

266 PLANT HYBRIDIZATION BEFORE MENDEL

Macfarlane then cites four cases of Rhododendron crosses which
are color-intermediates between their parents, as follows :

Rhododendron atrovirens purple-crimson

ciliatum pink-white

praecox (hybrid) intermediate

arboreum scarlet

caucasicum white

nobleanum (hybrid) cerise

" ciliatum pink-white

" glaucum dull-pink

" grievei (hybrid) pale whitish-pink

chamaecistus pale pink
Menziesia empetriformis, var. drummondii rose-pink

Bryanthus erectus (hybrid) intermediate

This intermediacy of flower color in hybrids Macfarlane con-
sidered to be best exemplified by cases where yellow is involved,
due to the presence of yellow chromoplasts in the cells. The case
of hybrid Oxlips, crosses between Primrose and Cowslip, are
cited, as also cases of hybrid Hedychiums (fam. Zingiberaceae),
as follows :

Hedychium gardnerianum orange

X Hedychium coronarium white

gave Hedychium, sadlerianum (hybrid) intermediate

and
Hedychium sadlerianum
X Hedychium coronarium
gave Hedychium lindsayi pale, maize-white in bud, be-

coming white in blossom

In cases where yellow, red or blue occur in the same or neigh-
boring cells of a tissue, "the hybrid product may take after one
or the other of the parents in an apparently arbitrary way." As to
a possible theoretical explanation, Macfarlane says:

"Suffice it to say that I regard many of the unequal blendings in hybrid
colour and structure to be due to incompatibility in chemical or mole-
cular union, and the resulting predominance of that colour which is the
more stable or readily evolved of the two." (6c.)

A brief note is given upon inheritance of time of flowering.

From the time of flowering of numerous species, and of hybrids,

at the Edinburgh Botanic Garden, including a record since 1889,

of 800 plants in the rock garden, including also several hybrids

and their parents, it is concluded that:

"These, supplemented by limited observations of my own, all point
distinctly to a flowering period in hybrids closely intermediate between
the parents." (6c.)

PLANT HYBRIDIZATION BEFORE MENDEL 267

On the matter of the constitutional vigor of hybrids, the case
is cited of Monthretia crocosmaeflora, a hybrid between Mont-
hretia pottsii and Tritonia aurea.^

During the winter of 1890-91 the corms of M. pottsii were
scarcely injured; those of Tritonia aurea only survived where
planted against the outer side of a hothouse. The corms of the
hybrid survived to the extent of 60 per cent.

In 1892, Macfarlane published the final results of his studies
on the microscopic structure of hybrids, in the Transactions of
the Royal Society of Edinburgh. (6e.)

This memoir was published as the conclusion of a series of
studies of the microscopic structure of upwards of sixty hybrids,
in comparison with that of their parents. The details are given
with respect to nine hybrids and their parents, as follows :

Philageria veitchii {Lapageria rosea X Philesia buxifolia) (species from
southern Chile)

Dianthus grievei (D. alpinus X D. harhatus)

Geum intermedium (G. rivale X G. urbanum)

Ribes culverwellii (R. grossularia X R- nigrum^

Saxifraga andrewsii (S. aizoon X 5. geum)

Erica watsoni (E. ciliaris X E. tetralix)

Bryanthus erectus (Menziesia empetriformis, var. drummondii X Rhodo-
dendron Chamaecistus)

Masdevallia chelsoni (M. amabilis X M. veitckiana)

Cypripedium leeanum {C. insigne X C. spicerianum)

In addition, he says, "about sixty-five hybrids and their
parents have been examined in some of their parts," to which
partial reference is made as to special particulars. An elaborate
study is also given of the well-known graft-hybrid Cytisus adami^
the accidental result of a case of the budding of Cytisus pur-
pureus upon the stock of Cytisus laburnum {^Laburnum vulgar e)^
a type for which no equivalent sexual hybrid exists, all attempts
to cross the two species sexually having failed. Cytisus purpureus
is a low, creeping, and C. laburnurrk an upright shrub. C. pur-
pureus grows, when grafted upon C. laburnum^ as well as, or
better than upon its own roots. Thousands of grafted plants give
only normal, upright-growing forms of purpureus. In M. Adam's

1 Montbretia is a synonym of Tritonia, a group of thirty South African
bulbous plants of the Iridaceae, belonging to the Gl«dioleae, of the
sub.-fam. Ixiodeae.

268 PLANT HYBRIDIZATION BEFORE MENDEL

particular case, originating in 1829, the shoot arising from the
bud was manifestly a vegetative hybrid in its characters, and has
since been multiplied, and introduced into botanical gardens and
elsewhere. For a long time, until the experiments of H. Winkler
(1907-10) on "graft-hybrids" (chimaeras), Cytisus adami was
almost the sole type-representative of the class. Macfarlane de-
votes eleven pages to the discussion of the anatomical details of
the plant and its stock-scion parentage.

No summary of the whole of Macfarlane's investigation can
be given, except to state that in general the hybrid forms studied
gave almost complete intermediacy in most of the principal de-
tails of structure. The case of Philagena veitchii, produced in
the nurseries of Messrs. Veitch at Exeter, was first described fully
in its gross morphological characters by Dr. M. T. Masters in
the Gardeners' Chronicle for 1872. The two parents differ widely
in habit, Lapageria rosea being a twining plant, 25 to 30 ft. in
length, inhabiting the forests along the lower levels of the Andes,
from Valdivia to Concepcion ; Philesia buxifolia being a "low-
growing, dense, tufted shrub, attaining a height of ten to fifteen
inches," inhabiting "the swampy, unproductive wind and rain-
swept region extending from Chile southwards to Tierra del
Fuego." The hybrid, which is called a "scrambling shrub," is
described by Masters as being in habit more nearly akin to the
female parent {Lapageria) ; the foliage intermediate, but nearest
like Philesia; flower stalk, calyx and corolla more like Philesia;
stamens and pistil resembling more the Lapageria parent.

The anatomical characters of the hybrid and of its parents may
be briefly summarized from Macfarlane's details as follows: (Di-
ameters in jx.)

LAPAGERIA PHILESIA PHILAGERIA (f^ HYBRId)

Outer cortex cells

60 20 32-35

Inner cortex cells (av.)
100-120 45-50 70-75

Bundle-sheath cells
48-50 (radially) 35 (radially)

35-40 (tangentially) 18-20 (isodiametric) 20-22 (tangentially)

Cells of stem
Epidermal cells
100x30x25 80x30x35 60x30x40

PLANT HYBRIDIZATION BEFORE MENDEL

269

Vascular bundle cells

Xylem

180-200

250
Phloem {sieve-tubes)

400

20-25

25-28
Phloem {companion cells)

40-45

5-8

2 layers

110x30 (upper)

75x35 (lower)

7-9

Cells of leaf palisade layer
2-3 layers
70—80x35 (upper)
50 — 60x35 (second)
Median vascular bundle of petiole

8-10

3-4 layers
35x35

37-40

30-32

The structural details of cells from Cytisus adami and its
stock-graft parents are as follows :

CYTISUS LABURNUM CYTISUS ADAMI (gRAFT-

(stock) hybrid)

Cortex
13-15 layers 13-15 layers

sclerenchyma cells, sclerenchyma cells, none 5 longitudinal masses
none

Leaf
epidermis covered with epidermis, glabrous
spindle-shaped hairs

Vascular bundle of petiole
Phloem (sieve-tubes)
6 4-4.5

Xylem (tracheids)
20 14-15

Epiderm.is
(stomata in field)
(X400)
0 (upper) 12-14 (upper)

40 (lower) 17-20 (lower)

Flower,
Petals.

Standard.
glabrous marginal fringe of 60-65

hairs
wings
glabrous marginal fringe of (av.)

90 hairs
Keel
glabrous marginal fringe of

48-50 hairs
Stamens
Pollen-cells (diam.)
2 1 -23 M 23-25 i" 25-26 At

cytisus purpureus
(scion)

7-10 thin-walled layers
5 longitudinal masses
of sclerenchyma cells

epidermis, glabrous

3-4
8

27-30 (upper)
30 (lower)

marginal fringe of
125-130 hairs

marginal fringe of
160-170 hairs

marginal fringe of
100-1 10 hairs

270 PLANT HYBRIDIZATION BEFORE MENDEL

Further details from Macfarlane's rather exhaustive anatom-
ical studies cannot be given, but the above will suffice to show
the manner of the investigations, and the general type of the
results.

Some general conclusions which Macfarlane derives are inter-
esting. In e.g., the production of epidermal hairs, it is stated:

"if the parents possess one or more kinds that are fundamentally simi-
lar, but which differ in size, number and position, the hybrid reproduces
them in an intermediate way. ... If the hairs of two parents are pretty
dissimilar, instead of a blending of these in one, the hybrid reproduces
each, though reduced in size and number by half." (p. 270 6e.)

"The distribution of stomata over any epidermal area has been proved
to be a mean between the extremes of the parents, if the stomata of
the parents occur over one surface or both, and if the leaves are similar
in consistence, but ... if the stomatic distribution and leaf consistence
differ in the parents, this may give rise to correspondingly different re-
sults in the hybrid." {ib., p. 271.)

". . . every hybrid has yielded a large series of examples which prove
the size, outline, amount of thickening, and localization and growth of
cell walls, is, as a rule, intermediate between those of the parents."
{ib., p. 271.)

Interesting is the account of the laying down of secondary
cell-wall thickenings, which, whether of a cuticularized, lignified,
or colloid nature, in the hybrid constitute a mean in amount and
mode of deposition between the extremes of the two parents. The
most striking illustration is that of the bundle-sheath cells of
Philageria and its parents, where 5 lignified cell-lamellae are
found in Lapageria, 11-12 in Phtlesia, and 8-9 in Philageria.

In leaves of the same age and like position, the chloroplasts,
in depth of color and size, are found to be intermediate in the
hybrid. (Saxzfraga, ib.^ p. 272.)

As the result of his histological investigations, Macfarlane came
to the conclusion that the male and female elements in the fer-
tilization, act complementarily to a degree amounting to half, for
each of the two sexes, in the fertilization product. The principal
comment is as follows :

"No matter what tissue or set of tissues is chosen, if the cells compos-
ing such are tolerably diverse in the parents, one can trace with ease the
modifying action which both sex elements have had on them, while these
clearly prove that each sex element, after union with its complementary
element, represents potentially half its former individuality, or retains
half its former hereditary properties." {ib., p. 273.)

PLANT HYBRIDIZATION BEFORE MENDEL 271

Macfarlane uses the term "unisexual heredity" to designate the

cases in which

". . . structures found only in one parent, and with no corresponding
counterpart in the other, are handed down, though reduced by half."
{ib., p. 273.)

In this connection he makes a rather interesting comment :

"Now it has been repeatedly noticed that when a species varies from
the normal, it seldom does so in only one point or structural detail, but
a certain variation-wave, so to speak travels through the entire organism,
giving it that combined set of characters which make it rank as a sub-
species." {ib., p. 274.)

As what he terms "bisexual heredity," Macfarlane designates

such cases as Ribes culverzvelhi,

". . . in which the simple hairs of R. grossularia and the oil-secreting
peltate hairs of R. nigrum are both separately reproduced, though about
half as large as those of the parents." (p. 274.)

The case of the similar inheritance of epidermal hairs in Saxi'

fraga and Carduus hybrids is also cited. It is interesting to note

that Macfarlane reports that he knows of no cases

". . . where internal elements or tissue-masses are thus separately re-
produced" (p. 274), and he further notes that "all the hybrids in which
the above has been observed are derived from parents considerably re-
moved in systematic relationship, and the incompatibility of blending the
diverse types of hairs probably explains their appearance as separate
growths." (ib., p. 274.)

He says further :

"But the general principle here illustrated on an exaggerated scale is
that the offspring of two parents may inherit from each diverse peculiari-
ties which, instead of blending evenly, retain their separate individuality.
Future experiment and observation alone will decide for us whether
these can be passed down through two, three, or more generations, and
till we have the evidence it would be impossible to generalize." {ib.,
p. 274-)

A theoretical attempt at the resolution of the behavior of the

characters in a hybrid into their factorial components is further

enunciated :

"if we view a fertilized egg of any plant, which is about to segment to
form an embryo, as being not merely a chemically complex nucleated
mass of protoplasm, but as a microcosm in which the orderly-arranged
molecules of the conjugated male elements have so exactly fitted into
and become united with corresponding molecules of the female element,
that after conjugation, coordinated groups of molecules are set apart as
stem-producers, root-producers, leaf-producers, and hair-producers, we
will have done much to clear away obstacles. But physically there is

272 PLANT HYBRIDIZATION BEFORE MENDEL

no reason why we may not assume that each cell of the future plant has
representative molecules in the apparently simple egg." {ib., p. 276.)

The general matter of fertility or sterility in the case of crosses
is briefly epitomized in the following statement:

"To sum up present-day experiences, it may be said that crosses be-
tween species that are nearly related in structure and habit can readily
be effected, and the offspring may be largely fertile, at least among cer-
tain genera. Crosses between species that differ considerably in form,
flower color, and habit, are more difficult to perform, and the hybrids
are largely sterile, while crosses between such divergent species or
genera as Dianthus alpinus and barhatus, Saxifraga geum and Aizoon,
Lapageria and Philesia are almost wholly sterile." {ib., p. 277.)

And again :

"if we return now to hybrid production of the more extreme types,
though in virtue of the attraction which exists between sexual elements,
the original male and female cells from parents of different species —
in the absence of cells from the same species — may be capable of uniting,
and, in the process, of overcoming the repulsion due to dissimilar co-
relative molecules in each, when the attempt is made by all the herma-
phrodite cells of the resulting hybrid organism to concentrate repre-
sentative hermaphrodite groups of molecules, many cases will occur in
which these will blend imperfectly, owing to difference in the composi-
tion and amount of chemical substances present, or interference and can-
celling effects due to unequal propagation pf waves of motion between
the molecules. Thus many groups of molecules will break down or fail
to reach their destination, so that gaps or vacancies will occur in the
organic completeness of the pollen or egg cell. It will then have the
shrivelled half-empty look so characteristic of hybrid sex-cells that are
sterile. In hybrids from more nearly related species the interfering or
cancelling effects will be reduced in proportion, and a larger number of
sex cells will have a chance to mature." {ib., p. 281.)

The last paper of Macfarlane's dealing with the histological
details of plant hybrids, is entitled "Observations on some hy-
brids between Drosera filiformis and D. intermedia,'' published in
1899. (6g.)

The investigation was conducted upon a natural hybrid between
the above species, discovered near Atco, New Jersey. A group of
eleven plants was found, intermediate in form and color between
the two above local species. These were removed to the green-
houses of the Botanical Garden of the University of Pennsyl-
vania, where a histological examination was made of the two
parent species and of the hybrid. The comment is made that

"The phenomenon which the writer terms 'bisexual heredity' receives
several striking exemplifications. Where two more or less diverse growths
have occurred, one on either parent, these have been shown to be re-

PLANT HYBRIDIZATION BEFORE MENDEL

273

produced, not in blended fashion, but as distinct structures reduced
either in size or number or both." (p. 98.)

Following are the details of measurements in the parents and
the first generation hybrid, for the principal characters studied.

Tissue
Leaves

Presence of
stomata

D. filiformis D. intermedia

8 in. long; 1/2 Av. 1 1/2 in.
in. wide. Petiole, long. Blade 1/5

3/8 in.-5 in.
long, non-gland-
ular

in. wide, sharp
difference be-
tween petiole
and lamina.
Base of the peti-
ole has a quad-
rangular area
also

Upper epidermal Upper epidermal
cells of this cells of this

area average area, 225x28/",

250x38/^. Chlo- and contain a
roplasts few, very few small

scattered and chloroplasts

small ; each 2.5
to 3/" diam.
Stomata not
present on this
area

Lower epidermis Lower epidermis
of this area has has elongated

Hybrid

Typical summer
leaves may be
10-11 in. and
greatly attenu-
ated at tips, but
average 3 1/2
in., of which 1/2
in. may be peti-
ole. No basal
quadrangular
area; intermedi-
ate in size and
shape

Upper epidermal
cells, 188-
200x32/". Chloro-
plasts small and
few

cells longer and
narrower,
185x20/", well
filled with large
chloroplasts,
each 7.5-8/"
across

narrow cells,
200-225x15/"

Lower epidermal
cells average
186-195x21/"
and chloroplasts
measure 2.5/"

A few stomata,
each 40x23-25/".
2-celled sessile
glands of stoma-
like character

No stomata, and
instead of the
2-celled glands,
there are gland-
ular bifid hairs

Numerous
2-celled glands,
and also bifid
hairs, but of re-
duced size

2-celled gland-
ular hairs

28x18/", slightly
elevated above
surface

45-50At high X 37/^
across

33/i high X 32/t
across

274

PLANT HYBRIDIZATION BEFORE MENDEL

Sto7nata {lower 361" long x 24M 26x25/*
surface) wide

32/* diam.

Chloroplasts
of guard cells

20-22, and meas-
ure 2/* diam.

12-14, and meas- 15-17, and meas-
ure 1.8/A diam. ure 2.5/^ diam.

Tentacles

Pigment confined Pigment richest Pigment less

to the oval or
elliptical head
of each tentacle,
Hair-stalk green

in the head-cells,
but distributed
in the cells of
each stalk for
2/3 its length

pronounced, and
extends 1/3 to
nearly 1/2 the
length of the
stalk

Head of ten-
tacle

22x1 65M

220X 1 05M

21OX125M

Stomata of
lamina {upper
epidermis)

40x30/ii ; 9 in an
area. 300M across

27X22M; 7 in an
area. 3CX)M across

34x25/* ; 8 in an
area. 300/* across

Axis of
inflorescence

9 3/4 in.

5 1/2 in.

6 3/4 in.

Cortex

4-5 rows of thin- 1-2 layers of 2-3 layers of

walled parenchy- parenchyma. 3-4 parenchyma cells.

ma cells, with
abundant chloro-
plasts. 5-6 layers
of sclerenchyma
tissue

layers of slightly 4-5 layers of
sclerench^'ma sclerenchyma

tissue tissue

No. of flowers
in inflorescence

Size of flowers

7/8 in. across ;
purple and pink

1/4 in. across;
pure white

3/8 in, across ;
faintly pink

Pollen grains

56/* diam.

44/* diam.

48-50/* diam.

Macfarlane deserves to be remembered, therefore, among those
who have contributed to build up a substantial knowledge of the
hybridization process, because of the exact character of his in-
vestigations, and his anticipation of the discoveries made only
after the publication of Mendel's papers. His contribution, funda-
mentally speaking, may be summed up in his own words as
follows :

"From extended observations that the writer has made, alike on living
plants, and on their minute tissues, he adheres to the view that an aver-
age hybrid is nearly intermediate between the parents." (6f .) And that :

"Every cell of a plant inherits the peculiarities of both parents, at
times in a perfectly balanced way, so far as our limited powers of study
can carry us, at times with an evident leaning or bias to one parent." (6a.)

PLANT HYBRIDIZATION BEFORE MENDEL 275

c. Wilson.

In a paper entitled "The structure of certain new hybrids
(Passiflora, Albzica, Ribes^ Begonia^ etc.),'' John H. Wilson re-
ported, to the meeting of the Hybrid Conference in London in
1899, the following data regarding the structural character of
hybrids in species of the above genera. Inasmuch as this consti-
tutes another one of the few pre-Mendelian attempts at the meas-
urement of the characters involved in hybridization, the results
are given in some of the principal cases, as follows :

Branches

Passiflora buonapartea X -P- coerulea

9 Stout, tetrago- $ Almost cylin-
nal-winged. light drical ; 5-6 well
green defined angles ;

glaucous-green
with reddish
purple

F, hybrid.
Stouter than the
9 and more angu-
lar; about 5 an-
gles. Much pur-
ple coloration.

Leaf-blades

Large, ovate-
cordate, some-
what acuminate :
dorsal, dark
green; ventral,
lighter green ;
8 5/8 in. long ;
7 1/4 in. broad ;
entire

5-, often 7-lobed, Invariably 3
by branching of lobed, 7 1/2 in
the two lower
lobes ; occasion-
ally 3-lobed ; dor-
sal, deep green ;
ventral, glaucous.
Minute marginal
glands at leaf
notches, near
base of lobes ;
5 in. long; 7 3/8
in. broad

long, 10 3/4 in.
wide at tips of
lobes. Average
length, 5 1/4 in.
X 7 1/2 in.

Leaf

Passiflora alba X P- buonapartea

Long-ovate, cor-
date, somewhat
acuminate ; en-
tire. 8 5/8 in.
long, 7 1/4 in.
wide

Lamina, 3-lobed.
6 in. long, 6 1/2
in. wide. Petiole
3 1/4 in. or
more

3-lobed, 6 in.
long, 7 in. wide

No. of flowers
in inflorescence

Ribes nigrum X R. grolsularia
7-8-13 1-2

Av. 3

Ovarian glands

Sessile, O.15-O.17
mm. diam.

0.1 mm. diam.;
stalks 1.2 mm.
long

0.1-0.13 mm.
diam., length of
stalk. 0.03-0.13
mm.

276 PLANT HYBRIDIZATION BEFORE MENDEL

d. Darbishire.

Darbishire, in 1908 (1), appears to have been the first, since
the re-discovery of Mendel's papers, to demonstrate further the
facts brought out by Macfarlane's earliest investigations. Dar-
blshire's experiments involved the crossing of a variety of peas
in which the cotyledons were green and round (Eclipse), with
one in which the cotyledons were yellow and wrinkled (British
Queen). In the (F^), out of 579 starch grains in the cells of the
cotyledons, 356 were single and 223 compound. The singles were
more nearly round than in the Eclipse parent, the single starch
grains (av. of 102 grains), as compared with an index of 66:14
in the length-breadth index, being 92 : 19 in the Eclipse parent
(av. of 232 grains). In the compound grains, the commonest
types were those with 4, 5, or 6 component parts (7 and 8 being
rarer), 2 and 3 being intermediate in frequency between those
with 4, and 5 and 6 on the one hand, and 7 and 8 on the other.
Grains with 7 and 8 component parts were not much larger than
those with 4, 5, and 6, while grains with 2 or 3 were always
found to be conspicuously smaller than those with 4, 5, and 6.
In the British Queen parent, the grains (all compound, an occa-
sional one only entire), have 2-8 component parts.

32. Spillman. Mendelian Results with Wheat, prior to 1900.

In 1901 appeared a brief but interesting and somewhat note-
worthy paper on inheritance of characters in wheat hybrids, by
W. J. Spillman, then of the Washington State Experiment Sta-
tion, now of the United States Department of Agriculture. The
paper, read before the Fifteenth Annual Convention of the Asso-
ciation of American Agricultural Colleges and Experiment Sta-
tions, November 12-14, 1901, represented a definite effort to ob-
tain results of a quantitative character. The results, so far as
they were attained, are stated in somewhat Mendelian fashion,
although a knowledge of the then just published reports of Men-
del's investigations had not yet reached the author. Nageli, Sachs,
and Darwin are quoted.

The study was based upon an undertaking to obtain a winter
wheat for Eastern Washington. Some 15*0 varieties were tried,
but none were found satisfactory, the worst common defects being
shattering of the grain, lodging, susceptibility to smut (bunt).

PLANT HYBRIDIZATION BEFORE MENDEL 277

and unsatisfactory milling qualities. Having failed to find suit-
able varieties, it was undertaken to produce them by crossing the
most promising winter varieties with the leading spring varieties
known to be locally adapted.

Beginning with 1899, 14 crosses were made between parents of
spring "Club" wheat {Triticum compacturn)^ and the ordinary
vulgar e types of winter wheat. From these crosses 215 plants
were harvested in 1900. Of these, 149 proved to be hybrids, being
intermediate in type between the parents. The remainder were
identical with the female parent, thus showing that the flowers
had been self-fertilized. The following remarkable statement oc-
curs :

"No important variations occurred in the first generation, except as
noted below, but when the heads appeared on the second generation,
a remarkable state of affairs was seen to exist. At first glance it appeared
that each of the hybrids had split up into all sorts of types, but closer
inspection showed that in every case but one, which is noticed later, the
forms in each plot were simply combinations of the characters of the
parent forms. Further inspection revealed the fact that, in plots of
similar breeding, exactly the same types were present. This suggested
the idea that perhaps a hybrid tended to produce certain definite types,
and possibly in definite proportions." (p. 88.)

All of the hybrid plots were accordingly assorted into types,
and the proportions of each type determined. The results con-
firmed the idea that definite types and proportions existed in the
progeny. The statement follows :

"if similar results are shown to follow the crossing of other groups
of wheat, it seems entirely possible to predict, in the main, what types
will result from crossing any two established varieties, and approximately
the proportion of each type that will appear in the second generation."
(p. 88.)

The statement is then made :

"with the exception already referred to, the second generation con-
sisted of the two parent types, and of all the intermediate types possible
between them." (p. 88.)

The instance is given where one parent had long, bearded
heads, and the other short, beardless heads ; six types could be
distinguished :

"... 2 of these had long heads like one of the parents, 2 others short
heads like the other parent, and 2 were intermediate ; and one of each
of these 3 groups had beards, while the other had none." (p. 88.)

278 PLANT HYBRIDIZATION BEFORE MENDEL

In crosses involving pubescent chaff but no beards, a similar
set of 6 types appeared. Where one of the parents had pubescent
chaff of dark brown color, 12 types were theoretically possible
and were actually found. The remark follows :

"it was stated above that the first generation tends to be the same in
similarly bred hybrids and is intermediate between the parents." (p. 89.)

This was found to be the case in 1 1 out of 14 crosses. In a
case involving "velvet" (pubescent) chaff, there were 12 types
in the second generation, 6 with velvet, and 6 without. In the
first generation, 1 out of 9 plants differed from the rest only
in having no "velvet" or pubescence on the chaff. Such plants
of the first generation produced only the 6 types without "velvet"
in the second generation.

A general statement, also quite remarkable in character, is made
to the effect that :

"It has been stated by nearly all investigators that there is a tendency
in the second and later generations, to revert to the parent form. It
seems possible that there is a more accurate way of stating this. The
types that tend to occur in the second generation, as indicated by our
results, include all possible combinations of the characters of the two
parents. This of course ijicludes the parent forms themselves, and we find
the parent forms repeated in the second generation, constituting appar-
ently certain definite portions of this generation!' (Italics inserted.)
(p. 89.)

Another interesting statement then follows :

"Another important fact, that is clearly revealed by the tables of
percentages, is that the type that is most abundant in the second genera-
tion is the same as the first generation type, whether the latter is of the
usual intermediate type or otherwise. The exceptions to this are so rare
as to render them doubtful." (Italics inserted.) (p. 89.)

So far as the writer knows, this constitutes the first and, in-
deed, the sole observation from the time of Kolreuter, with the
exception of Mendel's own investigation, to take note of the fact
that, in the second generation, the most abundant type to appear
is the type of the first generation itself. This is an observation
of the fact which Mendel definitely worked out, of the appearance
in the second generation of 2 Dr to one each of the DD and rr
types, the Dr type being the reappearance of the original Dr
combination of the first generation.

Spillman goes on to comment upon the work of hybridization
done since the time of Kolreuter, having special reference to the

PLANT HYBRIDIZATION BEFORE MENDEL 279

work of the various breeders of the cereals, Garton Brothers,
Rimpau, Farrer, Vilmorin, and others. The statement follows :

"Sachs remarks that Kolreuter, the first man to produce plant hybrids,
covered the ground so completely that subsequent investigators have
added little to his results."

The comment is then made :

"But quantitative investigations have been too seldom undertaken. It
seems to me that they are not unimportant." (p. 93.)

The quantitative results in question follow in very accurately
arranged detail, in 14 tables, covering the quantitative distribu-
tion of the types of the second generation. The characters of
the heads involved are, long and short, bearded and beardless ;
velvet (pubescent) chaff, and glabrous chaff ; brown-colored and
light-colored chaff. The investigator had no conception at the
outset, as had Mendel, of consciously crossing contrasting charac-
ter-pairs as such, and unfortunately did not take note of the
fact of dominance in the case of the bearded-beardless, and
pubescent-glabrous crosses. This was unquestionably due to the
fact that length of head, the most salient character, did not show
Fj dominance for long X short crosses, but intermediacy.

In all the tables, the numbers which reproduce the characters
of the first generation are printed in heavy type, so that there is
statistical evidence of the dominance of characters involved, al-
though no reference is made to it as such.

The individual columns give, in exactness and detail, the dis-
tribution of the plants in classes, according to the head-characters,
but there is no summary of the proportionate numbers of these
types. With the total available data obtained, it would have been
possible for Spillman to have not only verified F^ dominance for
beardlessness over beardedness, pubescent chaff over glabrous
chaff, and brown pubescence over light pubescence, but also to
have determined the ratios of the distribution of those characters
in the second generation. A few of the numerical results follow,
summarized from some of the tables.

The data comprising Spillman's results are given in fourteen tables
(pp. 94-98 of the memoir). The principal data from these tables which
may be taken as examples of his Mendelian ratios, are those dealing
with the inheritance of length of spike, awns, pubescence of the glumes,
and color of glumes. In all of the tables, the progeny are classified in
percentages, first, as to long, semi-long and short (head-length charac-

Inter-vulgare Crosses

Red Chaff $

X White Track $

Red Chaff $

X Mcpherson $

Red Chaff 9

X Jones' Winter Fife $

Red Chaff 9

X Farquhar $

280 PLANT HYBRIDIZATION BEFORE MENDEL

ter) ; as to pubescent and glabrous chaff, beardless and bearded heads,
brown and light-colored glumes. The varieties used in the crosses are
as follows ;

Compactum-vulgare Crosses Table

Little club {compactum) $ X Emporium {vulgare) $ I

Little club {compactum) 9 X Jones' Winter Fife {vulgare) i II

White Track {vulgare) 9 X Little Club {compactum) 6 III

Little Club {compactum) 9 X Valley {vulgare) $ IV

Emporium {vulgare) 9 X Little Club {compactum) $ IX

Little club {compactum) 9 X Farquhar {vulgare) ^ XI

Farquhar {vulgare) 9 X Little Club {compactum) $, XII

Valley {vulgare) 9 X Little Club {compactum) ^ XIII

Little club {compactum) 9 X Turkey {vulgare) ^ XIV

VI
VII
VIII
Red Chaff 9 X Lehigh ^ X

Summarizing the results in the tables for Spillman's fourteen crosses,
the data of F^ inheritance for the characters investigated are as follows :

Compactum-vulgare Crosses Table

Long 2546.1

Semi-long 37544

Short 1967.1

A ratio of 1 : f 1.4I : 1, or approximately 1 : 2 : 1.

Awns

Heads awnless 4770-3

Heads awned 880.8

A ratio of 5.4 : l, instead of the expected one of 3 : 1. However, if
individual tables are taken (omitting Table XII) normal ratios exist.

Pubescence of Glumes

Glumes pubescent 4224.7

Glumes glabrous 137 ••8

A ratio of 3.1 : 1

Color of Glu7nes

Glumes brown in color 3143.7
Glumes light 1061.8

A ratio of 2.9 : 1
Referring to the results from individual tables, the following may be
cited in illustration, from the compactum-vulgare crosses:

PLANT HYBRIDIZATION BEFORE MENDEL 281

A Awnless-awned {glumes)

Table XIII (Valley ? X Little Club $ )

Awnless Atoned Ratio

Types I and II (heads long) 197.O 68.8 2.8 : 1

Types III and IV (heads intermediate) 405.9 136.6 2.9 : 1

Types V and VI (heads short) 219.8 72.1 3 : 1

Table XIV (Little Club $ X Turkey $ )

Awnless Awned Ratio

Types I and II (heads long) 130.5 44.O 2.9 : l

Types III and IV (heads intermediate) 222.O 125.9 1.7 : l

Types V and VI (heads short) 120.6 46.O 2.6 : l

Table IX (Emporium $ X Little Club $)

Awnless Awned Ratio

434.1 145.1 2.9 : 1

B Pubescent-glabrous {glumes)

Table II (Little Club $ X Jones' V^inter Fife $ )

Pubescent Glabrous Ratio

Types I and II (heads long) 444-1 U8.4 2.9 : l

Types III and IV (heads intermediate) 769.4 274.2 2.8

Types V and VI (heads short) 409.8 155.5 2.6

Table XII (Farquhar $ X Little Club $ )

Pubescent Glabrous Ratio
Types V and VI (heads long, glumes brown) 582.3 149.7 3.8 : l
Types VII and VIII (heads long, glumes light) 206.3 324-0 no ratio
Types IX and X (heads intermediate, glumes

brown) ^ 700.2 . 165.] 4.2 : 1

Types XI & XII (heads intermediate, glumes

light) 185.5 54-3 3-4 : 1

Types XIII and XIV (heads short, glumes

brown) 243.7 92.9 2.6 : l

Types XV and XVI (heads short; glumes light) 160.8 17.4 5 : l

It thus appears that Mendelian results for length of head (in
compactum-vulgare crosses), inheritance of awns, pubescence of
glumes and color of glumes were reported in. November, 1901, in
complete statistical form, although not analyzed with reference to
the ratios.

Exact data do not seem to be obtainable as to inheritance of
length of spike in compactum-vulgare crosses, but in crosses be-
tween spelta and compactum (Malinowski, 1921), the length of
heads and the structure of the spikelets were reported as being
controlled each by a single gene. The Fo is reported as splitting

282 PLANT HYBRIDIZATION BEFORE MENDEL

according to the ratio 1:2:1 {Triticum spelta, vulgar e and
compactum all have 42 chromosomes as the diploid number).

Dicoccum-vulgare crosses by the same investigator gave likewise
a 1 : 2 : 1 ratio for inheritance of length of spike, dicoccum hav-
ing 28 chromosomes as the diploid number.

The fact that results for awn-inheritance are, Fj^ awnless ; F2
awnless-awned, 3 : 1, was first determined by Biffen (1905), and
has since been repeatedly confirmed by the work of some fourteen
investigators.

The dominance of pubescence over glabrousness in the glumes
was also first determined by Biffen in 1905, in vulgar e crosses.
Results for similar inheritance in other Triticum crosses has like-
wise been determined. Exact investigations in inheritance of brown
glume color were first carried out by Nilsson-Ehle in 1909, the
Fo ratio being found for the most part to be 3 : 1 but sometimes
15 : 1. Similarly Love and Craig (1919) found a 15 : 1 ratio
between a brown vulgare and a yellow durum^ thus indicating the
presence of two genes for brown glume color.

This will suffice for a brief review of the present genetic status
of the characters investigated by Spillman.

The writer concludes, as a result of his investigation :

"while the results here reported are not sufficient to justify the posi-
tive assertion that certain quantitative laws govern the transmission of
parental characters to hybrid offspring, yet they point so strongly in this
direction, that we may state some of these laws provisionally, looking to
future investigation for their confirmation, modification, or rejection."
(P- 93-)

These provisional laws are stated as follows :

"That similarly bred hybrids tend to be alike in the first generation,
and to be intermediate between the parent forms, and that rarely an in-
dividual resembles one parent more or less closely, has been stated by
others. We may add to this, provisionally at least, the following :

.(1) "In the second generation of hybrids of similar breeding (with
close fertilization), the same types tend to occur and in definite propor-
tions ; 2 of these types are like the parents, the others include all possible
intermediate forms.

(2) "with few exceptions, the most abundant type in the second gen-
eration is the same as the type found in the first generation, whether the
first generation was strictly intermediate between the parents or not."
(P- 93-)

It is a matter of some interest to record such a succinct and
definitely scientific attempt at a statement of the conditions gov-

PLANT HYBRIDIZATION BEFORE MENDEL 283

erning the second generation of hybrids, based on the results of

a carefully planned experiment, considerable in extent, and with

the data definitely classified in a statistical, and to that extent a

quantitative manner.

A rather interesting statement of a more or less Mendelian type

is made in the concluding portion of the paper.

"We have begun investigations with a view to ascertaining whether
these quantitative laws extend to hybrids between other groups of wheat
varieties, and whether, when a composite is formed from several varie-
ties, all the types will appear that could be formed by combination of
parent characters. It is interesting to note the possibilities that are open
to the breeder should this prove to be the case. We could then produce
anything we desire if we can find varieties possessing the characters we
wish to combine." (p. 94.)

The concluding statement is :

"In work of this character, the larger the number of individuals, the
greater the probability of finding any desired combination of characters.
It is therefore desirable to secure as many grains of each cross as pos-
sible, and to raise all their progeny. Those who are familiar with the
details of such work, will realize that this entails an enormous amount
of labor, and one can hardly hope for success without both patience and
enthusiasm, coupled with some training." (p. 94.)

This concludes the discussion of a paper that has been perhaps
considerably overlooked, but which represents a very definite at-
tempt to analyze the data of heredity upon a rational and indeed
almost a Mendelian basis.

This closes the survey of the work of the students of hybrid-
ization, from the date of the appearance of Mendel's papers in
1865 until their reappearance to the scientific world in 1900.
This period, while important for the imposing names of Darwin
and Galton, was also important for the propounding of the law
of the disjunction of hybrids by Naudin, which, as we have seen,
led Darwin to theoretical conclusions regarding the behavior of
the characters in the sexual cells in the case of hybrids, similar in
general character to the conclusion which Mendel's investigation
established.

To the modern student of breeding, it seems exceedingly
strange that to none of those who carried on the earlier experi-
ments in hybridization it should have occurred to determine,
whether the second or "variable" generation of hybrids was any-
thing other than a disorderly congeries of forms ; whether, beneath
this apparent disorder, there might not be concealed some law.

284 PLANT HYBRIDIZATION BEFORE MENDEL

BIBLIOGRAPHY

1. Darbishire^ A. D.

On the result of crossing round with wrinkled peas, with
especial reference to their starch grains. Proc. Roy. Soc. Sec. B.
80:122-135. No. B537. March 13, 1908, of the Proceedings.
Read November 14, 1907; pub. December 1908.

2. Gallon^ Francis

(a) Natural Inheritance. London, 1889.

(b) The average contribution of each of several ancestors
to the total heritage of the offspring. Proc. Roy. Soc.
61 1401, 1897.

3. Gold Schmidt^ Richard.

Einfiihrung in die Vererbungswissenschaft. 4th ed., Leipzig,
1923-

4. Henslow^ George.

Journal of the Royal Horticultural Society, May 12, 1891.
Reviewed in Gardeners' Chronicle, 3rd. ser. 9:618-20. May
16, 1891.

5. Henslow, J. S.

On the examination of a hybrid Digitalis. Cambridge Philo-
sophical Transactions. 4:257-78, 1833. Read November 14,
1831.

6. Macfarlane^ J. M.

(a) The microscopic structure of hybrids. Gardeners' Chron-
icle, 3rd. ser. 7:543-4. May 3, 1890.

(b) The minute structure of plant hybrids. Nature, 44:119.
June 4, 1891. (A note referring to a paper by Macfar-
lane on the comparison of the minute structure of plant
hybrids with that of their parents. Report of the meeting
of May 4 of the Royal Society of Edinburgh. Statement
to the effect that : "He finds that the minute structure
of the hybrid, like the larger features, is always inter-
mediate in character between the corresponding struc-
tures of the parents.")

PLANT HYBRIDIZATION BEFORE MENDEL 285

hybrids. Gardeners' Chronicle, 3rd. ser. 9:753-4. June
20, 1891.

(d) Anatomical structure of hybrids. Journal of Horticul-
ture, Cottage Gardener, and Home Farmer, 3rd. ser.
23:86. July 30, 1891. Also, report of meeting of June
21 of the Royal Horticultural Society, entitled, "Micro-
scopical structure of hybrids."

(e) A comparison of the minute structure of plant hybrids
with that of their parents, and its bearing on biological
problems. Transactions of the Royal Society of Edin-
burgh, 37; pt. 1, (No. 14) 1892, pp. 203-86, 8 plates.

(f) Hybridization, its benefits and results to ornamental
horticulture. American Florist, 9:81-4, August 31, 1893.
(Brief comment on p. 82 on the intermediacy of hy-
brids.) Gardeners' Chronicle, 3rd. ser. 14:361-2; 395-6,
September 23 and 30, 1893. (Reprint of the article in
the American Florist, above.)

(g) Observations of some hybrids between Drosera filifor-
mis and D. intermedia. University of Pennsylvania Con-
tributions, 2:87-99. 1899.

7. Spillman, W. J.

Quantitative studies on the transmission of parental char-
acters of hybrid offspring. Proc. 15th Ann. Convention of
the Ass'n of American Agricultural Colleges and Experiment
Stations, held at Washington, D.C., November 12-14, 1901.
U.S. Dept. of Agriculture, Office of Experiment Stations,
Bulletin No. 115. pp. 88-98.

8. Wilson^ John H.

The structure of certain new hybrids (Passiflora^ Albuca,
Ribes^ Begonia, etc.) Journal of the Royal Horticultural So-
ciety, 24:146-80, 1900. See also: Report, Hybrid Conference,
London, 1899 ; and Publications of the University of Penn-
sylvania, New Series, No. 5, Contributions from the Botani-
cal Laboratory. Vol. II, No. 1. 1898.

CHAPTER X

33. The Discovery of Gregor Mendel.

f ■~^HE year 1900 marks the beginning of the modern period
in the study of heredity. Despite the fact that there had
been some development of the idea that a living organ-
ism is an aggregation of characters in the form of units of some
description, there had been no attempts to ascertain by experi-
ment, how such supposed units might behave in the offspring
of a cross. In the year above mentioned the papers of Gregor
Mendel came to light (5), being quoted almost simultaneously in
the scientific contributions of three European botanists, De Vries
in Holland (3), Correns in Germany (2), and Von Tschermak in
Austria (6). Of Mendel's two papers, the important one in this
connection, entitled "Experiments in Plant Hybridization," was
read at the meetings of the Natural History Society of Briinn in
Bohemia (Czecho-Slovakia) at the sessions of February 8 and
March 8, 1865. This paper had passed entirely unnoticed by the
scientific circles of Europe, although it appeared in 1866 in the
Transactions of the Society. From its publication until 1900, Men-
del's paper appears to have been completely overlooked, except
for the citations in Focke's "Pflanzenmischlinge," and the single
citation of Hoffmann, elsewhere referred to.

Gregor Johann Mendel, a monk of the Augustinian order in
the Catholic Church, was the son of a small peasant farmer, and
his education was what he was able to secure at the village school,
supplemented by a course at the gymnasium at Tropau, finishing
with a year at Olmutz. After completing the course at the gymna-
sium, Mendel applied for admission to the Augustinian order of
the monastery of St. Thomas in Briinn, generally referred to as
the Konigskloster. In the school and in the gymnasium Mendel had
won distinction as a student, and on entering the monastery was
chosen to assist in the educational work of the religious order.

''^^jiMA^MniiC'fir°dK--vyr'::'::p,h^riirvii%-^^^^

i'i^^^rs-s^ip^.%'M&~fiiS$^^-^iji^^pf^

itleiijmkMiillimii

Plate XLII. Gregor Mendel, 1822-1884.

288

PLANT HYBRIDIZATION BEFORE MENDEL

In 1847 he was ordained priest, and in 1851, at the expense of
the establishment, he was sent to the University of Vienna, re-
maining there until 1853 as a student of mathematics, physics,
and biology. On returning to Briinn, he became a teacher, chiefly
of physics, in the local Technische Hochschule. It is reported that
he was unusually successful as a teacher. In 1868 he was chosen

Plate XLIII. The Augustinian Cloister at Briinn.

Abbot of the monastery at Briinn. The famous scientific investi-
gations connected with his name were conducted in the monastery
garden during the eight years preceding 1865. After his election
as Abbot in 1868, his scientific work ceased, and he became in-
volved in 1872 in a quarrel with the Austrian government, over
a law imposing a special tax upon the property of religious cor-
porations. This controversy, and others in which he became in-
volved, made the last ten years of his life a period of bitterness
and disappointment. On January 6, 1884, Mendel died at the age
of 62. In addition to his work with plants, Mendel conducted
experiments in the breeding of bees, securing queens of various

PLANT HYBRIDIZATION BEFORE MENDEL 289

races, and using some fifty hives for his experiments. Of these
experiments, no written record has survived.

Mendel was a man of keen scientific instincts in general. He was
interested in meteorology, and made a study of sun spots with ref-
erence to their relation to meteorological phenomena on the earth.
He kept meteorological records for many years, and practically un-
til his death. At least some of these records are published in the
Transactions of the Briinn Society. He served one term as president
of the Natural History Society of Briinn. That Mendel possessed
unusual business and administrative ability is evidenced by the
fact that he rose to the station of Abbot in his order, a position
which placed him in charge of the business affairs of the organ-
ization; and by the interesting fact that he was chosen chairman
of the Moravian Hypotheken-Bank of his city. A curious report
exists as to his ability as a chess player, and his love for chess
seems to be well established by statements of his associates in the
St. Thomas Cloister. Mendel was also good at bowling, and had
an alley, on the walls of which some of his scores are still
pointed out. That Mendel throughout his life possessed the spirit
of a leader and organizer is very clear. A minor circumstance bear-
ing upon this fact is the incident that in his native village of
Heinzendorf he is recalled as the organizer of a fire brigade. The
erection of a new fire station in the town, after Mendel's name
became famous, was the occasion for the placing of a memorial
tablet in the building.

Gregor MendeL however, died in 1884 — sixteen years before
his work of 1868 became known to the scientific world.

At the time when Mendel's paper on hybridization appeared,
scientific circles, and the intellectual world generally, were full
in the midst of the discussions and debates precipitated by the
publication in 1859 of Darwin's "Origin of Species," and of the
first edition of his "Variation of Anima^ls and Plants under Do-
mestication" in 1868. It is clear that Darwin had never seen
Mendel's paper, although Mendel was familiar with Darwin's
work. Indeed the only biologist of note with whom Mendel ap-
pears to have been in correspondence was Nageli. The corre-
spondence between them is published, but there is no evidence
that Nageli grasped the significance of Mendel's discovery. The

290 PLANT HYBRIDIZATION BEFORE MENDEL

only references to Mendel's paper in scientific literature before
1900, as already remarked, are the statements referred to above
in Focke and Hoffmann.

Mendel was led to undertake his investigations through a
realization that some law must underlie the fact of the regular
reappearance of the same types of hybrids zuhenever the same
two species are crossed.

He says :

"The striking regularity with which the same hybrid forms always re-
appeared whenever fertilization took place between the same species in-
duced further experiments to be undertaken, the object of which was to
follow up the development of the hybrids in their progeny." (5d, p. 335.)

". . . That so far no generally applicable law governing the formation
and development of hybrids has been successfully formulated can hardly
be wondered at by anyone who is acquainted with the extent of the
task, and can appreciate the difficulties with which experiments of this
class have to contend. A final decision can only be arrived at when we
shall have before us the results of detailed experiments made on plants
belonging to the most diverse orders." {ib., pp. 335-6.)

The kernel of Mendel's method, and the revelation of his scien-
tific insight, which so far outstripped that of all previous inves-
tigators in the field of hybridization, appears in the following
paragraph :

"Those who survey the work done in this department will arrive at the
conviction that, among all the numerous experiments made, not one has
been carried out to such an extent and in such a way as to make it pos-
sible to determine the number of different forms under which the off-
spring of hybrids appear, or to arrange these forms with certainty ac-
cording to their separate generations, or definitely to ascertain their
statistical relations." {ib., p. 336.)

As Bateson says :

"It is to the clear conception of these three primary necessities that the
whole success of Mendel's work is due. So far as I know this conception
was absolutely new in his day." {ib., p. 336, note.)

In the first place Mendel devoted great care to the selection
of a plant for his experiments, the requisites being, as he says,
the possession of constant differentiating characters, freedom
from accidental crossing by foreign pollen, and fertility of the
hybrids. No one before Mendel had apparently grasped the neces-
sity for the employment of the following method as outlined by
him:

PLANT HYBRIDIZATION BEFORE MENDEL 291

"in order to discover the relations in which the hybrid forms stand
toward each other, and also toward their progenitors, it appears to be
necessary that all members of the series developed in each successive
generation should be, without exception, subjected to observation." (th.^
P- 337.)

Mendel's attention was called to the Leguminosae as a possible
group for experimentation, because "of th^ir peculiar floral struc-
ture." (p. 337.) After making experiments with several members
of this family, he came to the conclusion that the genus Pisum
(pea) fulfilled his requirements. He investigated, during two
years, thirty-four more or less distinct varieties of peas obtained
from seedsmen. Twenty-two of these varieties "were selected and
cultivated during the whole period of the experiments. They re-
mained constant without an exception.'* (p. 338.)

Mendel concerned himself little with the supposed systematic
classification of his varieties of peas. The majority of them he
assigns to Pisum sativum, others to sub-species of this, and still
others to distinct species.

"The positions, however, which may be assigned for them in a classi-
ficatory system are quite immaterial for the purpose of the experiments
in question. It has so far been found to be just as impossible to draw a
sharp line between the hybrids of species and varieties, as between
species and varieties themselves." (p. 338.)

The earlier hybridizers of plants, for the most part, made a
distinction between "hybrids" so-called, between "species," and
"crosses" between "varieties." Mendel discards this terminology,
recognizing that the distinction is one of degree and not of kind,
a distinction essentially artificial when closely applied.

The fundamental difference between Mendel's hybridization
experiments and all others stands out most clearly in the follow-
ing statement :

"if two plants which differ constantly in one or several characters be
crossed, numerous experiments have demonstrated that the common
characters are transmitted unchanged to the hybrids and their progeny;
but each pair of differentiating characters, on the other hand, unite in
the hybrid to form a new character, which in the progeny of the hybrid
is usually variable. The object of the experiment was to observe these
variations in the case of each pair of differentiating characters, and to
deduce the law according to which they appear in the successive genera-
tions. The experiment resolves itself therefore into just as many sepa-
rate experiments as there are constantly differentiating characters pre-
sented in the experimental plants." (pp. 338-9.)

292 PLANT HYBRIDIZATION BEFORE MENDEL

The "characters" which Mendel, after careful consideration,
finally selected for his work were the following:

1. The form of the ripe seeds (i.e., of the ripe cotyledons), whether

(a) round, or (b) wrinkled.

2. The color of the ripe seeds (i.e., of the ripe cotyledons within the
transparent seed coats), whether (a) yellow, or (b) green.

3. The color of the seed coat, whether (a) gray or brown, with violet-
red flowers, or (b) white with white flowers.

4. The form of the ripe pods, whether (a) inflated, or (b) constricted,
between the seeds.

5. The color of the unripe pods, whether (a) green or (b) yellow.

6. The difference in the position of the flowers, whether (a) distributed
along the main axis, or (b) bunched at the top of the stem in a false
umbel.

7. The difference in length of stem, whether (a) 6-7 ft. in length, or

(b) ^^.y^ ft.

Each two "differentiating characters" as they are called, in the
seven pairs, were tested by crossing. It may be interesting to no-
tice how many crosses were actually made.

1st character-pair — 60 crosses on 15 plants

2nd " — 58 crosses on 10 plants

3rd " — ^35 crosses on 10 plants

4th " — 40 crosses on 10 plants

5th " — 23 crosses on 6 plants

6th " — 34 crosses on 10 plants

7th " — 37 crosses on 10 plants

In all the seven classes of cases, reciprocal crosses were made.

Mendel calls attention to the fact that previous experiments
with hybrids showed that, as a rule, hybrids were not exactly in-
termediate between their two parents, and that, with respect to
some of the cases,

". . . One of the two parental characters is so preponderant that it is
difficult, or quite impossible, to detect the other in the hybrid." (p, 342.)
"This," he adds, "is precisely the case with the pea hybrids. In the
case of each of the seven crosses, the hybrid character resembles that of
one of the parental forms so closely that the other either escapes obser-
vation completely or cannot be detected with certainty." (p. 342.)

The character which became evident in the hybrid, Mendel
called the dominant., and the character that remained latent, the
recessive. He calls attention to the fact that the dominant char-
acter is unaffected by the direction of the cross — that it makes no
difference whether the parent bearing the character that becomes
dominant in the hybrid is used as the pollen parent or as the

PLANT HYBRIDIZATION BEFORE MENDEL 293

seed parent. This interesting fact, as Mendel states, had already
been observed by Gartner (4), whose statement it may be worth
while to reproduce.

"This most important and most interesting phenomenon in the cross-
ing of plants for the production of hybrids is the complete similarity of
the two products ; in that seeds which come from the one as well as
from the other fertilization give rise to plants of the most complete
similarity ; so that the dissimilar origin and derivation of the two kinds
of hybrids, after the most careful investigation with respect to their
form and type, does not admit of the slightest distinction between them,
and even the most practised expert with a hybrid species is not in a
position to distinguish the origin of the hybrid with respect to the sex
of the parents. . . . This is the general rule with almost all plants."
(p. 223.)

Here it is well to call attention to the fact that Mendel never
for a moment considered, as did all the older hybridizers, that
he was crossing one individual as a whole with another as a
whole, but that he was pitting one character in an individual
against a single contrasting character in another individual.
Herein is revealed Mendel's scientific genius and analytical in-
sight.

In the seven classes of "character-crosses," if we may so desig-
nate them, that Mendel made with peas, he found that in the
first generation, the following characters were dominant.

Dominant Recessive

1. round seeds over wrinkled seeds •

2. yellow seeds " green seeds

3. gi^ey or brown seed-coats " white (i.e., colorless) seed-coats

4. inflated ripe pods " constricted ripe pods

5. immature green pods *' immature yellow pods

6. axial arrangement of " bunched or terminal arrangement
flowers of flowers

7. tall stems ** dwarf stems

Of these "characters," those relating to the shape and color of
the seeds (i.e., of the cotyledons within the seed-coats) can, of
course, be seen at once after the flowers have been fertilized, and
the seeds grown. All of the other characters, of seed coats, pods,
flowers and stems, can only, of course, become apparent when the
hybrid seedlings grow up and produce stems, flowers, pods, and
seeds themselves.

Mendel now proceeds with the study of the second generation
(F2). Of the self-fertilized hybrid he says:

294 PLANT HYBRIDIZATION BEFORE MENDEL

"In this generation there' re-appear, together with the dominant char-
acters, also the recessive ones with their peculiarities fully developed,
and this occurs in the definitely expressed average proportion of three
to one, so that among each four plants of this generation three display
the dominant character, and one the recessive. This relates without ex-
ception to all the characters which were investigated in the experiments.
The angular, wrinkled form of seeds, the green color of the albumen,
the white color of the seed-coats and the flowers, the constrictions of
the pods, the yellow color of the unripe pod, of the stalk, of the
calyx, and of the leaf venation ; the umbel-like form of the inflorescence,
and the dwarfed stem, all re-appear in the numerical proportions given
without any essential alterations. Transitional forms were not observed
in any experiment." (Italics inserted.) (p. 344.)

It will be interesting to give in this connection, the actual data
of the experiments themselves.

It is seen from the table on page 295, that the ratios throughout
are nearly or quite 3:1. In the two seed experiments, each pod
usually produced both kinds of seed. As Mendel says :

"in well-developed pods which contained on the average six to nine
seeds, it often happened that all the seeds were round or all yellow J
on the other hand there were never observed more than five wrinkled or
five green ones in one pod." (1, p. 344.)

The net result of Mendel's investigation of the Fo and the F.<
generations is expressed as follows :

"The ratio of 3 to 1, in accordance with which the distribution of the
dominant and recessive characters results in the first generation, resolves
itself therefore in all experiments, into the ratio of 1 pure dominant ;
2 hybrids ; 1 recessive, if the dominant character be differentiated accord-
ing to its significance as a hybrid character or as a parental one." {ib.,
p. 349.)

In other words, the 75 per cent of plants which show the domi-
nant form in the F2 generation were found by Mendel's analysis
(i.e., by growing them another year) really to consist of two
parts hybrids, which go on splitting In the original ratio of 3:1 ;
and one part pure dominants, which continue to breed true as
such.

Mendel summarizes the matter in the following significant
sentence :

"since the members of the first generation (F^) spring directly from
the seed of the hybrids (Fj), it is now clear that the hybrids form seeds
having one or the other of the two differentiating characters, and of
these, one-half develop again the hybrid form, while the other half yields
plants which remain constant, and receive the dominant or the recessive
characters respectively in equal numbers." (Italics as In original.) (p. 349.)

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296 PLANT HYBRIDIZATION BEFORE MENDEL

The matter may be simply outlined by the usual familiar dia-
gram. Supposing the case of plants bearing round, and plants
bearing wrinkled seeds; the dominant parent (round) being ex-
pressed by R and the recessive parent (wrinkled) by W, then:

(1) R X W Parents

(2)

Fi generation

(3)

R RW W

25% 50% 25%

Fo generation

(4)

R RW W

25% 50% 25%

etc.

Fa generation

In the above diagram it is assumed (and so it occurred in Men-
del's case) that the R's and RW's in (3) will all look alike — i.e.,
that they will all appear round, and hence will make up 75 per
cent of the total, while the other 25 per cent will be pure W's
or wrinkled's, and will appear as such. Now by growing self-
fertilized plants of the combined R's and RW's in (3) it will
come out in the F3 generation (4) that one-third of the combined
lot of R's and RW's of (3), i.e., 25 per cent of the whole number,
will breed true as R's, while the other two-thirds (50 per cent of
the entire number) will turn out to split up again in the ratio of
three R's, or rather of apparent R's, to one W — in other words,
the ratio that indicates their hybrid composition.

We can say, therefore, that in any case of simple Mendelian
hybrids, i.e., where one character-pair only is concerned, the
hybrid or F^ generation has always internally the following in-
visible composition, which can be revealed by breeding,

25% 50% 25%

pure dominant-recessive pure

dominant or hybrid (appearing recessive

dominant)

All these are bound together in the F^ generation under the
apparent uniformity which the dominant character imposes. Gen-
eralizing, and expressing the dominant by D and recessive by R,
we have :

D X R = DR

DR X DR=lDD :2DR: IRR

Thus far we have followed, in considerable detail, Mendel's
original experiments themselves. It is plain that these exhaustive

PLANT HYBRIDIZATION BEFORE MENDEL 297

and laboriously detailed experiments leave no doubt as to the
central facts of what we know as the "Mendelian" factor-analysis,
viz., that each germ cell or gamete carries what Mendel called
the dominant or the recessive character as the case may be, in
pure form; that, in the hybrids, the gametes carry the dominant
and the recessive characters respectively in equal numbers, so
that when they unite at random according to the law of chance,
they will produce all possible combinations in equal numbers as
follows :

Male gamete Tern ale gamete Zygote

1. D X D DD

2. D X R DR

3. R X D RD

4. R X R RR
This means that in any hybrid there exist equal numbers of

these four combinations, when a single opposing pair of char-
acters is involved, so that the result of all the four possible com-
binations will be :

25% 25% 25% 25%

DD DR RD RR

as the condition of things existing in any Mendelian monohybrid
(i.e., in which a single pair of characters only is considered), or,
as commonly expressed :

25% 50% ■ 25%

DD DR RR

We have seen that, with an increase in the number of character-
pairs, we simply increase the number of terms in the series, by
the formation of a combination series, in which each kind of char-
acter-combination of the one unites with each kind of character-
combination of the other series — a process which can be repre-
sented by the algebraic multiplication of

A + 2 Aa,+ a
by B + 2 Bb + b

We can do this, because A-f-^Aa-j-a is, as we have seen, the
series of segregated types which the F^ or hybrid generation, Dr
(expressing the recessive by a small letter), algebraically ac-
tually can and does form on self-fertilization. Likewise, with the
series B+2Bb-f-b, into which the hybrid Bb segregates on self-

298 PLANT HYBRIDIZATION BEFORE MENDEL

fertilization. The algebraic multiplication of these two series sim-
ply represents the fact that both B and b unite with A, lAa and
a and so on.

Since the segregation of the offspring of a self-fertilized hybrid
involving one pair of characters, a dominant D and recessive r,
gives us a total of 3 apparent D's to 1 r, or the familiar ratio
of 3:1, then two pairs of opposing characters, thus segregating,
would give a ratio of 9:3:3:1, which is plainly the result of
the combination of two 3 : 1 ratios, this being the result obtained
by multiplying together the ratios in w'hich each of the character-
combinations separately occurs. Taking, for example, the charac-
ters round (D) and wrinkled (r) : and yellow (D) and green (r) :

In the F2 generation, there are 3 yellows to 1 green in every 4,
and there are 3 round to 1 wrinkled in every 4.

Where both of these two sets of character-pairs are united in
the same hybrid, the numerical proportions of the character-
combinations, so far as appearances go, will necessarily then be
as follows :

Yellow and round 3X3 — 9

Yellow and wrinkled 3 X ' = 3

Green and round 1 X 3 — 3

Green and wrinkled 1 X 1 -— 1

In the detailed analysis we will have :

1. Yellow round

(1) pure as to color and form l

(2) pure as to color but not as to form 2

(3) pure as to form but not as to color 2

(4) hybrid in both respects 4

Yellow wrinkled

(1) pure as to color and form l

(2) pure as to form but not as to color 2

Green round

(1) pure as to both color and form 1

(2) pure as to color but not as to form 2

PLANT HYBRIDIZATION BEFORE MENDEL

299

4. Green wrinkled

(1) pure as to both color and form

Total number of types

We may now use the customary table of squares to represent
the possible number of zygote forms that are derived from a
given number of characters carried by the gametes.

Let us continue to take round and wrinkled, and yellow and
green as the character-pairs. We may then represent the F^ gen-
eration as being formed in the following way, where a plant bear-
ing the characters green and wrinkled is fertilized by pollen from
a plant bearing the yellow and round characters in its germ cells.

Male gametes
AB

Female
gametes

Likewise, let us suppose the reciprocal cross, where a plant
bearing yellow and round characters, is fertilized by pollen from
a plant bearing the characters green and wrinkled. We then have :

Male gametes
ab

Female

gametes

In both cases, as is plain, the zygote will theoretically have the
same character and appearance, AaBb. If we wish to show the
actual condition of things in the zygote, we may use the custom-
ary four-square table, indicating the dominant and recessive char-
acters by D and r.

300

PLANT HYBRIDIZATION BEFORE MENDEL

TABLE I

Male gametes
D

Female
Gametes

In this table we therefore see four kinds of gametes formed in
the hybrid zygote of the F^ generation. Let this hybrid be self-
fertilized, and we have, of course, each of the four types of male
gametes uniting with each of the same four types of female
gametes. The process may then be reproduced by a sixteen-square
table as follows :

TABLE II

Male gametes
aB

Female
gametes

AB
aB
Ab
ab

AA.BB

Aa.BB

AA.Bb

Aa.Bb

Aa.BB

aa.BB

Aa.Bb

aa.Bb

AA.Bb

Aa.Bb

AA.bb

Aa.bb

Aa.Bb

aa.Bb

Aa.bb

aa.bb

So far as appearances go, the plants resulting from these six-
teen combinations would be as follows :

TABLE III

YELLOW
ROUND

GREEN
ROUND

YELLOW
ROUND

GREEN
ROUND

YELLOW
ROUND

YELLOW
WRINKLED

YELLOW
ROUND

GREEN
ROUND

YELLOW
WRINKLED

GREEN
WRINKLED

PLANT HYBRIDIZATION BEFORE MENDEL 301

We have here 9 yellow round, 3 yellow wrinkled, 3 green
ROUND, and 1 green wrinkled. This is, to be sure, a table of
appearances only, or what are known as the "phenotypes." This,
then, is the way in which the plants or zygotes, formed by the
gametic union of one AaBb hybrid with another AaBb hybrid,
actually look. What they actually are is expressed in Table II.
We have in Table II a zygote AA.BB, produced by the combina-
tion of a gamete bearing the combination AB with a gamete bear-
ing the character-combination AB. Such an organism has been
called homozygous, the gametes forming it being alike for both
characters. At the end of the same row we find a zygote whose
constitution is AaBb, produced by a combination of a gamete AB
with a gamete ab, which combination is called heterozygous, the
gametes forming it being unlike for both characters of the two
pairs. We have also in the same rows, zygotes AABb, and AaBB,
which are heterozygous for color (Bb), in the first case, and for
form (Aa), in the second case. We may then have organisms that
are homozygous (i.e., alike) for both pairs of characters (DDrr) ;
homozygous for a single pair of characters (DD) and hetero-
zygous (i.e., unlike) for another pair (Dr) ; or heterozygous for
both pairs (DrDr). If the combinations in Table III, representing
the behavior of two character-pairs in fertilization, be compared
with Mendel's way of stating the combinations, using A and a
for round and wrinkled, and B and b for yellow and green, re-
spectively, differences will appear which should be explained.
According to Mendel's form of statement for example, wrinkled
yellow in the zygote is represented by Mendel as aBb. Plainly
this comes about as the result of the combination of a wrinkled
yellow gamete (aB), with a wrinkled green gamete (ab) using the
letter "a" but once for the character represented. Such a combina-
tion at the end of the second row in Table II as is now represented
by aa.Bb Mendel represented by aBb,. because, since the "a" char-
acters in the two gametes were alike, he felt no need of represent-
ing the character in the zygote by double letters. But since the
"B" character, uniting with the "b" character, gave a zygote char-
acter of double composition, he represents it by "Bb." At present,
it is of course the practice to represent the actual gametic condi-
tion in the zygote by giving the letters representing the full

302 PLANT HYBRIDIZATION BEFORE MENDEL

gametic composition. So that AXB is represented by AA.BB, not
simply by AB as in Mendel's terminology, and so on. Following the
expression introduced by Bateson in 1901, each member of an op-
posing pair of characters is spoken of as an "allelomorph," from the
Greek allelon (reciprocal) and morphe (form). Round and wrin-
kled are then "allelomorphs^'' and such character-pairs are re-
ferred to as " alleloinorphic" pairs. This terminology has, of
course, become practically universal.

It was Mendel's belief, and this belief has been confirmed by
the discoveries since made, that all fertilizations are of the same
character, and that the phenomena which we call ''Mendelian"
are really the general phenomena which occur in all unions what-
soever of sexual cells, whether of plants or of animals, including
man, where independently operating factors are concerned; in
other words, that the phenomenon called "Mendelian" is the uni-
versal condition in amphimixis. It is extremely interesting to note
the signally significant insight of Mendel's comment as follows:

"whether the variable hybrids of other plant species observe an entire
agreement must also be decided experimentally. In the meantime we may
assume that in material points an essefitial difference can scarcely occur,
since unity in the developmental plan of organized life is beyond dis-
pute." (5d, p. 375.) (Italics inserted.)

Mendel himself, in his later experiments of crossing the dwarf
Lima Bean {Phaseolus nanus) "with small white seeds," with the
Scarlet Runner Bean (Phaseolus multiflorus) with "large seeds
which bore black flecks and splashes on a peach-blossom-red
ground," found that the color combination in the seeds appeared
not to follow his law. Anticipating modern work, which has con-
firmed his hypothetical conclusion, he says:

"Even these enigmatical results, however, might probably be explained
by the law governing Pisum, if we might assume that the color of the
flower and seeds of Phaseolus multiflorus is a combination of two or
more entirely independent colors, which iiidividually act like any other
constant character in the plant" (Italics inserted.) (p. 367.)

Mendel concludes with a further significant statement (p. 370),
which is perhaps one of the most striking illustrations of antici-
patory analysis to be found in the entire paper, and which was
first actually and fully demonstrated by the work of Bateson with
Sweet Peas in 1905 and 1906.

PLANT HYBRIDIZATION BEFORE MENDEL 303

"whoever studies the coloration which results in ornamental plants
from similar fertilization can hardly escape the conviction that here
also the development follows a definite law which possibly finds its ex-
pression in the combination of several independent color characters."
(P- 370.)

This leads to a reference to the matter of what are com-
monly known as "unit characters." Whatever these unit character-
determinants or genes may be, they are probably of the nature of
factors, the release of the operation of which sets in train a series
of physiological changes, which ultimately wind up by producing
the visible structural characters in question, and which are seen
to function as units in the cross. This conception was, as a matter
of fact, Mendel's own. The fact, furthermore, that in the produc-
tion of many complex characters several factorial units may
share, Mendel himself also surmised.

Mendel's conclusion, then, from his peas hybrids is as fol-
lows ( 1 ) :

"It is now clear that the hybrids form seeds having one or other of
the two differentiating characters, and of these one-half develop again
the hybrid form, while the other half yield plants which remain constant,
and receive the dominant or the recessive characters (respectively) in
equal numbers." (p. 349.)

Since the offspring of hybrids split off or segregate to the extent
of one-half in each succeeding generation, an example of the result
in respect to the seeds is given by Mendel as follows:

Dr r Ratios

8
16
32

"in the tenth generation, for instance, 2'' — 1 = 1023. There results, there-
fore, in each 2,048 plants which are in-, this generation, 1,023 with the
constant dominant character, 1,023 with the recessive character, and only
two hybrids." (p. 350.)

Mendel thus demonstrated that the hybrid character originally
brought together by crossing cannot be "fixed" as a whole by
selection. Each succeeding generation of the close-fertilized prog-
eny will undergo a constant diminution of the number of the

Generation

120

496

1 :

120

15:

496

31:

2' 1:

2'- 1

304 PLANT HYBRIDIZATION BEFORE MENDEL

hybrids, according to a fixed and unalterable ratio, with the re-
sult that by the tenth generation, there will be a practical elimina-
tion of the hybrid condition in most cases, all of the progeny
having been segregated into various combinations of dominants
and recessives.

Hybrids in which tzuo pairs of characters are concerned : results of
MendeV s experiments,

Mendel next undertook to determine the behavior of hybrids in
which more than one differentiating pair of characters was con-
cerned. To determine what would happen in such a case, he under-
took two experiments ; in the one, the parents differed in the form
and in the color of the seed (i.e., of the cotyledons within the seed
coat), involving therefore two differentiating characters in each
cross. In the second experiment, the seeds of the two parents dif-
fered in form^ in color ^ and in the color of the seed coats : thus
involving three pairs of differentiating characters in each cross.

For convenience' sake, in the first experiment, Mendel used the
following symbols :

A. round seed form a. wrinkled seed form

B. yellow seed color b. green seed color

In the F^ generation all the seeds produced were round and
yellow, as would have been expected from the fact that round
when taken singly is dominant over wrinkled, and yellow when
taken singly is dominant over green.

The fifteen plants raised from these yellow round seeds, yielded,
however, four kinds of seeds^ 556 in all, distributed in the follow-
ing way :

Ratio (^approximate)

315 round and yellow AB 9

101 wrinkled and yellow aB 3

108 round and green Ab 3

32 wrinkled and green ab 1

All of these 556 seeds were sown in the following year. The
plants that came to maturity, were distributed with regard to the
kinds of seeds they bore, as follows :

PLANT HYBRIDIZATION BEFORE MENDEL

305

1. Sowing all the round yellow seeds mentioned above, 301 plants re-
sulted, which bore seeds in the following ways :

38 plants had round yellow seeds AABB

65 plants had round yellow and round

green seeds AABB and AAbb

60 plants had round yellow and wrinkled

yellow seeds AABB and aaBB

138 plants had round yellow, round green,

wrinkled yellow, and wrinkled green

seeds AABB, AAbb, aaBB and aabb

2. Sowing all the wrinkled yellow seeds above, 96 plants resulted,
which bore seeds in the following ways :

28 plants had wrinkled yellow seeds • aaBB

68 plants had wrinkled yellow and wrinkled

green seeds aaBB and aabb

3. Sowing all the round green seeds above, 102 plants bore seeds in
the following ways :

35 plants had round green seeds AAbb

67 plants had round green seeds and wrin-
kled green seeds AAbb and aabb

4. Sowing, all the wrinkled green seeds, 30 plants resulted which bore
seeds as follows :

30 plants had all wrinkled green seeds aabb

Combining all these results into a common table we find :

CLASS I

GROUP

NO. OF

PLANTS

FORMULA

APPEARANCE OF
SEEDS

ACTUAL COM-
POSITION OF
SEEDS

BEHAVIOR

1
2

3
4

35
28

AABB
AAbb
aaBB

aabb

round yellow
round green
wrinkled yel-
low
wrinikled green

round yellow
round green
wrinkled yel-
low
wrinkled green

constant
constant
constant
constant

Av.

CLASS II

GROUP

NO. OF

PLANTS

FORMULA

APPEARANCE OF
SEEDS

ACTUAL COM-
POSITION OF
SEEDS

BEHAVIOR

5
6

7
8

68
60
67

AABb
aaBb
AaBB
Aabb

round yellow

wrinkled yel-
low
round yellow

round green

round yellow
(green)

wrinkled yel-
low (green)

round (wrin-
kled) yellow

round (wrin-
kled) green

hybrid
hybrid

Av.

3o6 PLANT HYBRIDIZATION BEFORE MENDEL

CLASS III

GROUP

NO. OF

PLANTS

138

FORMULA

APPEARANCE OF
SEEDS

ACTUAL COM-
POSITION OF
SEEDS

BEHAVIOR

AaBb

round yellow

round (wrin-
kled) yellow
(green)

hybrid

Av.

138

The character enclosed in parentheses, according to Mendel's original
conception, is the latent one in the hybrid.

Mendel then observed that the whole of these different groups
of plants could be arranged into three different classes, as follows :

1. The first class included only groups 1, 2, 3, and 4, with the
signs AB, Ab, aB, and ab. It is evident that round yellow seeds
(AB) will come true, as both the characters are dominants of
different character-pairs; likewise with wrinkled green seeds (ab),
since both of these characters are recessives of different character-
pairs. So also round green seeds (AAbb) and wrinkled yellow
(aaBB) will also come true and be constant, since they combine
the dominant of one character-pair with the recessive of another.

2. The second class of plants includes groups Nos. 5, 6, 7, and
8, AABb, aaBb, AaBB, and Aabb.

The above groups, as Mendel puts it, "are constant in one char-
acter and hybrid in another, and vary in the next generation only
in the hybrid character." (p. 352.)

This means, for example, that the plants in group No. 5, which
bears the sign AABb, are round (A) and yellow (B) in appear-
ance, but since they bear also the hidden recessive character (b),
they are hybrid with respect to color.

Likewise with the plants in group 6, which bear seeds that all
appear wrinkled 3^ellow, but which are hybrid (Bb) as to color,
since the B and the b occur together.

3. Finally, the third class includes only group 9, in which 138
plants bear round yellow seeds so far as appearances go, but,
since Aa and Bb are confined together, it is apparent that these
seeds are not pure round, but hybrid round, and that the yellows
are not pure yellow but hybrid yellow.

Now, by comparing the average number of plants of the groups
in the three classes, we get a very close ratio of 1 :2:4, since the

PLANT HYBRIDIZATION BEFORE MENDEL

307

actual ratios of 32:65:138, approximate almost exactly to the
theoretical ratio of 33:65:132.

It therefore appears from the above analysis that there are, in
all, nine sorts of forms, as follows, and in the following propor-
tions :
AABB AAbb, aaBB aabb, 2AABb 2aaBb, 2AaBB, 2Aabb, 4AaBb

This expression is evidently a combination series, representing
the product of the algebraic expression

(AA4-2Aa+aa) X (BB+2Bb+bb),
and expresses the full number of possible combinations of germ
cells in the hybrids.

After having determined the behavior of the offspring of hy-
brids in which two pairs of characters were involved, Mendel pro-
ceeded to investigate the behavior of hybrids where three charac-
ter-pairs are introduced, e.g. :

1. Form of seeds, whether round or wrinkled,

2. Color of seeds, whether yellow or green,

3. Color of seed-coats, whether grey-brown or white.

As Mendel says (p. 353), "among all the experiments it de-
manded the most time and trouble."

From the 24 crosses made, 687 seeds were produced. From these,
in the succeeding year, he raised 639 plants which bore fruit. The
characters are indicated as before :

Dominant Recessive

A — round seeds a — wrinkled seeds

B — yellow seeds b — green seeds

C — grey-brown seed-coats c — white seed-coats

The character of the seeds borne by these plants was as follows

CLASS I

Formula

Appearance of the seeds

Group

8 plants

AABBCC

Group

AABBcc

Group

AAbbCC

Group

AAbbcc

Group

8 "

aaBBCC

Group

aaBBcc

Group

aabbCC

Group

aabbcc

round yellow grey
round yellow white
round green grey
round green white
wrinkled yellow grey
wrinkled yellow white
wrinkled green grey
wrinkled green white

Average 10

308 PLANT HYBRIDIZATION BEFORE MENDEL

CLASS II

Formula

Appearance of the seeds

Group

22 plants AABBCc

round yellow grey

Group

AAbbCc

round green grey

Group

25 '

aaBBCc

wrinkled yellow grey

Group

' aabbCc

wrinkled green grey

Group

AABbCC

round yellow grey

Group

18 '

AABbcc

round yellow white

Group

aaBbCC

wrinkled yellow grey

Group

' aaBbcc

wrinkled yellow white

Group

AaBBCC

round yellow grey

Group

18 '

AaBBcc

round yellow white

Group

AabbCC

round green grey

Group

16 '

Aabbcc

round green white

Average

CLASS III

Formula

Appearance of the seeds

Group

45 plants AABbCc

round yellow grey

Group

36 '

aaBbCc

wrinkled yellow grey

Group 23

38 '

AaBBCc

round yellow grey

Group 24

AabbCc

round green grey

Group 2^

AaBbcc

round yellow grey

Group

48 '

AaBbcc

round yellow white

Average 43

CLASS IV

Formula

Appearance of the seeds

Group 27 78 plants

AaBbCc

round yellow grey

CLASS I

Actual conditions as determined by breeding

Constant

«
«

((

Group
Group

1
2

round yellow grey
round yellow white

Group
Group
Group
Group
Group
Group

5
6

7
8

round green grey
round green white
wrinkled yellow grey
wrinkled yellow white
wrinkled green grey
wrinkled green white

PLANT HYBRIDIZATION BEFORE MENDEL

309

CLASS II

Group 9 round yellow grey (white)

Group 10 round green grey (white)

Group 11 wrinkled yellow grey (white)

Group 12 wrinkled green grey (white)

Group 13 round yellow (green) grey

Group 14 round yellow (green) white

Group 15 wrinkled yellow (green) grey

Group 16 wrinkled yellow (green) white

Group 17 round (wrinkled) yellow grey

Group 18 round (wrinkled) yellow white

Group 19 round (wrinkled) green grey

Group 20 round (wrinkled) green white

CLASS III

Hybrid

Group 21 round yellow (green) grey (white)

Group 22 wrinkled yellow (green) grey (white)

Group 23 round (wrinkled) yellow grey (white)

Group 24 round (wrinkled) green grey (white)

Group 25 round (wrinkled) yellow (green) grey

Group 26 round (wrinkled) yellow (green) white

CLASS IV

Hybrid

Group 27 round (wrinkled) yellow (green) grey (white) Hybrid

We have thus an expression with 27 terms or character-combina-
tions, the members of which manifestly fall into four classes.

Class I, of 8 terms, contains plants that are constant in all their
characters, as can be seen by inspection, since they all contain the
pure dominant or pure recessive of one character, united with a
pure dominant or a pure recessive of each of the other two. Each
of the character-combinations in Class I occurs on the average in
10 plants.

Class II has 12 terms or character-combinations, each of which
is constant for two characters, but inconstant or hybrid in the
third. This is illustrated by the combination AABBCc. The sym-
bols indicate that the seeds in this combination are round (AA),
yellow (BB), and grey-brown in the seed-coats (Cc). But the fact
that c is combined with C indicates that we have here not a pure
dominant (CC), but a hybrid (Cc). In other words, AABBCc is
constant for form and seed-color, but hybrid as to seed-coat color
alone (Cc). It will be noticed that the average number of plants
per character-combination in Class II is 19.

310

PLANT HYBRIDIZATION BEFORE MENDEL

Class III has 6 terms or character-combinations, with an average
of 43 plants to each such combination. All the groups in this class
are constant as to one character and hybrid as to the other two.
For example, Group 2i bears the sign AABbCc. This means that
the seeds of each of the 45 plants in this group had the following
appearance: they were all round (AA), yellow (Bb), and grey-
brown (as to seed-coat) (Cc). But since B is hybrid as to color of
the cotyledons, and since C is accompanied by c it is hybrid as to
seed-color and seed-coat color also.

Finally, Class IV has one term with 78 plants, each of which is
hybrid with respect to all three of the character-pairs.

The ratios in which the average of the plants in each class stand
to one another, of 10:19:43:78, are so close to 10:20:40:80,
or 1:2:4:8, that there is no doubt whatsoever that this is the
actual ratio.

It then appears that the actual condition of things in a hybrid,
in which three pairs of characters are in question, is a combina-
tion obtained by multiplying together the following expressions :

and

AA + 2Aa + aa,
BB + 2Bb + bb,
CC + 2Cc + cc.

The result is that we get all the possible combinations of these
various terms (or character-combinations), to the number of 27,
as follows :

AABBCC

2AAbbCc

2AabbCC

AABBcc

2aaBBCc

2Aabbcc

AAbbCC

2aabbCc

4AABbCc

AAbbcc

2AABbCC

4aaBbCc

aaBBCC

2AABbcc

4AaBBCc

aaBBcc

2aaBbCC

4AabbCc

aabbCC

2aaBbcc

4AaBbCC

aabbcc

2AaRBCC

•26

4AaBbcc

2AABBCC

2AaBBcc

SAaBbCc

Mendel did not stop here, however, but carried on further ex-
periments in which the remaining characters, i.e., pod-characters,
height, etc., were also combined by twos and threes, which he says
all gave approximately the same results. From these experiments
he concludes that :

PLANT HYBRIDIZATION BEFORE MENDEL 311

"There Is therefore no doubt that, for the whole of the characters in-
volved in the experiments, the principle applied that the offspring of the
hybrid in which several essentially different characters are combined ex-
hibit the terms of a series of combinations, in which the developmental
series for each pair of differentiating characters are united. It is demon-
strated at the same time that the relation of each pair of different char-
acters in hybrid union is independent of the other differences in the two
original parental stocks." (p. 354.)

The last sentence in the above is characteristic of Mendel's
type of experimental work, and demonstrates in small compass
the difference between his method of attack upon the problem of
heredity, and that of all of his predecessors.

Mendel concludes that, where two or more characters are com-
bined in a cross, the offspring of the resulting hybrids form the
terms of a series of combinations, in which each pair of differen-
tiating characters is present, either as a pure dominant, or a pure
recessive, or a hybrid dominant. Moreover, if there is :

One differentiating pair of characters in the parents, the number
of character-combinations, i.e., the number of terms of the series,
will be : 3^= 3.

If there are :

Two differentiating pairs of characters in the parents, the num-
ber of combinations will be : 3-= 9.

If there are :

Three differentiating pairs of characters in the parents, the
number of combinations will be : 3^= 27.

Hence, generalizing, where "n" differentiating pairs of char-
acters are present in the parents, the number of combinations will
be 3".

Moreover, the total number of individuals which constitute the
series will be 4", and the number of constant combinations will
be 2".

To apply this rule to the case which Mendel worked upon,
with three differentiating pairs of characters, we have:

^M z= 33 =: 27 (No. of possible character-combinations)
4« =3 43 =: 5^ (Individuals in the entire series)
2« z= 23 =: 8 (Constant character-combinations)

"All constant combinations," Mendel says, "which in peas are possible
by the combination of the said seven differentiating characters, were
actually obtained by repeated crossing. Their number is given by
1" — 128. Thereby is simultaneously given the practical proof that the

312 PLANT HYBRIDIZATION BEFORE MENDEL

constant characters which appear in the several varieties of a group of
plants, may be obtained in all the associations which are possible accord-
ing to the mathematical laws of combination, by means of repeated arti-
ficial fertilization!' (p. 355.)

Mendel now undertook to draw conclusions from his data. As

we have seen :

"The offspring of the hybrids of each pair of differentiating charac-
ters are, one-half, hybrid again, while the other half are constant in
equal proportions having the characters of the seed and pollen parents
respectively, if several differentiating characters are combined by cross-
fertilization in a hybrid, the resulting offspring form the terms of a
combination-series in which the combination series for each pair of dif-
ferentiating characters are united." (p. 356.)

Mendel then comes finally to these fundamental conclusions :

"So far as experience goes, we find it in every case confirmed, that
constant progeny can only be formed when the egg cells and the fertil-
izing pollen are of like character, so that both are provided with the
material for creating quite similar individuals, as is the case with the
normal fertilization of pure species. We must therefore regard it as cer-
tain that exactly similar factors must be at work also in the production
of the constant forms in the hybrid plants. Since the various constant
forms are produced in one plant or even in one flower of a plant, the
conclusion appears logical that in the ovaries of the hybrid, there are
formed as many sorts of egg cells, and in the anthers as many sorts of
pollen cells, as there are possible constant combination forms, and that
these egg and pollen cells agree in their internal composition with those
of the separate forms. Cp. 356.)

"In point of fact it is possible to demonstrate theoretically that this
hypothesis would fully suffice to account for the development of the
hybrids in the separate generations, if we might at the same time assume
that the various kinds of egg and pollen cells were formed in the hy-
brids on the average in equal numbers!' (Italics inserted.) (p. 357.)

It was necessary, however, to put these last conclusions to ex-
perimental proof.

We have seen from Mendel's results, that in any Y^ generation
of a hybrid, the ratio of the "impure" or hybrid type to either
of the pure types is as 2:1.

We have also seen that the whole of any Fo generation pro-
duced by self-fertilization of the originally formed hybrids of
the F^ generation, consisted of :

25% + 50% + 25%

pure impure pure

dominants dominants recessives

DD Dr rr

i.e., 1S% 20c

apparent D pure r

PLANT HYBRIDIZATION BEFORE MENDEL 313

If now both the male and the female germ cells bear the char-
acters of either the dominant or the recessive in equal numbers,
and cross at random, then

D X r = Dr

and
r X D = rD

Then, when the F^^ hybrid, which we have been calling Dr,
but which is also rD, produces its offspring by self-fertilization,
we should get four kinds of combinations of germ cells in equal
numbers as follows :

1. D X D =DD

2. D X r = Dr

3. r X D = rD

4. r X r = rr

i.e. 25% 25% 25% 25%

DD Dr rD rr

It is plain that this combination would be a germ-cell analysis
of the actual visible result already stated in the ordinary form
of a ratio.

25% 50% 25%

DD : Dr : rr

In order to prove his assumption, "that the various kinds of
egg and pollen cells were formed in the hybrids on the average
in equal numbers," Mendel carried out the following experiment.

He crossed two forms of peas which were different in both the
form and in the color of the seeds. Hence, following the symbols
previously used :

A round seeds a wrinkled seeds

B yellow seeds b green seeds

The Fi hybrids thus produced we>e sown, and there were also
sown seeds of both of the two parental types. AB and ab crosses
were then made as follows :

1. The Fi hybrids were crossed with pollen of AB (round yellow)

2. The Fi hybrids were crossed with pollen of ab (wrinkled green)

3. AB (round yellow) were crossed with pollen of Fj hybrids.

4. ab (wrinkled green) were crossed with pollen of F^ hybrids.

314

PLANT HYBRIDIZATION BEFORE MENDEL

All of the flowers on each of three plants were pollinated for
the purpose of this experiment.

We have seen that, on the basis of the theory already stated,
the offspring of an F^ hybrid, when one character-pair is involved,
should be : AB, Ab, aB, and ab, in equal numbers.

In the crossing experiment just undertaken, there would then
be the following combinations :

Series

1. Egg cells AB, Ab, aB, ab, X pollen cells AB

2. Egg cells AB, Ab, aB, ab, X pollen cells ab

3. Egg cells AB, X pollen cells AB, Ab, aB, ab

4. Egg cells ab, X pollen cells AB, Ab, aB, ab

There would then result combinations as follows :

Series

AABB

AABb

AaBB

AaBb

Aabb

aaBb

aabb

AABB

AABb

AaBB

AaBb

Aabb

aaBb

aabb

The appearance of the seeds and their actual composition would
be then as follows :

SERIES I

Formula

Appearance

Actual Composition

Behavior

AABB

round yellow

constant

AABb

round yellow

round yellow (green)

hybrid

AaBB

round yellow

round (wrinkled) yellow

hybrid

AaBb

round yellow

round (wrinkled) yellow

(green)

hybrid

SERIES II

Formula

Appearance

Actual Composition

Behavior

AaBb

round yellow

round (wrinkled) yellow

(green)

hybrid

Aabb

round green

round (wrinkled) green

hybrid

aaBb

wrinkled 3'ellow

wrinkled yellow (green)

hybrid

aabb

wrinkled green

SERIES III

constant

Formula

Appearance

Actual Com.position

Behavior

AABB

round yellow

AABb

round vellow

round yellow (green)

AaBB

round yellow

round (wrinkled) yellow

AaBb

round yellow

round (wrinkled) yellow
(green)

constant

hybrid

PLANT HYBRIDIZATION BEFORE MENDEL 315

SERIES IV

Formula

Appearance

Actual Composition

Behavior

AaBb

round yellow

round (wrinkled) yellow

(green)

hybrid

Aabb

round green

round (wrinkled) green

hybrid

aaBb

wrinkled yellow

wrinkled yellow (green)

hybrid

aabb

wrinkled green

constant

If, as Mendel assumed, the egg and pollen cells bore the differ-
ent characters of dominant and recessive in equal numbers, then
we would expect in each experiment, that the four combinations
would be produced in equal numbers.

It is plain, that in the first and third series all the seeds ap-
pear round and yellow.

In the second and fourth series, one lot would appear round
yellow, another round green, another wrinkled yellow, and a
fourth wrinkled green.

The actual experiment bore out the theoretical expectation.

Appearance
No. of seeds of seeds

Series i yielded 98 round yellow
Series 2 yielded 31 round yellow

26 round green ■

27 wrinkled yellow

26 wrinkled green
Series 3 yielded 94 round yellow
Series 4 yielded 24 round yellow

25 round green

22 wrinkled yellow

27 wrinkled green

It is clear thus far, as to the outcome in series 2 and 4. In
both cases, the four different possible, combinations were produced
in equal numbers. It now remained to determine the actual com-
position of the 98 and 94 seeds in the firsthand third series, re-
spectively. All of the seeds of each of these two series were sown.
From the 98 seeds of Series I, 90 plants resulted, and from the
94 seeds of the second series, came 87 plants.

These all yielded as follows :

3i6 PLANT HYBRIDIZATION BEFORE MENDEL

No. of seeds Composition Formula

Series I yielded 20 round yellow AABB

23 round yellow (green) AABb

25 round (wrinkled) yellow AaBB

22 round (wrinkled) yellow (green) AaBb

Series III yielded 25 round yellow AABB

19 round yellow (green) AABb

22 round (wrinkled) yellow AaBB

21 round (wrinkled) yellow (green) AaBb

This means that, when all of the 90 plants in Series I ran to
seed, 20 of them yielded all round yellow seeds ; 23 plants yielded
yellow and green seeds in a ratio of 3 : 1, and thereby showed that,
although looking round yellow^ their actual composition was
round yellow {green) AABb. Likewise, there were 25 that yielded
round yellow and zorinkled yellow in the ratio of 3:1, thereby
proving that their original composition, although they also all
looked round yellow^ was actually round {wrinkled) yellow.,
AaBB. The same hybrid condition {for both character-pairs) was
also shown to exist for the 22 seeds of the 90 plants in Series I,
which split up into plants bearing partly wrinkled and green
seeds as recessives, thus revealing the original composition of
these 22 seeds sown to be AaBb.

The analysis having been made clear for Series I and III, let
us turn back to Series II and IV, and see what their actual com-
position turned out to be. Mendel found as follows :

SERIES II

The 31 round yellow seeds yielded plants with round (wrinkled) yellow

(green) seeds — AaBb
The 26 round green seeds yielded plants with round (wrinkled) green

seeds — Aabb
The 27 wrinkled yellow seeds yielded plants with wrinkled yellow

(green) seeds — aaBb
The 26 wrinkled green seeds yielded plants with wrinkled green seeds

— aabb

SERIES IV

The 24 round yellow seeds yielded plants with round (wrinkled) yellow

(green) seeds — AaBb
The 25 round green seeds yielded plants with round (wrinkled) green

seeds — Aabb
The 22 wrinkled yellow seeds yielded plants with wrinkled yellow (green)

seeds — aaBb
The 27 wrinkled green seeds yielded plants with wrinkled green seeds

— aabb

PLANT HYBRIDIZATION BEFORE MENDEL 317

From all of which it appears that the actual composition of the
seeds of the four series was as follows, summarizing :

Series I

AABB

Series III

AABB

AABb

AaBB

AaBb

Series II

AaBb

Series IV

AaBb

Aabb

aaBb

aabb

It is now perfectly plain that the crossed plants in the four
series gave, in each serves,, all four of the theoretically possible
combinations for the series, and in equal numbers throughout.

It is also plain that Series I and III, which are reciprocals, are
alike, and that Series II and IV, which are also reciprocals, are
also alike in the composition of their seeds.

This would have seemed sufficient to prove the correctness of
Mendel's theory, that the pollen and egg cells of the hybrids
carry the dominant and the recessive characters in equal numbers,
and that consequently, in self -fertilized hybrids, all the possible
combinations of the unitary characters called "dominant''' and
"recessive" are to be found in the pollen and egg cells in equal
numbers.

Mendel did not rest content, however, with the demonstration
which the experiment with the seed characters alone afforded. He
likewise experimented with the characters of flower-color and
length of stem, conducting the experiment so that, in the third
year of the investigation, each character ought to appear in half
of the plants, if the theory were correct.

Using violet-red flower color as against white, and long stem as
against short, he had 166 plants to flower in the third year, dis-
tributed as follows :

No. of plants

47
40

It is plain that the result is the same in kind as Mendel obtained
with the seed-characters. Even in addition to the experiments al-
ready carried out, Mendel further says :

'ass

Color of flower

Stem

violet-red

long

white

long

violet-red

short

white

short

3i8 PLANT HYBRIDIZATION BEFORE MENDEL

"For the characters of form of pod, color of pod, and position of
flowers, experiments were also made on a small scale, and results ob-
tained in perfect agreement. All the differentiating characters duly ap-
peared, and in nearly equal numbers." (p. 361.)

It is therefore evident that Mendel was justified in arriving at
the conclusions :

"Experimentally, therefore, the theory is confirmed, that the pea hy-
brids form egg and pollen cells which, in their constitution, represent
in equal numbers all constant forms which result from the combination
of the characters united in fertilization." (p. 361.)

"The law of combination of different characters which governs the
development of the hybrids finds therefore its foundation and explana-
tion in the principle enunciated, that the hybrids produce egg cells and
pollen cells which in equal numbers represent all constant forms which
result from the combination of the characters brought together in fer-
tilization." (p. 364.)

Mendel finally concludes this memorable paper with a brief
account of crossing experiments with a Pole Garden Bean, Phase-
olus vulgaris, growing 10 to 12 feet in height, and Phaseolus
nanus, a dwarf variety. Phaseolus vulgaris had yellow pods con-
stricted when ripe, and Phaseolus nanus green pods inflated when
ripe. Mendel found that tall stems, green pod-color, and inflated
pod-form were dominant over short stems, yellow color, and con-
stricted pod-form.

This concludes a rather full account and analysis of Mendel's
celebrated report on the behavior of hybrids. Nothing in any
wise approaching this masterpiece of investigation had ever ap-
peared in the field of hybridization. For far-reaching and search-
ing analysis, for clear thinking-out of the fundamental principles
involved, and for deliberate, painstaking, and accurate follow-
ing-up of elaborate details, no single piece of investigation in this
field before his time will at all compare with it, especially when
we consider the absolute absence of precedent and initiative for
the work. In a way, Darwin's experimental work in the crossing
of plants resembles it. Indeed, when we regard Mendel's work in
the light of its pioneer quality, exhaustive mastery of details,
marshalled throughout with reference to a fundamental motive
that was never lost sight of, we may well find no comparison for
Mendel's work than with that of Darwin.

PLANT HYBRIDIZATION BEFORE MENDEL 319

BIBLIOGRAPHY

1. Bateson, William.

Mendel's Principles of Heredity, Cambridge, 1902 : reprint

1913-

2. Correns, Carl.

(a) G. Mendels Regel iiber das Verhalten der Nachkom-
menschaft der Rassenbastarde. Berichte der deutschen
botanischen Gesellschaft, 18, Heft 4, 158, 1900.

(b) Gregor Mendels "Versuche iiber Pflanzenhybridem,"
und die Bestatigung ihrer Ergebnisse durch die neuesten
botanischen Untersuchungen. Botanische Zeitung,
58:229, 1900.

3. De Vries, Hugo.

(a) Sur la loi de disjonctlon des hybrides. Comptes Rendus,
130:845-7, March 26, 1900.

(b) Das Spaltungsgesetz der Bastarde. Berichte der deut-
schen botanischen Gesellschaft, 18:83, 1900.

(c) Sur les unites des caracteres specifiques, et leur applica-
tion a I'etude des hybrides. Revue Generate de Botan-
ique, 12 :257, 1900.

4. Gartner, Carl Friedrich von.

Versuche und Beobachtungen iiber die Bastarderzeugung im
Pflanzenreich. Stuttgart, 1849.

5. Mendel, Gregor.

(a) Versuche iiber Pflanzenhybriden. Verhandlungen Natur-
forschenden Vereines in Briinn, 10:1, 1865. Reprinted
1910.

(b) Reprinted in Flora, 1901, p. 364.

(d) English translation in "Mendel's Principles of Hered-
ity," by W. Bateson, pp. 335-386. Cambridge and New-
York, 1913.

6. Tschermak, Erich von.

tjber kiinstliche Kreuzung bei Pisum sativum. Zeitschrift fiir
das landwirtschaftliche Versuchswesen in Oesterreich. Jahr-
gang 3. Heft. 5, 1900.

CHAPTER XI

34. The Discovery of MendeVs Papers.

THE re-discovery of Mendel's papers was announced in
the three following contributions ; during the months of
March and April, 1900 :

De Vries, Hugo.

1. Das Spaltungsgesetz der Bastarde (Vorlaufige Mittheilung).
Article No. 11, in Berichte der deutschen botanischen Gesell-
schaft, \'ol. 18, pp. 83-90. (Received for publication, March
14, 1900.)

2. Sur la loi de disjonction des hybrides. Note de M. Hugo De
Vries, presentee par M. Gaston Bonnier, Comptes Rendus de
I'Academie des Sciences, Paris, Vol. 130, pp. 845-7. (Received
for publication ?vlarch 26, 1900, but appearing in publication
before the preceding.)

A further paper of significance is the following :

3. tjber erbungleiche Kreuzungen ( \'orlaufige Mittheilung). Arti-
cle No. 53, in Berichte der deutschen botanischen Gesellschaf r,
\'ol. 18, pp. 435-43. (Received for publication November 21,
1900.)

Correns^ C.

G. Mendels Regel iiber das \'erhalten der Nachkommenschaft
der Rassenbastarde. Article No. 19 in the Berichte der deut-
schen botanischen Gesellschaf t, Vol. 18, pp. 1 58-68. (Received
for publication, April 24, 1900. Dated Tiibingen, April 22,
1900.)

Tschermak, E. von.

1. Uber kiinstliche Kreuzung bei Pisum sativum. Article no. 26.

Berichte der deutschen botanischen Gesellschaft, Vol. 18, pp.

232-9. (Received for publication, June 2, 1900.)

PLANT HYBRIDIZATION BEFORE MENDEL 321

2. tJber kiinstliche Kreuzung bei Pisum sativum^ Zeitschrift fiir
das landwirtschaftliche Versuchswesen in Oesterreich. 3 Jahr-
gang, Heft. 5, pp. 465-555» 1900.

Of the three authors, priority in respect of publication of re-
sults lies with Hugo De Vries, then Professor of Botany at the
University of Amsterdam (now retired), in his paper, "Das Spal-
tungsgesetz der Bastarde," constituting Article No. 11 of Vol. 18,
of the Berichte der deutschen botanischen Gesellschaft. (Received
for publication March 14, 1900.)

The second in order of publication was that of Professor Carl
Correns, then Professor of Botany at the University of Tubingen,
now Director of the Kaiser Wilhelm Institut fiir Biologic, Berlin-
Dahlem, in Article 19, of Vol. 18 of the Berichte der deutschen
botanischen Gesellschaft. (Received for publication, April 24,
1900.)

Third in publication was the paper of Dr. Erich von Tscher-
mak, now Professor in charge of the Lehr-Kanzel fiir Pflanzen-
ziichtung, at the Hochschule fiir Bodenkultur at Vienna ; pub-
lished in Vol. 18, pp. 232-9, of the Berichte der deutschen botani-
schen Gesellschaft. Received for publication June 2, 1900, and
followed by a paper of the same title as above, given in the
Zeitschrift fiir das landwirtschaftliche Versuchswesen in Oesterr-
eich, 3 Jahrgang, Heft. 5, pp. 465-555.

Following are the statements by the three discoverers of Men-
del's epoch-making paper of investigation, as to the manner of
its discovery by them individually. These reports are in the form
of letters to the author, written on request, for inclusion herein.
The communication of De Vries is in^ English ; those of Correns
and von Tschermak are in German, and are translated for publi-
cation. A portion of the Correns report is taken from the article
entitled "Etwas iiber Gregor Mendel's Leben und Wirken" in Die
Naturwissenschaften, Jahrgang 10, Heft 29 (July 21, 1922),
pp. 629-31, kindly also sent by Professor Correns. Further data
are supplied from letters to the author.

Plate XLIV. Professor Hugo De Vrles, University of Amsterdam (retired).

PLANT HYBRIDIZATION BEFORE MENDEL 323

De Vries {letter of December 18, 1924) :

"when preparing my book on the Mutation Theory, I worked on the
basis of Darwin's Hypothesis of Pangenesis, and of the version of it
proposed in my Intracellular Pangenesis. The main principle of Pan-
genesis is the conception of unit characters. This led on the one side to
the theory of the origin of species by means of mutations, and on the
other to the description of the phenomena of hybridization as recom-
binations of these units. In 1893, I crossed Oenothera lamarckiana with
O. lam. brevistylis, and found their progeny to be uniform, and true to
the specific parent in 1894, but splitting in the second generation 1895,
giving 17-26 individuals with the recessive character (Mut. The. 11, p.
157). Many other species were tried with the same result, and dihybrid
crosses showed the laws of chance to be valid for them also. After finish-
ing most of these experiments, I happened to read L. H. Bailey's 'Plant
Breeding' of 1895.1 In the list of literature of this book, I found the
first mention of Mendel's now celebrated paper, and accordingly looked
it up and studied it. Thereupon I published in March 1900 the results of
my own investigations in the Comptes Rendus de I'Academie des Sciences,
T. CXXX, p. 845, under the title of 'Sur la loi de disjonction des hybrides,'
and shortly afterwards, in the same year, in the Berichte der deutschen
botanischen Gesellschaft, T. XVIII, p. 83, (March 14, 1900). A full account
of my experiments was given in the second volume of the German edi-
tion of my Mutation Theory, 1903."

The paper of De Vries, "Sur la loi de disjonction des hybrides,"
appearing in the Comptes Rendus for March 26, 1900, states
quite briefly results similar to those of Mendel, but obtained an-
terior to the author's re-discovery of the Mendel paper.

Although from the printed volumes of the Comptes Rendus
and of the Berichte d. d. bot. Gesellschaft it appears that the
longer and fuller article, in German, in the latter, was received

1 Professor Bailey's account of the manner in which the reference to
Mendel's paper came to be included in his book on "Plant Breeding," is
found in a footnote to "Plant Breeding" by L. H. Bailey, 4th ed., 1908,
p. 15" 5", as follows :

"The following extract from a recent letter from Professor De Vries
(printed here by permission) will explain the reference in the text. 'Many
years ago you had the kindness to send me your article on Cross-Breeding
and Hybridization, of 1892; and I hope It will interest you to know that
it was by means of your bibliography therein that I learnt some years
afterwards of the existence of Mendel's papers, which now are coming
to so high credit. Without your aid I fear I should not have found them
at all.' " Professor Baily concludes :

"My reference to Mendel in the bibliography referred to was taken
from Focke's writing. I had not seen Mendel's paper. The essay, 'Cross-
Breeding and Hybridization,' forms Chapter II of the present book; but
the bibliography that accompanies it was not printed until the second
edition of the book."

324 PLANT HYBRIDIZATION BEFORE MENDEL

for publication first, March 14, 1900, yet the brief two-page
article in French in the Comptes Rendus, dated March 26, 1900,
was the first actually to appear.

In the Comptes Rendus article, no mention is made of Men-
del's paper, but the author's own results are given. In the article
in the Berichte, however, Mendel's paper is discussed, and the
author's own results in harmony therewith are given in detail.

Following are abstracts of the three principal papers of De
Vries concerned with the Mendelian discovery: '

a. De Vries ^ Hugo.

Sur la loi de disjonction des hybrides.

Comptes Rendus, T. 130, pp. 845-7, 1900- (lb.)
The author cites from his Intracellular Pangenesis, 1889, the
principle enunciated that the

". . . specific characters of organisms are composed of very distinct units.
One is able to study experimentally these units, either in the phenomena
of variability, of mutability, or by the production of hybrids. In the lat-
ter case, one chooses by preference hybrids whose parents are not dis-
tinguished among themselves except by a single character (mono-hybrids),
or by a small number of characters, well delimited, and from which one
does not consider but one or two of these units, while leaving the others
to one side." {ib., p. 845.)

"Ordinarily hybrids are described as participating at the same time in
the characters of the father and of the mother. In my opinion one ought
to admit, in order to understand this fact, that the hybrids have,
some of them, the simple characters of the father, and others characters
equally simple of the mother. But when the father and the mother are
not distinguished except in a single point, the hybrid could not hold
the mean between thern ; because the simple character should be consid-
ered as a non-divisible unit." {ib., p. 845.)

"The hybrid shows always the character of one of the two parents,
and that always in all its force ; never is the character of one parent,
which to the other is lacking, found reduced by half." {ib., p. 845.)

"Ordinarily," De Vries comments, "it is the character of the species
which supervenes over that of the variety, or the older character over
the younger. . . . But," he adds, "I have observed diverse exceptions to
these rules." {ib., p. 845.)

De Vries then adds :

"In the hybrid, the simple differentiating character of one of the par-
ents is then visible or dominant ; while the antagonistic character is in a
latent or recessive state." {ib., p. 845.)

"The antagonistic characters remain ordinarily combined during the
vegetative life, these dominant, the others latent. But in the generation
period they are disjoined. Each grain of pollen and each oosphere re-
ceives but one of the two." {ib., p. 845.)

PLANT HYBRIDIZATION BEFORE MENDEL

The important statement then follows :

325

"For monohybrids, one has then the proposition that their pollen and
their ovules are no longer hybrids, that they have the character pure of
one of the parents, and the same proposition may be sustained for the
others (di- and polyhybrids), when one considers each time but a single
simple character." {ib., p. 846.)

"From this principle one is able to deduce nearly all the laws which
govern the distribution of characters of hybrids." {ib., p. 846.)

De Vries then gives a table of eleven species, from which, when

cross-fertilized, he found : •

". . . for the products, the following proportion of individuals presenting
the recessive characters." {ib., p. 846.)

Proportion of

hybrid with the

Parent having the dominant

Parent having the

recessive

character

recessive character

character

Agrostemma githago

A. nicaeensis

Chelidonium majus

C. laciniatum

Coreopsis tinctoria

C. brunnea

Datura tatula

D. stramonium

Hyoscyamus niger

H. pallidus

Lychnis diurna (red)

L. vespertina (white)

Lychnis vespertina (pubescent)

L. glabra (smooth)

Oenothera lamarckiana

0. brevistylis

Solanum nigrum

S. chlorocarpum

Trifolium pratense

T. album

Veronica longifolia

V. alba

From these results he deduced the conclusion:

"We see the recessive character is always near 25 per 100." {ib., p. 846.)

The author then goes on to state that :

"The cultivation of a further generation permits making a distinction
among the 75 per 100 individuals presenting the dominant character."

He then cites the results with a poppy having a black basal
spot upon the petals, with one having a white spot. Calling the
former N, and the latter B, he obtained, as for the preceding,
75 per cent N and 25 per cent B, in" the hybrids of the first gen-
eration. From the seeds of these hybrid plants, self-fertilized and
sowing the seeds from each plant in a separate plot, he obtained
for 25 out of the 75 plants bearing N, a pure progeny with black
petals, and for the 50 others, a mixture of plants with black
petals, and of plants with white petals, In the proportion of 37.5 N
to 12.5 B. He concludes:

326 PLANT HYBRIDIZATION BEFORE MENDEL

"We then have, summarizing the results of the two successive cultures :

400 hybrid seeds of N and B.

25 B

37-5 N ,,.^B

(Diagram inserted.)

De Vries further adds :

"l have, thus far, studied two other successive generations of these
same hybrids. They have repeated each time the same phenomenon of
disjunction.

"I have obtained the same results with the hybrids of sugar maize and
of starchy maize, in which the endosperms are visibly hybrid at the
same time as the embryo." {ih., p. 847.)

He then states a general conclusion as follows :

"One may condense the ensemble of these results by supposing that
the two antagonistic qualities, dominant and recessive, are disposed in
equal parts, in the pollen as in the ovules.

"if one calls D the grains of pollen or the ovules having a dominant
character, and R those which have the recessive character, one may rep-
resent the number and nature of the hybrids by the following repre-
sentative formula in which the numbers D and R are equal :

(D + R) X (D + R) = D2 + 2DR + R2

"This amounts to saying that there will be 25 per 100 of D, 50 per 100
of DR and 25 per 100 of R.

"The individuals D will have the dominant character pure, having in-
herited it from the father and from the mother. In the same manner,
the individuals R will have the recessive character pure, while DR will
be hybrids. These will carry the dominant character apparent and the
recessive character latent.

"One will not be able to distinguish the 25 per 100 D from the 50 per
100 DR, except by a second culture." {ib., p. 847.)

De Vries' final conclusion is :

"The ensemble of these experiments puts then In evidence the law of
the disjunction of hybrids, and confirms the principle I have enunciated
upon the specific characters considered as distinct units." {ib., p. 847.)

The next paper to be considered is ;

PLANT HYBRIDIZATION BEFORE MENDEL 327

De Vries :

Das Spaltungsgesetz der Bastarde.

Ber. d. d. bot. Ges., VoL 18, pp. 83-90. (la).
In this communication, De Vries again cites his Intracellular
Pangenesis (pp. 60-75) ^^^ ^^^ original thesis, that:

"The whole character of the plant is built up of definite units. These
so-called elements of the species, or elementary characters, one thinks of
as bound to material carriers. To each individual character there corre-
sponds a special form of material carrier. Transitions between these ele-
ments are as little found as between the molecules of chemistry." (la,
p. 83.)

De Vries then goes on to say :

"In this latter domain [i.e., that of hybrids], it demands a complete
changing about of the views from which investigation has to proceed.

"Nowhere as clearly as here [i.e., in the experiments on crossing and
hybridization] does the image of the species appear in contra-distinction
to its composition out of independent factors in the background." (Intra-
cellular Pangenesis, German ed., 1889, p. 25.)

De Vries then comments on the fact that the tlien existing
doctrine regarding hybrids regards species, sub-species, and vari-
eties, as the units, the combination of which form hybrids, a
distinction being made between crosses of varieties, and the true
hybrids of species, (la, p. 84.)

This attitude is, according to his views, to be given up for
physiological investigation, (la, p. 84.)

"in its stead is to be placed the principle of the crossing of species-
characters. The units of species-characters are accordingly to be re-
garded and studied as sharply separated magnitudes. They are to be
treated as being independent of one another everywhere, and as long
as no grounds for the contrary are apparent. In every crossing experi-
ment, there is accordingly only one character, or a definite number of
such, to be taken into observation : the remainder may, for the time, be
left out of consideration. Or rather it is indifferent whether the parents
differ from one another in still other points. For the experiments, how-
ever, manifestly the hybrids, both of whose parents differ only in the
one character, form the simplest cases [monohybrids in contrast to di- and
polyhybrids]."

If the parents of a hybrid diverge from one another in only
one point, or If one takes one or a few of their points of differ-
ence Into consideration, then they are In these characters an-
tagonistic. In all others alike, or, for the calculation. Indifferent ;
the crossing experiment will therefore be limited to the antagonis-
tic characters.

328 PLANT HYBRIDIZATION BEFORE MENDEL

"My experiments," he says, "have led me to the following principles :

1. "O/ the two antagonistic characters, the hybrid carries only the one
and, indeed, in complete expression. It is accordingly in this point not
to be distinguished from one of the two parents. Intermediates do not
occur.

2. "0/2 the formation of the pollen and egg cells the two antagonistic
characters separate. They follow accordingly, in the majority of cases,
simple laws of probability. These two principles, in the most essential
points, have already been propounded a long time since by Mendel, for
a special case (peas). They passed, however, again into oblivion, and
were misunderstood. They obtain generally according to my experiments,
for true hybrids.

"The lack of intermediates, between any two simple antagonistic char-
acters in the hybrids, is perhaps the best proof that such characters are
indeed delimited units, (la, pp. 84-5.)

"That polyhybrids so often represent intermediate forms, rests mani-
festly upon the fact that they have inherited a part of their characters
from the father, another part from the mother. With monohybrids, such,
however, is not possible.

"of the two antagonistic characters, that visible in the hybrid is the
dominating, the latent is the recessive." {ih., p. 85.)

In regard to Mendel's paper, De Vries remarks further in a

footnote (la, p. 85) :

"This important treatise Is so seldom cited, that I myself for the first
time came to know about it after I had closed the majority of my ex-
periments, and had derived therefrom the principles contributed in the
text."

The italics are Inserted, In order to call more definite attention
to this very important fact. In view of the almost parallel nature
of the conclusions of De Vries with those arrived at bv Mendel
himself.

In the following section of his paper, De Vries goes on to
state (p. 85) :

"in the hybrid, the two antagonistic characters lie near one another as
primordia. In vegetative life only, the dominating one is ordinarily visi-
ble. Exceptions are seldom." {ib., p. 86.)

As such De Vries cites the case of Veronica longifolia (blue)
X V' longifolia {alba\ in which Inflorescences occur, the flowers
of which are white on the one side, and blue on the other. Such
cases De Vries calls sectional splittings (sectionale Spaltungen).

Continuing, it is stated as to the primordia of the antagonistic

characters :

"On the formation of the pollen grains and egg cells, they separate.
The individual pairs of antagonistic characters behave at that time inde-
pendently of one another."

From this separation results the law :

PLANT HYBRIDIZATION BEFORE MENDEL

3^9

"The pollen grains and egg cells of the monohybrids are not hybrids,
but belong purely to the one or the other of the two parental types. For
di-polyhybrids the same holds good, in relation to every character re-
garded by itself." {ib., p. 86.)

De Vries then proceeds to the now well-known statement of

the situation in a hybrid, as regards the pollen and egg cells, in

the representation of the dominant and the recessive characters,

which is substantially as previously stated by the author in the

Comptes Rendus, except for the addition of the following general

statement :

"in the simplest case, the splitting manifestly occurs in equal halves,
and one gets :

50% dom. + 50% rec. pollen grains,
50% dom. + 50% rec. egg cells." (p. 86.)

For the existence of 75 per cent with the dominant and 25 per
cent with the recessive character among the progeny of a mono-
hybrid, De Vries adduces data from his own experiments with a
considerable number of species. He says :

"This composition I found to be verified in very many experiments."
{ib., p. 87.)

In addition to the crosses reported In the Comptes Rendus, De
Vries cites the following ratios, giving in each case the year of
the cross. Some of these were also given in the brief note in the
Comptes Rendus.

1. A. BY ARTIFICIAL CROSSING

Rec. %

year

Dominating

Recessive

of the
cross

Agrostemma githago

A. nicaeensis

1898

Chelidonium majus

C. laciniatum

1898

Hyoscyamus niger

H. pallidus

1898

Lychnis diurna (red)

L. vespertina (w

hite)

1892

Lychnis vespertlna (pubescent)

L. glabra (smooth)

1892

Oenothera lamarckiana

0. brevistylis

1898

Papaver somniferum (Mephisto)

P. (Danebrog)

1893

Papaver somniferum nanum

P., somniferum nanum

1894

(single)

(double)

Zea mays (starchy)

Zea mays saccharata

1898

Aster tripolium

A. album

1897

chrysanthemum roxburghi

C. album

1893

(yellow)

Coreopsis tinctoria

C. brunnea

1896

Solanum nigrum

S. chlorocarpum

1894

Veronica longifolia

V. alba

1894

viola cornuta

V. alba

1899

330 PLANT HYBRIDIZATION BEFORE MENDEL

The mean for all the experiments is given as 24.93 per cent.

De Vries adds further :

"The experiments comprise ordinarily a few hundred, sometimes about
1,000 individuals. With many other species I obtained corresponding re-
sults." (la, p. 87.)

The analysis of the 75 per cent apparently dominant follows :

"The distinguishing of the remaining 75% in the two groups cited is
much more troublesome. It requires that a number of individuals with
the dominating character be fertilized with their own pollen, and that,
in the next year, for every plant, the progeny be cultivated and counted.
This was carried out in 1896 for Papaver somniferuin (Mephisto) X Dane-
brog. From the first generation of 1895, the progeny of the succeeding
year were found to be as follows :

Dominating (Mephisto) 24%

Hybrids (with 25% Danebrog) 51%
Recessive (Danebrog) 25%" {ib., p. 87.)

De Vries states {ib.^ p. 88.) :

"This result corresponds to the above assumed formula. Or, more cor-
rectly, out of these figures I first derived the formula.

"The dominating and the recessive characters show themselves accord-
ingly constant in the progeny, as far as they were isolated through
segregation. The hybrids, however, split again according to the same law.
Thty furnished, in this experiment, on the average, 77% with the domi-
nating, and 23% with the recessive character.

"This behavior remains, in the course of the years, the same. I have
continued this experiment through two still further generations. The
50% hybrids split ; the 25% dominating remain constant." {ib., p. 88.)

De Vries also confirms the principle that the hybrid, crossed
with either of the two parents, gives the progeny which, for the
character in question, are 50 per cent : 50 per cent. The cases are :

% Year
Clarkia pulchella X white 50 1896

Oenothera lamarkiana X brevistylis 55 1895

Silene armeria {red) X white 50 1895

Crosses were also made (1897), between the prickly Datura
tatula and the smooth D. stramonium inermis. The plants of the
first generation were blue with prickly fruits, as follows :

Flowers %

blue (dom. -f- hybrid) 72

white (recessive) 28

Fruits %

Smooth blue 26.8

Smooth white 28.0

Av. 27.4 {ib., p. 89.)

Expt

red.

3 leaflets

white,

5 "

red.

5 "

white,

3 "

PLANT HYBRIDIZATION BEFORE MENDEL 331

A cross was made between Trifolium pratense album and T.
pratense quinquefolium^ with the following results :

Calc.

These were for about 220 plants.

De Vries closes with the important statement (p. 89) :

"It is frequently possible, through the segregation experiments, to sepa-
rate simple characters into several factors. Thus, the color of flowers is
frequently composite and, after crossing, one obtains the individual fac-
tors, in part separated, in part in different mixtures."

Experiments with Antirrhinum majus, Silene armeria, and
Prunella vulgaris^ are stated as confirming the above.
De Vries' final statement is {ib., p. 90) :

"From these, and numerous further experiments, I conclude that the
law of segregation (Spaltungsgesetz), found by Mendel for peas, finds a
very general application, and that, for the study of the units out of
which the species-character is composed, it has a quite fundamental sig-
nificance." {lb., p. 90.)

One of the most striking features of the above paper is the
anticipation by De Vries of the multiple factor explanation for
certain characters such as flower color, first reported upon ex-
perimentally by Bateson for the crossing of two white sweet peas
of the Emily Henderson variety, which gave purple in the F^.

The next paper in the series to be considered is the third paper
of De Vries on "Erbungleiche Kreuzungen (Vorlaufige Mitthei-
lung)," constituting No. 53, in the Ber. d. d. Bot. Gesell., Novem-
ber 21, 1900. (ic.)

De Vries in this article, briefly begins by summarizing the
Mendelian discovery.

"In a paper published in these 'Berichte' concerning the Law of Segre-
gation of hybrids, I have shown that this law which Mendel had de-
rived from his investigations with peas, finds a very general application
in the plant kingdom, and is of capital importance for the theory of
hybridization. The since published important extensive investigations of
Correns, Tschermak, Webber and others, have established in part the
correctness of Mendel's results [Erfahrungen], and in part the justifica-
tion of this generalization.

"Mendel had demonstrated for his peas-crosses, that their results could
be derived in simple manner from certain principles. In the first place

332 PLANT HYBRIDIZATION BEFORE MENDEL

he found that, in the vegetative development of the hybrid individuals,
the one character of every character-pair is dominant (dominierend),
and the other recessive. On the formation of the sex organs, however,
the antagonistic characters, united in the hybrid, separate in such man-
ner that, in respect to each individual pair, the egg cells and pollen
grains are no longer hybrids. This splitting occurs in equal parts, in
that 50% of the sexual cells contain the one, and 50% the other char-
^acter of each pkir. In respect to this splitting, the two antagonistic char-
acters are of equal value, independently of the question as to whether
they are dominating or recessive in the vegetative life." (ic, pp. 435-6.)

The remainder of the paper is a discussion of an apparent ex-
ception to the law of equal splitting, as demonstrated by certain
Oenothera crosses.

This concludes the contributions of De Vries to the Mendelian
discovery.

It would not do full justice to the work of De Vries in this
connection, if adequate cognizance were not taken of his point
of view in certain fundamental matters bearing upon the unit-
factor hypothesis, already propounded in his "Intracellular
Pangenesis," originally published in German in 1889. (le.) The
following extracts are taken from the English translation of 1910
(id), which renders the original without revision. (Italics, where
used, are inserted throughout.)

Referring to the nature of specific characters, De Vries says :

"But, if the specific characters are regarded in the light of the theory
of descent, it soon becomes evident that they are composed of single
factors more or less independent of each other. One finds abnost every
one of these factors in numerous species, and their varying groupings
and combinations with less common factors cause the extraordinary diver-
sity in the organic world.

"Even the most cursory comparison of the various organisms leads, in
this light, to the conviction of the composite nature of specific charac-
ters." (ed. 1910, p. II ; ed. 1889, p. 8.)

Again, "the variation of the individual hereditary characters
independently of one another" ["Das Variiren der einzelnen erb-
lichen Eigenschaften unabhangig von einander"] (ed. 1910, p.
19; ed. 1889, p. 16), constituted the subject of a not inconsider-
able discussion, in which it is stated :

"A comparative consideration of the organic world convinces us that
the hereditary characters of a species, even if connected with one another
in various ways, are yet essentially independent entities, from the union
of which the specific characters originate."

PLANT HYBRIDIZATION BEFORE MENDEL 333

The fact is emphasized that, in both the plant and the animal
kingdoms :

"The independent varying of single characteristics forms the rule,
while the combined variation of them is the exception." (ed. 1910, p. 21 ;
1889, p. 17.)

De Vries then asserts, in a significant and for the time rather

remarkable sentence, that :

"In most cases it cannot be decided whether the germ attribute is de-
termined by a single hereditary character or by a small group of them."

The section closes with a significant comment upon one phe-
nomenon, which, he says,

"greatly complicates the study of hereditary characters," viz., the fact
"of their being commonly united in smaller or larger groups which be-
have like units, the single members of the groups usually appearing
together."

De Vries remarks upon the fact that different authors, such as

Darwin and Nageli, have also strongly emphasized this point, but,

he adds, the working-out of the theory in detail is rendered diflfi-

cult by the fact that :

"In many cases it will obviously be extremely difficult to decide
whether one is dealing with a single hereditary character, or with a small
group of them." (ed. 1810, pp. 23-4; ed. 1889, pp. 21-2.)

It will be especially interesting to quote rather fully from the
discussion on the matter of unit-characters in hybrids :

"In summarizing briefly what has been said, we see that experiments
and observations on the origin and fixing of variations teach us to
recognize hereditary characters as units with which we can experiment.
They teach us further that these units are miscible in almost every pro-
portion, most experiments really amounting merely to a change in this
proportion." (ed. 1910, p. 27; ed. 1889, p. 24.)

"The above considerations are verified in a striking manner by experi-
ments in hybridization and crossing. In no other connection does the
conception of a species as a unit made up of independent factors stand
forth so clearly. Everyone knows that the hereditary character of two
parents may be mixed in a hybrid. And the excellent experiments of
man3^ investigators have taught us how, in the descendants of hybrids,
an almost endless variation can be observed, which is essentially due to
a mixing of the characteristics of the parents in a most varied manner."
(ed. 1900, p. 27; ed. 1889, p. 25.)

"The hybrids of the first generation have quite definite characteristics
for each pair of species. If one produces a hybrid of two species, which
previous investigators have already succeeded in crossing, he can, as a
rule, rely on the description given of it tallying exactly with the newly
produced intermediate form, if the hybrid is fertile without the help
of its parents, and if its progeny are grown through a few generations

luj(LliRA»^Y]^

334 PLANT HYBRIDIZATION BEFORE MENDEL

in thousands of specimens, one can almost always observe that hardly
any two are alike. Some revert to the form of the pollen-parent, others
to that of the pistil-parent, a third group occupies a central position.
Between these are placed the others, in the most motley variety of
staminate and pistillate characteristics and in almost every graduation of
mutual intermixture." (ed. 1910, p. 27; ed. 1889, p. 25.)

"Many and prominent authors have pointed out the significance of
hybrids for establishing the nature of fertilization. With the same right,
we may use them in trying to penetrate into the mystery of specific char-
acter. And then they clearly prove to us that this character is fundamen-
tally not an indivisible entity. The characteristics of a hybrid {of the
first generation) are as sharply defined and as constant, and on the whole
of the same order, as those of the pure species, and the frequent specific
name, 'hybridus,' might go to prove that even the best systematists felt
this agreement." (ed. 1910, p. 28; ed. 1889, p. 26.)

De Vries remarks, with considerable acumen, that the combina-
tion in a hybrid, of two, three, or more species, is not in itself a
matter of importance. The species entity concept was discarded
by him for the unit-character concept, already as early as 1889.
There is no reason other than a purely practical one, why any
limit need be put to the number of species entering into the hy-
brid composition ; why,

". . . in fact, there should not be combined in one hybrid character-
istics which have been taken from an unlimited series of allied species.
But this is of small importance, the chief point being the proposition that
the character of a pure species, like that of hybrids is of a compound
nature." (ed. 1910, pp. 27-8; ed. 1889, pp. 24-6.)

Further on he says :

"The process of fertilization, In Its essence, does not consist therefore
in the union of two sexes, but In the mixing of the hereditary characters
of two individuals of different origin, or at least such as have been sub-
jected to different external conditions." (ed. 1910, p. 31 ; ed. 1889, p. 29.)

Further comment on the subject of the existence of hereditary

characters as factorial units or unit factors Is as follows:

"Let us regard the individual hereditary factors as independent units,
which can be combined with each other in different proportions into the
individual character of a plant." (ed. 1910, p. 31 ; ed. 1889, p. 29.)

"In the preceding paragraphs we have seen how the single hereditary
characters occur as independent units in the experiments of hybridization
and crossing, and how they can be attained in almost every degree. In
the same way evidently, we miist think of those units as independent in
the ordinary process of fertilization as well." (ed. 1910, p. 33; ed. 1889,

p. 31-)

"Seemingly elementary, the specific character Is actually an exceed-
ingly complex whole. It is built up of numerous individual factors, the
hereditary characters. The more highly differentiated the species, the
higher is the number of the component units. By far the most of these

PLANT HYBRIDIZATION BEFORE MENDEL 335

units recur in numerous, many of them in numberless, organisms, and
in allied species the common part of the character is built up of the
same units." (ed, 1910, p. 33; ed. 1889, pp. 31-2.)

The following statement is, perhaps, especially important as

indicating De Vries' attitude at a period considerably antecedent

to his experimental investigations upon unit-factors of the Men-

delian type :

"The hereditary factors, of which the hereditary characters are the
visible signs, are independent units which may have originated sepa-
rately as to time, and can also be lost independently of one another.''
(ed. 1910, pp. 33-4; ed. 1889, pp. 31-2.)

The fact is called attention to that, although the factors are

independent to such a degree that each may of itself become

weaker and even disappear completely, yet they are, as a rule,

united into smaller or larger groups, in which they act at least

in co-ordinate fashion, so that :

"when external influences, such as a stimulus to gall-formation, bring
a definite character into dominance, the entire group to which it belongs
is usually set into increased activity." (ed. 1910, p. 34; ed. 1889, p. 32.)

b. Correns, C.

Regarding his discovery of Mendel's paper, and the inception
of his work with Pisum^ Professor Correns reports as follows ;
(letter of January 23, 1925) :

"You ask further concerning the re-discovery of the Mendelian Laws.
I cannot add much to what I have contributed in the Mendel issue of
the 'Naturwissenschaften.' It will, in the meantime, certainly have reached
your hands. The operation of a principle was soon 'found in the case
of peas and maize. I was able accordingly soon to proceed systematically
in the experiments, as the two genealogies for peas in my first con-
tribution show. I did not come at first upon the explanation of the
regular relationship [Gesetzmassigkeit], but I likewise, however, did
not seek intensively after it. For I wished, for various reasons, to first
finish an extensive book upon the sexual propagation of the foliose
mosses, upon which I had worked for years. I then wished first to push
intensively the elaboration of the investigations on xenias and hybrids,
which had been carried on at the same time since 1894. The printing
of the book lasted until in August 1899; then I was able to devote
myself earnestly to the genetics researches. The date of the day upon
which, in the autumn (October) of 1899, I found the explanation, I no
longer know ; I do not make note of such matters. I only know that it
came to me at once 'like a flash,' as I lay toward morning awake in bed,
and let the results again run through my head. Even as little do I
know now the date upon which I read Mendel's memoir for the first time ;
it was at all events a few weeks later. I then first made ready for the
piress the contribution on xenias in maize. In it, it is already pointed

Plate XLV. Professor C. Ccrrens, Director, Kaiser-Wilhelm Institut fiir Biologic, Berlin.

PLANT HYBRIDIZATION BEFORE MENDEL 337

out, that in crosses between maize races I had found very interesting but
very complicated relationships. That other investigators also worked in
the same direction I naturally did not know, otherwise I would have
hastened more with the preparation of the publication.

"On the morning of the 21st of April, 1900, I received a separate 'Sur
la loi de disjonction des hybrides,' of De Vries, and by the evening of
the 22nd of April, my contribution, 'G. Mendels Regel iiber das Ver-
halten der Nachkommenschaft der Bastarde,' was ready. I sent it to the
German Botanical Society in Berlin, where it was received April 24, and
was reported in the session of April 27. The issue in question of the
'Berichte' appeared at the end of May, about the 25th. The contribution
has been again printed in the volume in which the German Society for
the Science of Heredity has recently collected my genetic works, insofar
as they have not appeared independently anew.

"For that matter, I do not lay too much weight upon the re-discovery
itself. According to my opinion, it was important that the Mendelian
laws should finally be known and verified. Whether it happened by their
being independently found anew, or through the fact that someone first
read the memoir of Mendel, and then repeated the experiments, is, how-
ever, at bottom, an indifferent matter for science. It was accordingly only
a confirmation of what had been discovered more than 30 years before.
And through all that in the meantime had been discovered and thought
(I think above all of Weismann), the intellectual labor of finding out
the laws anew for oneself was so lightened, that it stands far behind the
work of Mendel. I myself should prefer, for my part, to lay more weight
upon my later works, e.g., the Bryonia experiments."

In response to further inquiry, Professor Correns' reply is as
follows (letter of January 30, 1925) :

"I did not discover the constant relationship [Gesetzmassigkeit] in
Pisum alone but in Zea and Pisum simultaneously. In the publication, I
placed Pisum in the foreground on Mendel's account, and out of didactic
considerations. That I, however, also experimented with Pisum almost
from the beginning, is explained from the way in which, as a matter of
fact, I arrived at my genetic investigations. Originally I started out to
solve the xenia question. To this end I wished to test experimentally all
the assertions known in the literature. I began (1894) with Phaseolus
vulgaris nanus (with which, however, cross-fertilization did not succeed
at all for me), then with Zea, Pisum, Lilium and Matthiola. This is all
related in my 'Crosses between maize races, with particular reference to
xenias,' Bibliotheca Botanica, Heft 53 (1902), where the results are also
mentioned ; those upon Matthiola were also published previously in an-
other place. For Pisum there are different pertinent assumptions. One
only needs refer, for example, to Darwin, 'The variation of animals and
plants under domestication,' and to Focke. Unfortunately Focke here,
in the case of xenias, does not mention Mendel, otherwise I should
have probably read his work immediately at the beginning of my in-
vestigations. After I had carried on cross-fertilizations with Pisum like-
wise on account of the xenia question (there exist, indeed, assumptions
on the influence of the seed-coat), it was I suppose, quite natural to
grow the crosses themselves, as I did not only with Pisum, but also

338 PLANT HYBRIDIZATION BEFORE MENDEL

with Zea and Matthiola, and finally also with Lilium. In this connection
the advantages of Pisum naturally made themselves at once noticeable,
especially the great convenience of the investigations, which, indeed, 1
could only carry on accessorily.

"To one of my most fruitful objects of research, Mirabilis jalapa,
I also first came indirectly, when I investigated (1907) the influence
which the; number of pollen grains used for pollination has upon the
progeny. I had originally, indeed, not at all overlooked the matter of
studying the behavior of the progeny in further generations, but had
proceeded from other bases of inquiry.

"Besides through Focke's book, I had been made cognizant of Mendel's
investigations through my teacher Nageli. And I believe also to remem-
ber that he told me of Mendel, but certainly only of the Hieracium
investigations, in which alone he was permanently interested. Some-
thing of them was known to me also from the theoretical introduction
to the first volume of the Hieracium monograph of Nageli and Peter,
and from Nageli's introduction to the Primula monograph of E. Widmer.
The memoir of Mendel on his Hieracium hybrids I first read, however,
• with that on the peas hybrids, in the autumn of 1899. Nageli was, at
the time when I became his pupil, already in ill health, read none of
his colleagues' works any longer, and likewise no longer conducted his
practicum any more. He interested me in the structure and growth of
the vegetable cell membrane. When I began the genetic researches (1891),
he was already dead. The above-cited references to Mendel, and indeed
also the recollection of the verbal mention of Mendel, prompted me
to ask Nageli's family for possible letters received. His scientific corre-
spondence was, however, not to be found at that time. It first came to
light through an accident in 1904. The letters of Mendel were sent to
me by the family, and were published by me ; the remaining scientific
correspondence the family then destroyed."

In Die Naturwissenschaften, lOth Jahrgang, Heft 29, pp.
623-31 (July 21, 1922), a number devoted to papers in memory
of Gregor Mendel, on the one hundredth anniversary of his
birth, Professor Correns contributed an article entitled, "Etwas
iiber Gregor Mendels Leben und Wirken." In the course of this
article (p. 630), Correns reports as follows. His comments are
herewith introduced as supplementary to the letters quoted above :

"Through experiments in xenia formation, I have had my attention
directed to the behavior of hybrids in maize and peas races. The in-
vestigations, however, could only be carried on slowly, in a certain de-
gree as side issues, through years, together with the other work, so that
I was already able to propound, in the first contribution on Pisum
sativum, a genealogical tree up to the fourth generation inclusive. I had
soon come to the counting-out stage, and also to the correct explanation,
when for the first time I looked through the literature, and found that
my results were not new. Focke says on the subject of Pisum in his
'Pflanzenmischlinge' (1881) that Mendel's numerous peas crosses gave

PLANT HYBRIDIZATION BEFORE MENDEL 339

results which were quite like those of Knight, 'but Mendel believed
that he found constant numerical relationships between the types of the
hybrids.'

"It has occurred no differently with De Vries and von Tschermak.
De Vries especially, in the lecture given on July 11, 1899, at the first
'Hybrid Conference in London,' on 'Hybridizing of Monstrosities,' and
which first appeared in April 1900 (Journ. Roy. Hort. Soc. 24:69), de-
scribed, although quite without the precise Mendelian formulation, the
hybrid between the smooth Melandrium album glabrum (M. preslii Opiz)
and the typically hairy race of Melandrium rubrum, which, with respect
to the hairiness, typically Mendelizes."

Following is the paper of Correns entitled, "G. Mendels Regel
iiber das V^erhalten der Nachkommenschaft der Rassenbastarde,"
Ber. d. d. bot. Ges. Vol. 18, published April 24, 1900 (2a).

The paper opens as follows :

"The latest publication of Hugo De Vries, 'Sur la loi de disjonction
des hybrides' [Comptes Rendus de L'Acad. des Sci., Paris, March 26,
1900], which I came into possession of yesterday, through the generosity
of the author, prompts me to the following contribution :

"l also, in my hybridization experiments with races of maize and peas,
had arrived at the same result as De Vries, who experimented with
races of very different sorts of plants, among them also with two maize
races. When I had found the orderly behavior, and the explanation there-
for— to which I shall immediately return — it happened in my case, as it
manifestly now does with De Vries, that I held it all as being something
new. / then, however, was obliged to convince rnyself that the Abbot
Gregor Mendel in Briinn in the 6o'j, through long years of and very
extended experiments with peas, not only had come to the same result
as De Vries and I, but that he had also exactly the same explanation, so
far as it was at all possible in 1866." (2a, p. 1 ?8.)

". . . The work of Mendel's, which is indeed mentioned in Focke's
'Pflanzenmischlinge,' but has not been adequately appreciated, and which
has otherwise scarcely found attention, belongs to the best that has been
ever written upon hybrids, in spite of numerous demonstrations which
no one can make in incidental matters, for example, in what pertains to
their terminology.

"I have then not held it to be necessary to assure myself the priority
for this 'post-discovery,' through a preliminary contribution, but de-
cided to continue the experiments still further. I confine myself in the
following to a few statements concerning the results with races of peas."
{ib., p. 159.)

"The races of peas are, as Mendel correctly emphasizes, precisely in-
valuable for the questions interesting us here, because the flowers are
not only autogamous, but also are exceedingly seldom crossed by in-
sects. I came upon these circumstances through my experiments on the
formation of xenias — which here gave only negative results — and fol-
lowed the observations further, when I found that here the 'regularity'
is much more evident than with maize, in which it had first come to
hand with me.

340 PLANT HYBRIDIZATION BEFORE MENDEL

"The characters through which the races of peas are distinguished,
one can, as generally, arrange together in pairs, in which every member
of a pair relates to the same point, the one with the one, the other with
the other race, e.g., to the color of the cotyledons, of the flower, of the
seed-coat, of the hilum on the seeds, etc. In many pairs, the one char-
acter, or as the case may be the primordium [Anlage] of it, is so much
'stronger' than the other, or e.g., the primordium, that only it alone
comes to light in the hybrid plant, while the other throughout does not
show. One can call the one the dominating and the other the recessive,
as Mendel did in his time and, through a remarkable accident, De Vries
does also now. Dominating, is, for example, the yellow color of the
cotyledons as opposed to green, the red of the flower as opposed to
white.'' (p. 159.)

"It is, however, quite incomprehensible to me, as De Vries is able to
assume, that in all character-pairs in which the two races differ there
is one dominating pair-member in the hybrid." [The author here quotes
from De Vries, as follows: Comptes Rendus, 1900, p. 845: "Per contra,
the study of the simple characters of hybrids is able to furnish the
most direct proof of the principle enunciated — the hybrid shows always
the character of one of the two parents, and that always in all its force;
never is the character of the parent, which is lacking to the other one,
found reduced by half."]

"Even in the races of peas, in which several character-pairs correspond
exactly to the scheme, there are others in which no character dominates ;
thus the color of the seed-coat, whether red-orange, or greenish-hyaline.
Then again, the hybrid can show all transitions, even in the seed-coat
of peas, or it shows always more of one than of another character, as
Stocks hybrids, in which, for example, a given hybrid can still be dis-
tinguished from the one parental race by the markedly weaker pubes-
cence, but always, after some examination ; while with the other, the
smooth parental race, it extraordinarily contrasts." (p. 160.)

For some two pages and a half, Correns then outlines Men-
del's general results with a single pair of allelomorphs, and fol-
lows with a tabular statement of his individual results.

Experiment I

Cross between late Erfurt green "Folgeerbse" with green cotyle-
dons, and "purple-violet" (Schlesien) "Kneifelerbse," with yellow
cotyledons.

Generations

Fi 51 yellow (19 planted)

Fo 619 yellow (25 planted) 260 green (25%) (11 planted)

7 yellow (28%)

251 yellow 550 yellow 195 green (26.2%) 538 green

(7 planted) (18 planted) (14 planted) (10 planted)

PLANT HYBRIDIZATION BEFORE MENDEL 341

F4:

224 yellow 216 yellow 225 yellow 70 green 307 green

(23-89%)
Experiment II

Late green Erfurt "Folgeerbse" with green cotyledons, and
"Bohnenerbse" with yellow cotyledons.

Fi 31 yellow (12 planted)

775 yellow 247 green

(21 planted) (20 planted)

292 green 462 yellow 149 green 670 green

(23.6%)

Correns holds (p. 164) that the separation of dominant and
recessive factors (Anlagen) takes place at the earliest, on the
laying down of the primordia of the ovules and stamens, and at
the latest, on the first nuclear division in the pollen grain, and in
the division at which the primary embryo-sac nucleus is formed.

As to the fact that, when the hybrid in the Fj^ generation, in-
stead of being self-pollinated, is pollinated with pollen from the
dominant parent, its progeny is half dominant pure, and half
dominant, but giving progeny 3: 1 dominant and recessive; and
that when an F^^ hybrid is pollinated by the recessive parent, it
gives a progeny one half of which is recessive, the other half
dominant, but producing progeny 3 : 1 dominant and recessive ;
Correns states (p. 165) :

"This theoretically derived rule I find realized in my maize crosses."

Correns shows in this first paper a full insight into the signifi-
cance of the following rule of Mendel :

"it is thereby proven at the time, that the behavior of every two differ-
ing characters in hybrid combination is independent of the differences
otherwise in the two parent plants,"

by the statement in a note (p. 166) that,

"Even this rule does not hold in general; there are races with coupled
characters."

This is, for the time, knowledge in advance of the then state
of investigation with respect to Mendelian behavior.

Moreover the later work of Bateson on hybrids of sweet peas,
involving pollen grains of different shapes, is already forecast
by Correns in the statement (footnote, pp. 166-7) •

342 PLANT HYBRIDIZATION BEFORE MENDEL

"if the pollen grains differ externally in the parent races, then one may
expect that the hybrid may form two kinds of pollen cells, externally
distinguishable among themselves, in case Mendel's rule holds good. This
is in fact true, as Focke first observed."

Correns appears to have been the Hrst to comprehend so thor-
oughly the fundamental nature of the Mendel experiments, as to
give the general result the designation of "Mendel's Law."

"The hybrid forms sexual nuclei which unite with the primordia [An-
lagen] for the individual characters of the parents in all possible com-
binations, but not those of the same pair of characters. Every combination
appears about equally often.

"if the parent races differ only in one pair of characters (two charac-
ters, Aa), then the hybrid forms two kinds of sexual nuclei (A,a), which
are like those of the parents ; of each sort, 50% of the total number, if
they differ in two pairs of characters (four characters, Aa, Bb), then
there are four kinds of sexual nuclei (AB, Ab, aB, ab) ; of each sort
25% of the total number, if they differ in three pairs of characters (six
characters, Aa, Bb, Cc), then there exist eight kinds of sexual nuclei
(ABC, ABc, Abe, Abe, aBC, aBc, abC, abc) ; of each sort 12.5% of the
total number; etc." (p. 166.)

Immediately following this illustration, the statement is made :

"I call this the Mendelian Rule : it includes also De Vries' 'Loi de dis-
jonction.' Everything further may be derived from it." (p. 167.)

We thus have here the first completely definite analysis of the
Mendelian paper itself, of Mendel's own results, and the first
use of the term, "The Mendelian Rule" or "Law."

However, Correns was not at the time at all of the opinion
that Mendel's Law was a universal one in its character. He held
that it obtained for a certain number of cases, and presumably
for those where a single member of the character-pair dominates,
and for the most part only in the case of race- or variety-hybrids.

Correns holds that the view :

"That all parts of hybrids follow it, is quite out of the question."

To this point he cites his cases of crosses between two races of
peas with colorless and with orange-red seed-coats becoming
brown on ripening, in which, in the first generation, different
stages of intermediates are found. In the second generation, the
extremes of yellow and colorless gave aga(n the same extremes,
united by a series of transition-stages. The same is stated to hold
for the character of the seeds, and their form and size. (p. 167.)

We thus have in this paper an analysis of the work of Mendel,

PLANT HYBRIDIZATION BEFORE MENDEL 343

and one which already itself constitutes a preliminary investiga-
tion into the more complete understanding of the supposed ex-
ceptions, which latter formed a few years later one of the main
fields of inquiry, until the functioning of several possible factors
or "genes," operating for the same single phenotypic "character,"
was more fully demonstrated. This was probably first achieved,
as already stated, by the work of Professor William Bateson for
sweet peas ("Reports to the Evolution Committee of the Royal
Society." Report II, pp. 88-90; "Experiments carried out by W.
Bateson, E. R. Saunders, and R. C. Punnett in 1904," pp. 80-99).
Regarding this matter, however. Professor Bateson writes as
follows (letter of Februar}^ 2, 1925) :

"l am not sure whether the color of the sweet peas should be regarded
as the first compound character demonstrated. Perhaps it should, but the
walnut comb and the hoariness of stocks were made out about the same
time.

c. E. von Tschermak.

Regarding his discovery of Mendel's paper, and his initial re-
search in relation thereto, Professor von Tschermak reports as
follows (letter of January 7, 1925) :

"After the taking of my doctorate at the University of Halle a. S.
(1895), ^t the instigation of my teachers Maercker and Riimker, I became
occupied for two years as volunteer in the horticultural business of the
firms Chr. Bertram, in Stendal (1896), and of Sachs, Dippe and Metter,
in Quedlinburg (1897). This sojourn, as well as a visit to the renowned
grain-breeding stations in the Province of Saxony, especially to Amtsrat
Dr. Rimpau in Schlanstedt, awakened my interest in practical questions.
My address ^ 'Concerning methods of improvement and breeding of agri-
cultural and horticultural plants in Germany' at the Club der Land-und-
Forstwirthe in Vienna, January 7, 1898, brought me into relations with
the '"Hochschule fiir Bodenkultur' in Vienna. Prof. Dr. A. Liebenberg
placed in prospect for me the assistant's place in his department, which,
however, at that time was not vacant. Following the suggestion of a
pupil of my father, the mineralogist. Professor Renard, at the University
of Ghent, to extend my practical horticultural knowledge among some
well-known horticultural enterprises of Belgium, Holland arid France,
I betook myself in the spring of 1898 to Ghent. The circumstance, that
I there found only the opportunity to get acquainted with hot-house
management, but not with the breeding of vegetables and garden flowers
as I expected, was the inducement to strive to apply the abundant time
remaining available to experimental work in the botanical garden, which
interested me so exceedingly that I devoted myself exclusively to my

1 wiener landwirtschaftliche Zeitung, 1898.

Plate XLVI. Professor E. von Tschermak, Landwirtschaftliche Hochschule, Vienna.

PLANT HYBRIDIZATION BEFORE MENDEL 345

investigational activity. Professor MacLeod, Director of the Botanical
Garden in Ghent, discussed quite briefly with me a program of work to
carry out pollination experiments with plants to be selected, which
should determine, whether perchance, in individual cases, with respect
to development of the fruit, differences existed as the result of auto-
gamous, geitonogamous and xenogamous fertilization of like or dis-
similar species. I had in the beginning the good fortune, quite by chance,
to choose for these investigations the Wallflowers, in which xenogamy
increased the growth in length of the shoot by about twofold, as com*
pared with autogamy and geitonogamy. These experiments were later
continued and extended in Vienna.^ since I remained in Ghent only until
July, it was a question of looking out for a plant which could bring its
vegetation-period to a close by this time. I selected peas, impelled by the
reading of Darwin on the effects of cross- and self-fertilization. I was
also urged by the incompleteness of the observation-material in the case
of this plant with Darwin (only four pairs of plants were measured and
compared to complete these experiments). The yield-results from my ex-
periments I took with me to Vienna. From these, together with other
questions to be answered, since green-cotyledonous peas had been crossed
with yellow-cotyledonous, wrinkled-seeded with round-seeded, I had
already been able to determine the method of operation of the xenia
effect, since the prospective assistant's position was still not yet ooen
in 1809, T volunteered for a year on the estate of the Imperial family's
foundation in Esslingen, near Vienna, because the setting apart of ^0
hectares from this management for the purpose of the founding of an
exoerimental establishment for our Hochschule was in prospect.

'■'There, in the garden of a neighboring estate owner, my experiments
with peas, begun in Ghent, were continued, and at the same time, new
crosses Instituted with grain and garden beans. The working ud of the
F-. of my peas hvbrids, followed in the fall of 1899. In this I was
struck especially by the different value of the characters of the indi-
vidual races with resnect to their structure, cotyledon-color and form
('see conclusion III of my first paper, in which I emphasized besides
th^t. Instead of 'domlnleren' fdomlnatel, one should say rather *ptS-
valleren' [predominate], at least In certain cases [see conclusion VIll).
In counting out the seed-characters, the ever-recurring number relation-
ship of 3:1 could naturally not escape me, any more than the number-
relation of 1:1 on back-crossing of green-seeded peas with hybrid pollen
of the F, generation. The rules of inheritance, quite Intentionally, I ex-
pressed at first purely descriptively or phenomenologically. In order not
at once to anchor the newly-beginning experimental phase of the doctrine
of heredity — as had happened Inexpediently with Darwinism — to definite
theoretical terms. From this standpoint, I designated the regularities
found by Mendel and myself, as those of the regularly varying values
of the characters for the inheritance, under which I comprehended not
only the rule of dominance, but mass-value (domlnance-recessiveness, or
equivalence of value) ; quantities-value (the relation of segregation),
and Inheritance-value, or splitting per se.

"Later likewise, I have remained consistently faithful to that stand-

2 Beihef te der deutschen botanlschen Gesellschaft, 1902, Heft 1.

346 PLANT HYBRIDIZATION BEFORE MENDEL

point which separates the permanent good of the exact facts of observa-
tion clearly and distinctly from the naturally and necessarily changing
expression of theoretical explanations, especially of fertile working
hypotheses.

"In the autumn of 1899, I received from Prof. A. v. Liebenberg the
permission to volunteer in his department, and to make use of the library.
The first work I seized upon was the well-known book of Focke : 'Pflan-
zenmischlinge,' of 1881. There I found, in the chapter on 'Peas,' the
familiar obscure expression of Focke's concerning Mendel's treatise, as
well as the views on Mendel's experiments with beans and Hieraceae.
since Mendel's work was not on hand in the library of the Hochschule
fiir Bodenkultur, I had on the same day of this 'discovery' the 'Transac-
tions of the Natural History Society of Briinn,' hunted out of the Uni-
versity library, which now gave me the information, to my greatest sur-
prise, that the regular relationships discovered by me, had already been
discovered by Mendel much earlier. Still, I believed myself to be at this
time the only one who had made this discovery anew. By Christmas, my
paper was finished, ready for publication, and on the 17th of January,
1900, it was delivered at the rectorate of the Hochschule fiir Boden-
kultur, as an inaugural dissertation. In the beginning of April 1900, I
received from Hugo De Vries, whom I had visited from Ghent in the
year 1898, the article 'Sur la loi de disjonction des hj^brides' (March 26,
1900), in which De Vries, on pages 1-2 says: 'in the hybrid the simple
differential character of one of the parents is then visible or dominant,
while the antagonistic character is in the latent or recessive state.' I read
this sentence with the greatest interest, but also, frankly stated, with
consternation, for it was now quite clear to me that De Vries must also
know the work of Mendel, although it was not cited in this paper. For
me it was naturally, as a beginning docent, not indifferent that my work
should be anticipated, wherefore I immediately sought from the rectorate
the permission to let my already censored Avork be taken out and printed.

"l have my friend Dr. Bersch to thank that my work was accepted
for the Zeitschrift fiir das landwirtschaftliche Versuchswesen in Oester-
reich, and the printing of it immediately undertaken. In the meantime
there appeared soon thereafter the extensive work of De Vries in the
Reports of the German Botanical Society (Heft 3). I was able to utilize
it already as early as during the correction of my proofs. On the reading
of the second proof I was surprised anew by the work of Correns (Ber.
d. d. Bot. Gesell. Heft 4, April 24). I was therefore able to take it into
consideration only in the footnote to my first paper. As may readily be
conceived, I now made every effort to induce the publisher of the journal
before-mentioned, as well as the printing office, to publish the separates
of my work before the appearance of the number in question, which,
fortunately, likewise succeeded (May, 1900). In the meantime, I wrote
quickly an abstract of my paper, for the Berichte der deutschen botan-
ischen Gesellschaft (received for publication June 2, Heft 6), which,
however, appeared somewhat later than the separates of my complete
paper, which I immediately sent out.

"The classical significance of the Mendel work was at once clear to
me, for which reason, already in the year 1900, I made application for
its acceptance in Ostwald's 'Klassiker der exakten Wissenschaften,' pro-
vided with notes of my own. They delayed, however, so long with the

PLANT HYBRIDIZATION BEFORE MENDEL 347

printing, that I very impatiently wrote to the editor, that in the mean-
while the works of Mendel had been printed by Goebel in Flora (1901).
Now at length Mendel's works were found worthy of being enrolled in
the 'Klassiker der exakten Wissenschaften.' "

For the younger Tschermak, as he states, it was not easily
effected to bring his re-discovery of Mendel, simultaneously made
with De Vries and Correns, into general recognition. Thus, in
the early years after the re-discovery of the Mendel ian Laws, in
references to the discoveries the mention of his name was omitted
altogether, as in the "Lehrbuch" of Strasburger and Wettstein.
Nevertheless, this oversight was soon made good. Continuing, he
states :

"The practical significance of Mendelism for plant and animal breed-
ing was first immediately recognized by myself, and always emphasized ;
as also the great part of my publications even today, with theoretical
conclusions, always place the practical side in the foreground. Through
my visit in the year 1901 at Svalof, the method of breeding hitherto
obtaining there was directed to quite new, modern, 'Mendelian' lines,
which is now recognized ungrudgingly in Sweden by Nilsson-Ehle."

The preliminary paper of von Tschermak's, referred to in the
letter above, contributed to the Berichte der deutschen botanischen
Gesellschaft, and entitled "tJber kiinstliche Kreuzung bei Pisum
sativum^'' was printed as Contribution 26, pp. 232-9 of volume
18, and received by that journal for publication on June 2, 1900.
This paper, although in a sense an abstract of the much fuller con-
tribution to the Zeitschrift fiir das landwirtschaftliche Versuchs-
wesen in Oesterreich, Heft 5, 19CO, is nevertheless of special in-
terest, since it renders the first account of the author's experi-
ments appearing in the issues of a botanical journal.

The author states :

"Prompted by the experiments of Darwin on the effects of cross- and
self-fertilization in the plant kingdom, I began in the year 1898 to
institute crossing experiments with Pisum sativum, because especially
the cases of exceptions from the principle generally expressed, concern-
ing the advantageous effect of the crossing of different individuals and
different varieties in contrast to self-fertilization, interested me — a group
to which Pisum sativuvi also belongs." (3a, p. 232.)

The author then gives a brief summary of Darwin's experi-
ments, and states that, in view of the small amount of the lat-
ter's experimental material, it appeared to be called for, espe-
cially since Darwin did not emasculate the flowers, to repeat these

348 PLANT HYBRIDIZATION BEFORE MENDEL

experiments on a larger scale and with greater exactness. (zT?.,
p. 232.)

The central point of the paper, so far as the Mendelian dis-
cussion is concerned, follows :

"l also carried out artificial crosses between different varieties of
Pisum sativum, which had as the objective the study of the immediate
influence of the foreign pollen upon the constitution (form and color)
of the seeds produced thereby, as well as to follow in the following
generations of the hybrids the inheritance of constant differing charac-
ters of the two parent sorts used for crossing.

"In the second year of the experiment, the behavior of the hybrids
in respect to their growth (especially with respect to their height), their
seed-production, and the change in color and form of the seeds and
pods, when placed in comparison with the corresponding characters of
the descendants obtained from self-fertilizati(;n of the parents." (ib.,

P- 233.) ....

"On nine different varieties of peas, crosses were carried out between

flowers of the same plant (geitonogamy), between flowers of the same
variety but of other individuals (isomorphic xenogamy), and between
flowers of different varieties, the seeds of which are distinguished from
one another either through their form, or color, or through both char-
acters (heteromorphic xenogamy)." (pp. 233-4.)

The results of the experimental work then briefly follow (ib.,
pp. 234-9) ■

The crossing-for-height experiment contirmed Darwin's results,
so far as the comparison of self-fertilized plants with geitonoga-
mous crosses was concerned. With respect, however, to crosses in
the ordinary sense (heteromorphic xenogamy), i.e., those between
varieties called by the author "Mischlinge" (hybrids), only cer-
tain of the hybrid forms showed Increased growth in height over
the selfed plants.

"with other combinations, on the other hand, such an 'advantage' of
crossing as against self-fertilization was lacking, and a plus increment
of the hybrid as compared with the self-fertilized maternal variety, for
example in the case of a hybrid from a relatively dwarf variety, with a
relatively tall one, is primarily indeed simply to be taken as an inheri-
tance from the father, and is not to signify an 'advantage' from crossing
per se in contrast to self-fertilizaticm.

"For an interpretation in the latter sense, only such cases are justifi-
able in which the hybrid exceeds in height the derivations of self-
fertilization not only of the maternal variety, but also of the paternal
one." (ib., p. 234.)

There follows hereupon the statement of the significant results
of von Tschermak's own experiments, so far as F^ dominance is
concerned :

PLANT HYBRIDIZATION BEFORE MENDEL 349

"The taller type has always the greater influence, indifferently as to
whether it is due to the maternal or the paternal variety. The deriva-
tives of a relatively dwarf sort appear, after pollination with the pollen
of a relatively tall one, as Andrew Knight has already observed, rela-
tively strongly increased in height; in the reverse case, the hybrids, if
generally so, are yet only a little dwarfed." {ib., p. 234.)

The author's account follows of the results obtained in respect
to form and color inheritance in the seeds :

"In certain cases of artificial crossing of different varieties of peas, a
direct influence of the foreign pollen upon the seeds could be deter-
mined. Quite definite combinations led with regularity to this effect. The
characters, which were taken into consideration for the recognition of
such an influence, related to the form of the seeds, and the color of
the storage tissue. The seeds of the varieties used were either round, and
at the same time smooth or only slightly wrinkled, or they were more
or less cubical (Pismn quadratuyn), and at the same time deeply wrinkled.
The color of the storage tissues was either yellow, or green in many
shades. My experiments gave as a result that the selected differences in
the same structure, and hence the characteristic 'characters' of the indi-
vidual varieties, showed themselves in respect to their inheritance as not
of equal value. Regularly the. one character in question of the paternal
or maternal plant comes exclusively to development (dominating char-
acter according to Mendel), in contrast to the recessive character of the
other parent plant, which, however, in the seeds of the hybrid plants
is accustomed in part to come again to light. In harmony with the state-
ments of Mendel, the round, smooth form manifested itself as dominat-
ing, in contrast to the cubical, deeply wrinkled one ; the yellow colora-
tion of the storage tissue in contrast to the green color, and indifferently
indeed whether the seed- or the pollen-parent possessed this character
(as also Mendel)." (p. 235.)

Von Tschermak calls attention to a fact not mentioned in Men-
del's paper, that:

"The appearance of the dominating and the recessive character is not
a purely exclusive one. In individual cases I was able further to deter-
mine with certainty a simultaneous appearance of both, that is to say, of
transition stages. The principle founded by the investigator named of the
regular inequality cf the characters for the inheritance, receives full
confirmation through my experiments with Pisum sativum, as well as
through the observations of Kornicke, Correns, and De Vries upon Zea
mays, and further by De Vries in his species crosses, and shows itself to
be highly significant for the doctrine" of inheritance generally." {ih.,
P- 235-)

A fact of considerable interest, likewise not noted by Mendel,
is cited as follows :

"In certain cases of form and, in part, of color-difference of the parent
varieties, and of indicated character-fusion in the products, each of the
parent sorts showed relatively more influence upon the structure (espe-

350 PLANT HYBRIDIZATION BEFORE MENDEL

cially form) of the crossed product, when it furnished the ovary, than
when it furnished the pollen." (p. 236.)

The obtaining of a 3: l ratio in the F^ from his own results is
stated by von Tschermak as follows :

"In the seeds of the hybrids (in the first generation), obtained through
self-fertilization, the characters yellow and smooth showed themselves,
exactly as in the cross-pollinated seeds of the mother plant, as of higher
value or hereditary potency than the characters green and wrinkled.
While, however, in the artificial breeding of products of heteromorphic
xenogamy, the first named characters are almost without exception domi-
nating, while the latter, 'recessive,' only in individual cases come to light
pure or as admixture, the former characters in the seeds of the first
hybrid generation only in the majority of cases get into expression pure ;
in the minority, the recessive characters come out pure. In the first
case there thus exists an almost absolute dominance, in the second
mere superiority ['Pravalenz'] (in a certain relationship). Mixtures of
both character groups are here also seldom, but perhaps less seldom than
there. The number of the bearers of the dominating or. prevailing char-
acter, to that of the bearers of the recessive, is related about as 3:1. The
comparison of the derivatives from reciprocal crossing of different va-
rieties showed, analogously to the results given above for the products
of reciprocal pollination, that in certain experimental cases the egg cell
appears to be a more operative bearer of the dominating color-character,
than the pollen cell. But for the proposition of a statement in this regard
further investigations are needed. The combination of two dominating or
recessive characters in one parental form carries with it the same behavior
in the seed production of the hybrids, as the characters in question do
when isolated. An alteration in the value, such as an increase of the
dominance [Pravalenz], does not thereby enter in." {ib., p. 236.)

This closes the essentially Mendelian portion of the above
paper, "tJber kiinstliche Kreuzung bei Pisum sativum.'' The
Zeitschrift fiir das landwirtschaftliche Versuchswesen in Oester-
reich, III Jahrgang, 1900, pp. 465-555. (3b contains the complete
report, of which the article in the Ber. d. d. hot. Ges. 18:232-9
was a preliminary account.) The complete account follows:

The experiments in question were begun in the Botanical Gar-
den at Ghent in Belgium in the spring of 1898. Yon Tschermak
says (letter to the author of January 7, 1925) :

"The principal incentive to the experimental work lay in the results
of Darwin's experiments on 'The Effects of Cross and Self Fertilization
in the Vegetable Kingdom,' (1877). The experiments prove that seedlings
from a cross between individuals of the same species almost always
exceed in height, weight, vigor of growth and frequently also in fertility,
the corresponding individuals produced by self-fertilization." (3b, p. 465.)

"The result," says von Tschermak, "formed the first instigation to my
researches, which, on the one hand, on account of the significance of this
question for the science of plant breeding, on the other hand, on account

PLANT HYBRIDIZATION BEFORE MENDEL 351

of the incompleteness of the observation-material in Darwin's case, cal-
culated upon a larger scale (on the basis of an exact numerical test)
were intended for the investigation of this exceptional case. As I became
acquainted with the further literature in question upon experiments car-
ried out with peas, I introduced in addition a series of other experi-
ments, which deal with the inheritance of the characters of unequal
value, dominant or recessive (Mendel), and which should especially
determine exactly the results of the immediate influence of foreign
pollen upon the structure of the fruit produced thereby, or the simul-
taneous operation of two pollen species in many-seeded fruits. The ex-
periments were begun in the year 1898, in the Botanical Garden in Ghent,
the Director of which. Professor MacLeod, has bound me in gratitude
through the active interest which he manifested toward my researches."

The writer proceeds to comment on the fact that, in recent
times, methods for the artificial crossing of grain varieties had
been published in large measure, but for peas in lesser detail.

"Concerning the process of the artificial crossing of peas there exist
only scanty statements." (3b, p. 468.)

Mendel's work is thus alluded to {ib.^ p. 468) :

"Crossing experiments with peas for purely scientific purposes, have
been carried out by Gartner £'Bastardierung im Pflanzenreiche,' 1849,
pp. 7iff.) ; Darwin ('Variation,' Chaps. 9, 11; 'Cross- and Self-fertiliza-
tion,' p. 151) ; and Gr. Mendel ('Verhandlung der Naturforscher Verein,'
Briinn, 1865, IV Bd., pp. 3 ff.)."

The experiments of von Tschermak in 1898 comprised ten
pots for each variety used, each with 4-5 seeds, the two most vig-
orous being left to grow to maturity. In this experiment, the re-
sults of close and self-fertilization were also considered.

"The experiments pursued primarily the same end, of obtaining ma-,
terials for evidence regarding self-fertilization and crossing, in order to
be able to repeat in the following year, the test experiments of Darwin."
(3b, p. 476.)

"The continuation of the experiment was carried out in the spring of
1899, in a walled garden in Esslingen [Lower Austria]." {ib., p. 477.)

Since this portion of the experiment does not touch the Men-
delian question, it need be no further noticed.

Later in the course of the same experiment, the following state-
ment occurs:

"My experiments showed first, that frequently, and indeed under dif-
ferent conditions, even in the constitution of the seeds the influence of
the pollen originating from the other variety could be recognized." {ib.,
p. 505.)

Commenting further, it is stated :

352 PLANT HYBRIDIZATION BEFORE MENDEL

"The previously listed differences of the same structure, in other words,
the characteristic 'characters of the individual varieties, manifested them-
selves in respect to inheritance, as not being equivalent. Regularly, the
character in question, of the father or mother plant, comes exclusively
into expression (dominating characters according to Mendel), in con-
tradistinction to the recessive character of the other parent plant, which,
however, is accustomed to come again to light in part in the seeds of
the hybrid plant. As dominating, in harmony with the statements of
Mendel, the round, smooth form as opposed to the cubical and deeply
wrinkled one; the yellow color of the storage tissue as opposed to the
green color, and indifferently, whether the seed of the pollen parent
possessed this character (as likewise Mendel)." (ib., pp. 505-6.)

The author notes that :

"In individual cases of artificial crossing of different varieties of peas,
a direct influence of the foreign pollen upon the seeds could be deter-
mined. To these effects quite definite combinations led with regularity.
The characters which were taken into consideration for the recognition
of such an influence concerned the form of the seeds and the color of
the storage tissue. The seeds of the varieties used were either round, and
at the same time smooth, or only gently wrinkled, mostly somewhat
oblong through close packing in the pods, or else they were more or
less cubical (Pisu?n quadratum), and at the same time deeply wrinkled.
The color of the storage tissues is either yellow, or green in various
shades ; the pod is mostly dirty-to-yellowish white, or it shows a more
or less marked yellowish-green to green shimmer, which proceeds from
tannin-like pigments which appear partly in the hard layer, and partly
in the parenchyma layer, or in both together. With the colors mentioned
of the seed-coat white flower-color is always correlated. Gray, gray-
brown, leather-brown, often dotted with violet, as well as green with
violet spots, is combined with flowers which show a violet-colored stand-
ard, and purple wings, with red markings in the leaf axils." (p. 505.)

The first distinct mention in the paper of Mendelian results is
in connection with the height experiment {ib., p. 476) :

"The products of crossing further afford opportunity to study the
direct influence of the pollen upon their color and form. Such an in-
fluence showed itself in crosses between differently colored and differ-
ently formed peas, for definite combinations, with the greatest regu-
larity."

The above experiment, having been planned for the different
purposes hitherto named, was not followed up from the Men-
delian standpoint.

The author finds (ib., p. 5^7) •

"The appearance of the dominating and of the recessive character
is not a purely exclusive one. In individual cases, I could, on the con-
trary, detect with certainty a simultaneous appearance of both inter-
mediates.

PLANT HYBRIDIZATION BEFORE MENDEL 353

"In respect to color, Telephone No, 2, with cotyledons yellowish or
whitish-green, sometimes also completely clear yellow, X Pois d'Auvergne
No. 9, with cotyledons pure yellow ; the F, hybrid seeds were found to
be in general yellow, but with plainly visible green spots, [ib., p. 507.]
In like manner, the crossing of Couturier No. 6, with orange-yellow
cotyledons, with Express No. 14, with light green cotyledons, instead of
giving pure yellow, gave a transition tone between yellow and green.
Pois d'Auvergne, No. 9, cotyledons dodder-yellow-orange, with Telephone
No. 2, yellowish or whitish-green, gave instead of pure yellow, a green
spotting on the otherwise yellow cotyledons." (ib., p. 507.)

"Likewise in respect to form, cases are not lacking in which the ordi-
narily dominating compared with the ordinarily recessive in a certain
relationship." (ib., p. 508.)

The cases, however, do not appear to have been quite so clearly
defined as the preceding.

After an extended further discussion of the relation of the
pollen to the character of the pod in the seed parent, von Tscher-
mak remarks as follows, citing the older literature of Darwin,
Gartner, Knight and Laxton :

"My experiments have most points of resemblance to the observations
of Gregor Mendel, who worked with 34 varieties of peas. Fro7n his is
derived the above adopted and strengthened conception of dominating
and recessive characters. In seeds obtained through artificial pollination,
he observed the former (yellow) coloration, and roundness. His results
with respect to the crossed plants, studied through several generations,
will have to be entered into later.

"It must be cited, as the especial service of this observer, that he recog--
nized the regularly unlike value of the different characters for inheri-
tance, and demonstrated it clearly, for the especially adopted species,
Pisum sativum." (pp. 513-14.)

This is the first extended reference to Mendel in this paper.
One of von Tschermak's observations referred to a phenomenon
under the name used by Gartner, of Pravalenz (prepotency).

Twelve crosses, with reciprocal crosses, constituted the experi-
ment. Quoting:

"In the last four cases, of form, and in part color-difference of the
parent sorts, and of indicated commingling of characters in the product,
each of the parent sorts showed (relatively) more influence upon the
constitution of the crossed product, whe^ it furnished the seed-pod, than
when it furnished the pollen." (ib., p. 514.)

The last thirty-four pages of the memoir, constituting Part IV

of the von Tschermak paper, are devoted to the subject, "Beo-

bachtungen an den durch kiinstliche Kreuzung erzeugten Misch-

Hngen." (Observations on hybrids produced through artificial

crossing.)

354 PLANT HYBRIDIZATION BEFORE MENDEL

In the whole of the paper, the author by preference uses the
word "Mischling" for crosses made between varieties of the same
species.

"since the forms of peas used by me, according to the general view at
present, represent varieties of one and the same species, Pisum sativum
L., I designate the products of their crossing (heteromorphic xenogamy)
as 'Mischlinge,' not as hybrids ['Bastarde']." {ib., p. 521.)

This paragraph clearly shows the transition state of mind be-
tween the earlier point of view regarding "hybrids," in which
the product was regarded as a whole, and from the a priori stand-
point of the degree of closeness of relationship of the two par-
ents, and demonstrates that the idea of the crossing of competi-
tive characters, i.e., of what has been later denominated the con-
tending of two members of an "allelomorphic" pair, as being a
universal phenomenon no matter what the degree of relationship
of the parents, had not yet gained a certain foothold. In von
Tschermak's paper of 1900, we still see that the crossed plant
product was being thought of as a whole, rather than in terms of
its individual character-factors regarded singly.

Considerable experimental work follows in the von Tschermak
paper on the relative height, etc., of self-fertilized individuals,
individuals from crosses upon the same plant, and on different
plants of the same variety, in the case of peas. The following
conclusion was arrived at:

"From the whole of my experiments it results that, in the sorts of
Pisum sativum used, a cross between different flowers of the same indi-
vidual, as between flowers of different individuals of the same variety,
brings no advantage to the descendants, in comparison to the plants pro-
ceeding from self-fertilization." {ib., p. 522.)

In this conclusion the writer confirms wholly Darwin's experi-
ments.

A further conclusion from the series of experiments is arrived
at in general, that :

"Among the twelve hybrid forms [Mischlingsformen] cited, there ac-
cordingly results in probability a simple taking-over of the paternal
height-character, but no proof of a height excess through crossing in
itself, in contrast to self-fertilization. The hybrids in question stand in
height either between the parents, and indeed nearer the higher mem-
ber, or resemble them." {ib., p. 530.)

From further cases of exceptions, he concludes :

PLANT HYBRIDIZATION BEFORE MENDEL 355

"The hybrids accordingly appear, on the crossing of certain varieties
of Pisum sativum, to gain an access of height, in comparison with the
paternal and maternal variety grown from self -fertilized products; with
other combinations, on the other hand, such an advantage of crossing, as
compared with self-fertilization, is lacking, and there is merely to be
found an influence of the paternal variety on the height of the hybrid."
{lb., p. 531.)

Further, it is stated:

"with respect to the relative influence (or the relative weight) of a
difference in the height-character of the paternal and the maternal va-
riety, my conclusions furnish the following :

"The higher type prevails, indifferently as to whether it is due to the
father or the mother. The derivatives of a relatively low variety, after
pollination with the pollen of a relatively high one, appear, as Andrew
Knight already observed, relatively strongly increased in height. In the
reverse case, the hybrids are generally little, if at all, lowered in height."
{ib., p. 532.)

The attitude of mind prevailing at the time of the discovery of
Mendel's paper, is singularly brought out even in the paper of
von Tschermak, in the following form of statement :

"in the seeds of the hybrids [Mischlinge], obtainable in the first gen-
eration from self-fertilization, the characters yellow and smooth, evi-
denced themselves precisely as in the case of the cross-pollinated seeds
of the mother plant, as being of higher value or hereditary potency, than
the characters green and wrinkled, while in the case of the artificial
breeding of products of heteromorphic xenogamy the first-named char-
acters are almost exclusively dominant: the latter, 'recessive' ones, only
come to light pure in individual cases (or as admixture) ; those characters
in the seeds of the first hybrid generation attain, only in the majority of
cases, to development pure ; in the minority of cases, the 'recessive' char-
acters appear.

"In the first case, there exists an almost absolute dominance ; in the
second a mere prevalence (in certain relationships)." {ib., pp. 534-5.)

This statement appears to show that, in the investigator's mind
at that time, the old idea of a sort of "prevalence of potency"
existed, which, in what we now call the F^ generation, gave
almost exclusive dominance ("bei der kiinstlichen Erzeugung von
Produkte hetermorpher Xenogamie, die erstgenannten Merkmale
fast ausnahmlos dominierend sind, die letzteren, 'rezessiven,' nur
in Einzelfallen rein, [oder als Beimischung] zur Tage treten,"
etc.). {ih., p. 535.)

However, in what is now known as the Y^ generation, referred
to by von Tschermak as "an den aus Selbstbefruchtung erhal-
tenen Samen der Mischlinge in erster Generation" (p. 535) » it is

356

PLANT HYBRIDIZATION BEFORE MENDEL

stated, not that an absolute ratio exists, but that "the characters
yellow and smooth," are "of higher value or hereditary potency
than the characters green and wrinkled (die Merkmale gelb und
glatt als von hoheren Werthigkeit oder \'ererbungspotenz wie die
Merkmale griin und runzelig)." {ib., p. 534.)

However, in an immediately following statement of the numeri-
cal results with these characters, the writer reports as follows :

(1) Pot-grown hybrid plants

Yellow
61
Green smooth
15

(2) Field-grown hybrid plants

No. of plants Yellow

1 79

1 52

203

Green

Ratio

2.06 : 1

Green wrin

kled

Ratio

3.00 : 1

Green

Ratio

2.70

: 1

2.70

: 1

3.00

: 1

In another case reported from six plants, the ratio of two char-
acters was found as follows:

Yellow smooth

435

Green smooth

148

Yellow wrinkled

116

Green wrinkled

or a ratio of 9:3:3:1. (ib., pp. 526-8.)

The conclusion is then stated (3b, p. 535) as follows:

"The number of the bearers of the dominating or as the case may he
prevailing characters is thus related to the bearers of the recessive about
aszw"

We thus find, at the beginning of the period of Mendelian in-
vestigation, the use of the concept "dominating" or "prevailing"
instead of "dominant," reflecting in this respect the influence of
the preceding generations of the older hybridizers rather than
the direct influence of Mendel himself.

For "the products of those hybrids, whose parents were differ-
ent in two seed-characters" (3b, p. 535), the following experi-
mental results are further given :

PLANT HYBRIDIZATION BEFORE MENDEL 357

Pot-grown plants

(2)

Field-grown

plants

characters Numbers

Ratios

Numbers

Ratios

Yellow smooth 28

9-3

504

8.3

Green smooth 12

4.0

180

3.0

Yellow wrinkled 20

6.6

145

2.4

Green wrinkled 3

1.0

Von Tschermak's final conclusion agrees with Mendel's re-
sults, and is stated as follows:

"From this essential approach to the average value, there results, in my
judgment, the conclusion, that the combination of two dominating (or
recessive) characters in the one parent form results in the same rela-
tionship in the seed product of the hybrids, as the characters in question
do when isolated. An alteration of the value, or an increase of the pre-
valence, does not thereby enter in." (3b, p. 536.)

This concludes the account, rather extended in detail, of the
three remarkable, practically simultaneous, discoveries of Men-
del's celebrated papers published in the year 1900. Without regard
to the actual precedence in respect to dates of publication, the en-
tirely independent and practically equal merit of the contributions
of the three separate investigators leaves little room for conten-
tion from the standpoint of the contributions themselves. The re-
markable fact for science of the nearly simultaneous triple re-
discovery of Mendel's Law dwarfs into insignificance the matter
of precedence therein.

BIBLIOGRAPHY

De Vries^ Hugo.

(a) Das Spaltungsgesetz der Bastarde. Ber. d. d. bot. Ges.
18:83-90. 1900.

(b) Sur la loi de disjonction des hybrides. Comptes Rendus
de I'Acad. des Sciences. Paris, 130:845-7. 1900.

18:435-43- 1900.

(d) Intracellular Pangenesis. 270 pp. 8vo. Chicago, 1910.

(e) Intracellulare Pangenesis. 212 pp. Jena, 1889.

358 PLANT HYBRIDIZATION BEFORE MENDEL

2. Correns, C.

(a) G. Mendels Regel iiber das Verhalten der Nachkommen-
schaft der Rassenbastarde. Ber. d. d. hot. Ges. 18:158-
68. 1900.

3. Tschermak^ E. von.

(a) tJber kiinstliche Kreuzung bei Pisum sativum. Ber. d.d.
bot. Ges. 18:232-9, Article 26. 1900.

Also in :

(b) Zeitschr. fiir das landwirtsch. Versuchswesen in Oester-
reich, 3 Jahrg. pp. 465-555, 1900.

CHAPTER XII

35*. The Contribution of William Bateson.

A HISTORICAL survey of the circumstances surrounding
the discovery of Mendel's paper in 1900 would be incoin-
.plete without including the contribution of Professor Wil-
liam Bateson (now deceased), formerly of Cambridge University,
then director of the John Innes Horticultural Institution of Mer-
ton — the first translator and editor of Mendel's papers into
English.

For a considerable time Bateson had worked upon the phe-
nomena of variation, and particularly upon what was designated
"discontinuous variation," as a means of evolution. In this par-
ticular field Professor Bateson was the most conspicuous investi-
gator in the English-speaking world, in a somewhat similar man-
ner as, under the thesis of the Mutation Theory, De Vries re-
mained upon the Continent. In this connection, Bateson had pub-
lished a considerable volume of material in his "Materials for
the Study of Variation, treated with Especial Regard to Discon-
tinuity in the Origin of Species." (593 pp., London, 1894.)

At the sessions of the International Conference on Hybridiza-
tion (the Cross-breeding of Species), and on the Cross-breeding
of Varieties, called at the invitation of the Council of the Royal
Horticultural Society, and held at Chiswick and London (July 11
and 12, 1899), Bateson presented a paper entitled "Hybridiza-
tion and cross-breeding as a method of scientific investigation,"
read July 11, 1899, and published in the Hybrid Conference Re-
port (Jour. Roy. Hort. Soc, Vol. 24, pp. 59-66).

In this paper it is interesting to note Bateson's attitude of mind
during this transition period. Bateson says :

"The first question was : How large are the integral steps by which
varieties arise *? The second question is : How, when they have arisen, are

Plate XLVII. Professor William Bateson, Director of John Innes Horticultural Institutioa,
(deceased).

PLANT HYBRIDIZATION BEFORE MENDEL 361

such variations perpetuated ? It is here especially that we appeal to the
work of the cross-breeder. He, and he only, can answer this question :
Why do not nascent varieties become obliterated by crossing with the
type form ?" (p. 62.)

It is interesting to note how^ completely Bateson's attitude to-
ward the phenomenon then known as "discontinuous variation"
had prepared him, as in like manner also De Vries was prepared,
to take the analytical point of view toward the hybridization
process, even before the publication of Mendel's results, as the
following quite remarkable passage clearly indicates:

"The recognition of the existence of discontinuity in variation, and of
the possibility of complete or integral inheritance when the variety is
crossed with the type, is, I believe, destined to simplify to us the phe-
nomenon of evolution perhaps beyond anything that we can foresee. At
this time we need no more general ideas about evolution. We need par-
ticular knowledge of the evolution of particular forms. What we first
require is to know what happens when a variety is crossed with its
nearest allies. If the result is to have a scientific value, it is almost abso-
lutely necessary that the offspring of such crossing should then be ex-
amined statistically. It must be recorded how many of the offspring re-
sembled each parent, and how many showed characters intermediate
between those of the parents. // the parents differ in several characters,
the offspring must he examined statistically, and marshalled, as it is
called, in respect to each of those characters separately. . . . All that is
really necessary is that some approximate numerical statement of the
result should be kept." (Italics inserted.) (p. 63.)

If Mendel's paper had never come to light, it is more than
probable that investigation would have ultimately been directed
to the crux of the method of inquiry, by this utterance of Bate-
son's, remarkable for the time, and noteworthy as being the first,
and indeed the only clear postulation of the terms of a scientific
basis for an investigation of the descent of characters, in all the
literature antecedent to the re-discovery of Mendel, viz :

"That if the parents differ in several characters, the offspring must he
examined statistically, and marshalled, as it is called, in respect of each
of those characters separately!' (Italics inserted.) (p. 63.)

This remarkable statement progressed beyond any point of
view theretofore expressed, and should be preserved as a memo-
rial to the prescience of Professor Bateson, the first champion of
Mendelism in the English-speaking scientific world.

Bateson's standpoint is further illustrated by the following
statement :

/-.f-.-A

Pr.ATF XLVIII. Facsimile of letter of Mendel to Nageli, with signature. Furnished by Professor
Correns.

PLANT HYBRIDIZATION BEFORE MENDEL 363

"Cross-breeding, then, is a method of investigating particular cases of
evolution one by one, and determining which variations are discontinuous
and which are not, which characters are capable of blending to produce
a mean form and which are not. It has sometimes been urged against
this method of investigation that the results are often conflicting. It has
been said that such work will only lead to accumulations of contradictory
evidence. It is, however, in this very fact of the variety of results that
the great promise of the method lies." (p. 64.)

From the whole of the above, it appears that to Bateson's mind,
at that time, one of the principal purposes of hybridization was
to determine in what cases blending occurred, and in v/hat cases
characters were discontinuous in their descent, which was the
first prerequisite to an actual experiment to determine the facts,
and the credit for which, as a prolegomenon, unquestionably be-
longs to Bateson alone.

As illustrations of "discontinuous" inheritance after crossing,
Bateson cites the case of the crossing of Matthiola incana^ a hairy
species, and its smooth variety, crossed by Trevor Clarke, re-
porting the fact observed that :

"On crossing these two varieties the offspring consisted entirely of com-
pletely hoary and completely glabrous individuals, no intermediate being
present." (p. 64.)

The case of Lychnis diurna (hairy), crossed with its glabrous
variety by De Vries, is also cited.

"All of the first generation of cross-breds inherited the hairiness in
its complete form : when, however, these plants were crossed again with
the smooth form, the result was a mixed progeny, of which some were
hairy, and others smooth." (p. 64.)

A third case was given as that of Biscutella laevigata^ reported
from the investigations of Miss E. R. Saunders, one of Bateson's
pupils. The species type is a hairy plant of the Alps, with a local
variety having the leaf surfaces smooth ; the smooth form is
found to occur abundantly with the hairy types, intermediates
seldom occurring.

"The result of artificial cross-breeding went to show that of the young
seedlings of mixed parentage some were hairy, some smooth, and a good
many intermediate. But as these seedlings grew, the hairy and the smooth
retained their original characters, while the intermediate ones gradually
became smooth. The transition was not effected by actual loss of hairs,
but, after the first few leaves of intermediate character, the leaves subse-
quently produced were smooth." (p. 65.)

Bateson goes on to say :

364 PLANT HYBRIDIZATION BEFORE MENDEL

"In all these three cases there is discontinuity, the intermediates be-
tween the varieties being absent or relatively scarce. Nevertheless, on
examination, it is found that the discontinuity is not maintained in the
same way in the different cases. The transmitting powers of the one va-
riety in respect of the other are quite different in each case, and it must,
I think, be admitted that we have here a fact of great physiological
significance. In each of the three cases enumerated, the two varieties are
seen to stand towards each other in a different relation, and in each the
mechanism of inheritance works differently." (p. 65.)

Bateson finally closes with the following significant comment
upon the contention that the results of crossing are uncertain,
sometimes one result occurring, and sometimes another :

"This, of course, merely means that the problem must he studied on
a scale sufficiently large to give a statistical result. There is here an al-
most untouched ground on which the properties of specific characters
can be investigated." (Italics inserted.) (p. 66.)

On May 8, 1900, not quite a year after the address referred to
above, and almost immediately after the appearance of the papers
from Holland, Germany, and Austria on the subject of the Men-
delian investigations. Professor Bateson presented to the Royal
Horticultural Society, the results of the then recently published
reports of De Vries, Correns, and von Tschermak, together with
an outline of Mendel's results, in a lecture entitled "Problems of
heredity as a subject for horticultural investigation," published
in the Journal of the Society, Vol. 25, pp. 54-61, in which he con-
cludes as follows regarding the Mendelian results :

"The numbers with which Mendel worked, though large, were not
large enough to give really smooth results ; but, with a few rather
marked exceptions, the observations are remarkably consistent, and the
approximation to the numbers demanded by the law is greatest in those
cases where the largest numbers were used. When we consider, besides,
that Tschermak and Correns announce confirmation in the case of Pisum,
and De Vries adds the evidence of his long series of observations on other
species and orders, there can be no doubt that Mendel's law is a substan-
tial reality; though whether some of the cases that depart most widely
from it can be brought within the terms of the same principle or not
can only be decided by further experiments." (p. 59.)

This address may be said to constitute the first public intro-
duction of Mendel's results to English-speaking workers by an
investigator of standing. Bateson followed soon after with a com-
plete translation of Mendel's paper (Jour. Roy. Hort. Soc, 1901,
Vol. 26, pp. 1-32^), and later (1902) by its publication in the

1 Mendel's paper, "Experiments in Plant Hybridization," appears on

PLANT HYBRIDIZATION BEFORE MENDEL 365

form of a small octavo volume entitled "Mendel's Principles of
Heredity; A Defence," now out of print. Concerning these publi-
cations he says later, in the preface to his "Mendel's Principles of
Heredity" :

"The translation of the first of Mendel's two papers, based on a draft
prepared for the society by Mr. C. T. Druery, was printed in the Royal
Horticultural Society's Journal, 1901. With modifications I published it
separately in 1902, giving a brief summary of Mendelism as then de-
veloped, under the title 'Mendel's Principles of Heredity; a Defence.'
The object of that publication was to put Mendel's work before the Eng-
lish-speaking peoples, and to repel the attack which the late Professor
Weldon had recently made on Mendelian methods and the conclusions
drawn from them. The edition was at once sold out, but I did not reprint
the book. As a defence it had served its purpose."

In 1909, under the title "Mendel's Principles of Heredity,"
Bateson published, in a volume of about four hundred pages, the
results of the Mendelian investigations made by himself and his
fellow-workers, together with results from the general field, al-
ready very considerable. In the second part of this volume there
appeared a biographical notice of Mendel, and translations of
Mendel's papers "Experiments in Plant-Hybridization" and "On
Hieracium-Hybrids obtained by xA^rtificIal Fertilization." This
work was reprinted with appendixes in 1913. It is only justice to
Professor Bateson to say that the general recognition of Mendel's
work and Its fundamental significance In England and this coun-
try Is largely due. In Its Inception, to his clear-sighted compre-
hension of the requirements for an Investigation of the problem
of heredity, and his Immediate and ready appreciation of the Im-
portance of Mendel's results, based upon his own prolegomenon
of opinion, and as confirmed by the work of Mendel's three dis-
coverers. To Bateson's prompt and courageous championship of
the then comparatively obscure matter of the Mendelian Law, the
first progress In English-speaking quarters of the principles in-
volved Is therefore chleflv to be accredited.

pp. 1-32 of Vol. 26 for 1901-02. The paper is prefaced by a two-page
Introductory note by W. Bateson. The name of the translator does not
itself appear. In the first paragraph of his note Bateson writes :

"It will consequently be a matter for satisfaction that the Royal Horti-
cultural Society has undertaken to publish a translation of this extraor-
dinarily valuable contribution to biological science."

366 PLANT HYBRIDIZATION BEFORE MENDEL

Finally, it is to Professor Bateson, that the initiation of the
first definite Mendelian terminology after 1900 is due, the words
"allelomorph," "homozygote" and "heterozygote" having been
proposed by him as early as 1901, in the First Report to the
Evolution Committee of the Royal Society, presented for publica-
tion December 17 of that year. In this report, appearing less than
two years after the rediscovery of the Mendel papers, Bateson
made the following statement (p. 126) :

"We thus reach the conception of unit-characters existing in antagon-
istic pairs. Such characters we propose to call allelomorphs, and the
zygote formed by the union of a pair of opposite allelomorphic gametes,
we call a heterozygote. Similarly the zygote formed by the union of
gametes having similar allelomorphs, may be spoken of as a homozygote.
Upon a wide survey, we now recognize that this first principle has an
extensive application in nature. We cannot as yet determine the limits of
its applicability, and it is possible that many characters may really be
allelomorphic, which we now suppose to be 'transmissible' in any degree
of intensity."

This concludes the discussion, made purposely as complete as
possible, of the facts and documents surrounding the discovery
and bringing to light of Mendel's celebrated paper in 1900. It is
believed that this should form a fitting conclusion to the attempt
to give as complete an historical account as possible of the data
upon hybridization in plants during what may be called the pre-
Mendelian period — the period from Kolreuter's first publication
in 1763 to 1900.

INDEX

ACCLIMATIZATION, vicws of William

Herbert on, 97
affinity, sexual, 170, 178, 187-8, 193-4
Aegilops, 128, 129
alsike clover, hybrid origin of, 28
Amaryllis, hybrid, 142
Amaryllidaceae, 100
Antholyza, Linnaeus' experiments,

20
Antirrhinum, Darwin's ratio in

crosses of, 235
apple, hybrid, 92
Aristotle, 12

BANANA, Linnaeus' experiment with,

Bassett hounds, inheritance in, 251-8

Bateson, William, 359-66 ; Mende-
lian anticipation by, 362

Biscutella, hybrids of, 363

Bryanthus, color-inheritance in, 266 ;
hybrid, 264; intermediacy in, 264,
266

Bradley, Richard, 62; experiment
with tulips, 65; on Fairchild's hy-
bridization experiment, 65

Calceolaria, hybrids of, 183
Camellia, inheritance in, 143; varie-
gation in, 138
Camerarius, R. J., 12; and hybridi-
zation, 15
Cannabis, 12, 20; see also hemp
characters, contrasting, in crossing.
121, 279, 292, 317-18; latent, 203.
235-6, 243; linked, 105, 143. 341 ;
multiple, 303 ; see also unit-char-
acters ; segregation of, see segre-
gation and hybrids
Chamaerops, pollination experiment
with, 70-5

coat-color, inheritance of, in
hounds, 251-8

color, dominance, 87, 89, 90-1, 98,
142, 163, 210, 330; inheritance,
53, 57, 90-1, 97-8. 108, 141, 142,
145-6, 155, 156, 163, 164, 174.
175-7, 210, 212, 254-8, 264, 265.
266, 303, 350, 352, in Bryanthus,
266, in Gloxinia, 142, in Hedy-
chium, 266, in Lupinus, 144-7, in
Menziesia, 266, in Pisum, 87-91,
104-10, 151, 171-4, 340-1, 355-7,
in Rhododendron, 265-6; varie-
ties, crosses of, 210

Correns, 335-43

cross and self-fertilization, see ferti-
lization ; effect of , .89, 90, 91, 116,
162, 163

crossing, effect of in leguminous
plants, 108, 162, 163-4, 171-4, 175'
352 ; effect of on first-generation
seeds, 162, 174, 175; methods in,
97, 1 13-14, 1 15, 155 ; of species and
varieties, 127, 151, 208, 210

Cruciferae, crosses of, 122

Cucurbitaceae, crosses of, 121-3

Cypripedium, 265

Cytisus, adami, 138, 267, 269

Darbishire, 276

Darwin, Charles, 221-40

date culture, ancient, 2-3

date palm, pollination of, l, 5-6,

10-11, 22; date, relation of to

plant breeding, 4-12
Datisca, experiments with, 21.
Datura, crosses of, 53, 58, 130, 134-5,

168, 194-5, 330; disjunction in,

130
De Vries, 321-35.
Dianthus, chimaera, 156; crosses of,

51, 52, ss,_ 56, 57,. 62, 65, 163, 195,

264; dominance in, 163; intcrme-

368

INDEX

diacy in, 56, 264; reciprocals of,
52, 55-6 ; species-hybrids, domi-
nance in, 56, 163

Digitalis, crosses of, 195, 206, 260-2

disjunction, 131-3, 324-6

dissociation of characters, see dis-
junction, segregation, and hy-
brids, segregation of

dominance, 52, 56, 87, 108, 116, 121,
142, 163, 210, 215, 234-5, 236, 238,
259, 279, 292-4, 324-5, 329, 330,
349-50, 351-3, 355-7; color, 87, 89,
103, 142, 163, 210; "dominste," use
of word, 121, 163, 356; in species-
crosses, 52, 56, 163, 170; see also
hybrids, dominance in

doubleness, dominance of, 52, 56 ;
in flowers, 97, 98, 143, 155

double-pollination, 100. 209

Drosera, crosses of, 272-4

E
"Epistola De Sexu Plantarum" of

Camerarius, 12
Erica, hybrid, 265
evolution, method in, 203, 241-5
eye-color, inheritance of, 243, 248-50

FACTORS, in inheritance, 181, 271-2,

303,.33i, 332, 334-5
Fairchild, Thomas, experiment in

hybridization, 62, 65
fertility, in cross and self-fertilized
plants, 224-6, 227-32, 236-7 ; of hy-
brids, see hybrids ; ratio of, in
cross and self-fertilized plants,

237
fertilization, see also crossing;
cross and self, 87. 100, 188, 224-6,
226-32, 348-9; difficulties in, 162;
effect of, 20, 21, 60-1, 72-5, 162,
188; effect of cross, 173, 174, 176;
experiments in, 20-2, 42-3, 49,
71-5; male and female elements
in, 44, 46, 56, 70, 75, 77, 89. 91-3,
181-2, 193, 198, 209, 270, 318, 353;
nature of, 38-9, 44, 46, 47-8, 75;6,
232; of maize, 12-13, 68-9; role
of insects in, see insect-pollina-
tion ; theories regarding. 38-9. 40,
42-4, 46, 47-8, 57, 75-6, 98-9, 100-1,

193, 334

fig, fertilization of, 39

Focke, W. O., 204-16; details of
work, 211 ; estimate of Knight,
93; opinion of Gartner, 177

Galton, sir Francis, 241-59; estimate
of work, 258-9

Gartner, C. F. von, 164-78; list of
crosses, etc., 168; opinion of Kol-
reuter, 78; reference to Knight,

Gleditsch, J. G., 70-7 ; experiments
in pollination, "joff.; theory of
fertilization, 75-6

Gloxinia, color-dominance in, 142;
hybrid, 142

Godron, D. A., experiments in hy-
bridization, 124-9

Goss, John, crossing of peas, 102-3;
reference of Focke, 214-15; refer-
ence of Knight, 91

Grew, Nehemiah, 62-4

Haartmann, Johannes, hybrids, dis-
cussion of, 24, 28, 29

Hedychium, 264, 266 ; color-inheri-
tance in, 266; intermediacy in,
264, 266

hemp, Camerarius' experiments, 12

Henslow, J. S., 260-3

Herbert, William, 94-102; acclimati-
zation, views on, 97 ; cross of
Crinum, 97 ; cross of Hippeas-
trum, 97; cross of Rutabaga, 98;
double flowers, experiments with,
97-8 ; estimate of Kolreuter, 94 ;
fertilization, views on, 98-9, lOO-l ;
hybrids, views on, 95-6; species-
crosses, 99 ; summary of work of,
101

heredity, bisexual, 271-2; Galton's
law of, 251-2, 258-9; method in,
Galton, 244-6; nature of, 147-8-9,
203-4; unisexual, 271

heterosis, 89, 90, 192. 226^.

Hibiscus, hybrid, 99 ; intermediacy
in, s'3 ; pollination of, 60-1

Hoffman, H., Mendel-citations, 216-
18

llinnulus, 19

hybridization, see also hybrids;

INDEX

369

plant-improvement by, 22-3, 96-7,
113, 154, 155
hybrids, abnormalities in, 210; be-
havior of, 191, 207, 209-10; char-
acteristics of, 54-5, 149, 194> 196;
classification of, 168, 179; color-
varieties, hybrids of, 210; discus-
sion of (Linnaeus), 23, 24; dis-
junction in, 131-2; disordered
variation in, 133-4, 135? domi-
nance in (see also dominance),
89, 103, 116, 121, 142, 163, 279,
292-4, 325, 329, 330, 340-1, 349-50,
351-3; factorial components of,
271, 293-4, 312, 318; fertility of,
24, 45, 46-7, 95-6, 101, 123-4, 127,
128, 129, 130, 162-3, 180-1, 187-8,
191, 192, 207, 208, 223, 228-9, 237-8,
272 ; first generation, uniformity
of, 58, 130, 134, 136, 209, 282, vari-
ability in, 189, 190, 194, 195, 277,
vigor of, 44-5, 47, 196, 228-30; in-
termediacy in (see also heredity
unisexual afid bisexual) , 28, 44, 53?

56, 57, 58, 65, 103, 130-1, 135, 141,
142, 151-3, 155, 163, 181, 183, 188
189, 191, 192-3, 195-6, 207, 234,
236, 237-8, 262, 264-6, 268-70, 274,
282; list of Gartner, 168. Haart-
mann, 29, Kolreuter, 36, 46, 48, ^o,
54, SS> 58, 61 note, Wichura, 180
Wiegmann, 162 ; mating of, 238-9 ;
microscopic structure of, 267-70,
272-4; nature of 23. 24, 45, 54-5,
100, 130, 131, 133, 135, 141, 154.
171, 180-1, 183, 188, 190, 191, 193-
4, 196, 210, 334; non-fusion of
characters in, 121, 180, 234-5; nu-
merical relations in, 107-8, 136,
144, 145-6, 172-3, 175-6, 235, 27 >
81, 294-5, 296, 315-17, 325, 327-31-
340-1, 356-7; race and variety,
210; reciprocal, 47, 48, 52, 53, 56,

57, 58, 134, 151-3, 181, 187, 189,-
191, 19?, 208, 223-4, 237, 2Q3, 350,
3J3; reversion in, 110, 126, 12S-Q,
132, 169, 189, 192, 206, 236, 237-8
238-9 ; rules or laws regarding, 23,
24, 87, 126, 149, 168-9, 171, 187-9,
190-2, 209-10. 282, 290, 291, 30^,

31 1, 312, 318, 324-?, 328-0, 332, 311,
342; second-generation, 125, 128-9,
131> 133, 136, 164, 169, 176, 189,

190, 194, 210, 238, 282, 293-4; seg-
regation in, 108, 121-2, 122, 125,
128, 131, 132, 135, 140, 145-6, 151,
156, 162-3, 169, 174, 176, 293.5,
298-9, 303, 305-6, 307-8, 325, 328-9,
332, 333-4' 340-1 ; species-hybrids,
42,62,99, 151-4, 180, 183, 189, 190,

191, 192, 194, 195, 196, 207-8, 210,
223 ; species-hybrids, sterility of,
127, 153, 154, 180, 191, 194-5, 262,
272; sterility of, 24, 43, 45, 9',
126, 127-8, 12Q, 141, 183-1, 187-*^,
191, 194-5, 207, 210. 224-6, 236-',
272; systematic relationship in,
95-6, 161, 162, 183, 187, 188, 190,
191, 193, 206, 207-8. 210, 223, 2"'7,

272 ; "true" and "false," 183 ; uni -
characters in (see also unit-char-
acters), 121, 133, 271-2, 334-5 ; var-
iability, 189, 190, I9<r, 210; var-
iability of first generation, 190, 194,
195; variability of second gener-
ation, 51-2, 134-5, 169, 194; vege-
tative development of, ^^, 90, 127,
141, 169, 170, 180, 189, 192, 196,
206, 210, 228-9; vigor of (see also
fertility and fertilization), 44-5,
SS, 89-90, 99-100, 127, 141, 169,
180, 192, 194-5, 196, 205-6, 210,
226-7, 228-9, 231, 232, 265, 267;
zygomqrphic forms, hybrids of,
208, 235.

IDIOPLASM, evolution and, 203 ; Na-
geli on the, 197-204; phylogenetic
development of, 201 ; sense-con-
duction through, 202

improvement of plants, 23, 52, ^^,
90, 93, 96-7, 98, 104, 113, 117, 153,
169-70

inheritance, blending, 155, 156, 234,
243, 263-4, 266 ; color, see Color ;
non-blending, 155, 243, 270, 271 ;
of eye-color, 248-50 ; of human
stature, 246-8; of time of flower-
ing, 266; particulate, 241-4; pre-
ponderance in, 198

insect-pollination, 39-40, 81

intermediacy, see hybrids

Iris, pollination in, 39-40.

370

JATROPHA, Linnaeus'
with, 21

INDEX

experiment

Kazwini, 11 . .

Ketmia, number of pollen grains in,

38
Knight, Thomas Andrew, 85-93;
— Darwin Law, 87 ; experiments
with peas, 87-91, hybrid apple, 92 ;
hybrid cabbage. lOO; hybrid cur-
rant, 91 ; hybrids of peach, 91 ;
reference by Gartner, 171; refer-
ence by Focke, 214-15; sex-inheri-
tance in animals, report upon,
92-3
Kolreuter, J. G., 34-6i ; birth and
history, 34; fertilization, views
on, 38, 47-50; first hybridization
experiment, 36, 42-3 ; grasses,
self-pollination in, 39; hybrids,
color-inheritance, 56, 57-8, half-
hybrids, production of, 43-45 in-
creased growth in, 45, SS^ inter-
mediacy in Cucurbita, 58, inter-
mediacy in Dianthus, 56, interme-
diacy in Matthiola, 58, interme-
diacy in Nicotiana, 42, interme-
diacy in Sida, 58, interpretation
of, 45, number of, in Vorlaufige
Nachricht, 36, number of, in 1^^
Vorsetzung, 46, number of, in 2*^^
Vorsetzung. 48-9, number of, in
3te Vorsetzung, 54, number of, in
St. Petersburg experiments, 61, of
Aquilegia, 58, of Ckeirantkus, 58,
of Cucurbita, sS,oi Dianthus, S}-^,
55-7, of Hibiscus, 53, of Leucojum,
53, of Matthiola, 58, of Mirabilis,
53, of Nicotiana, 36. 46-7, 50, SS^
of Sida, 58, of Verbascum, 54. pol-
len, description of, 36-7, 59-60,
self-pollination of, results, 47,
reciprocal, in Dianthus, etc., 57,
sterility in Dianthus hybrid, 56,
sterility in Nicotiana hybrid, 43,
theory regarding, 45-46; pollen,
discussion of, 36-7^ description of,
in Lilium, 59, germination of,
36-8, 59-60, number of grains re-
quired for fertilization, 38; pol-

lination, activity of insects in, 39-
40, experiments in, 49-5 1> i" Hi-
biscus, 60, in Ins, 39, 40, 41 ; sta-
mens, sensitivity of, 58; stigmatic
secretion, nature of, 50-1

Laxton, Thomas, dominance in peas,
108; experiments with peas, 104-
10; Mendelian observation, 109

Lathyrus, Gallon's investigations
with, 245-6

Lecoq, 154-7

Leguminosae, effect of crossr g in,

163, 174
Linaria, Godron's hybrids of, 128-9;

reversion of hybrids of, 125
Linnaeus, 15-29; discussion of hy-
bridization, 23; discussion on dis-
covery of sex in plants, 16-17;
Disquisitio De Sexu Plantarum,
16, 18; experiments with Antho-
lyza, 20 ; experiments with Can-
nabis, 20; experiments with Da-
tisca, 21 ; experiments with Jatro-
pha, 21 ; experiments with Mira-
bilis, 20 ; experiments with Musa,
24; hybrid, of Tragopogon, 22,
of Verbascum, 23, of Veronica X
Verbena, 22 ; opinion of Camera-
rius' work, 19; pollination of date
palm, reference to, 22 ; prize
award, 16

Lobelia, hybrids of, 194

Logan, James, 68-70

Lupinus, crosses of, 144

Lychnis, crosses of, 194, 363

M
Macfarlane, J. M., 262, 274
maize, experiments of Camerarius,
12-13; experiments of James Lo-
gan, 68-70; hybridization of, i57»
174-7 ; see Zea
Masdevallia, hybrid, 264; interm;-

diacy in, 264
Matthiola, crosses of, 58, 363
Mendel, Gregor, 286-318; discovery
of papers, 323, 335*9. 343-7 ; Focke's
references to, 211-14; Hoffman's
references to, 216-18
Mendelian expression by, Bateson,

INDEX

371

362; Darwin, 238; Gartner, 171;
Knight, 87; Laxton, 104, 109;
Nageli, 190; Sageret, 122; Spill-
man, 278, 282-3; Wichura, 181-2

"Mendelian Law," use of term, 342

Menziesia, color-inheritance in, 266 ;
hybrid, 264

Mercurialis, 12-19

Miller, Philip, 66-8

Millington, Sir Thomas, 19, 62

Mimulus, 227

Mirabilis, crosses of, 20, 53, 126,
129, 208; number of pollen grains
in, 38

Montbretia, hybrid, 267

Morland, Samuel, 64-5

Nageli, Carl von, 183-204

Naudin, Charles, 129-136; and Men-
del compared, 132

Nicotiana, crosses of, 36, 42-3, 45,
46-50, SS^ 126, 127, 129, 168

PANGENESIS, Darwin's theory of, 238-
40 ; De Vries' theory of, 332-5

Passiflora, crosses of, 99, 275

peas, hybridization of, Correns, 337-
8, 339-42, Darbishire, 276, Focke
(discussion), 214-15, Gartner,
171-4, Goss, 102-3, Knight, 87-91,
Laxton, 104-10, Mendel, 291-318,
Seton, 103, Vilmorin, 151, von
Tschermak, 345-50, 351-7; linkage
in, 105

Petunia, crosses of, 126, 129, 136

Phaseolus, crosses of, 163-4, 318;
inheritance in, 216-17

Philageria, hybrid, 264, 267, 268-9

Philesia, cross, 268-9

Pistacia, pollination of, 71, 73-4

Pisum, see peas

plant-improvement, see improve-
• ment of plants

Pliny, 12

pollen, description of (Kolreuter),
36-8, 59-60, 77 ; germination of
(Kolreuter), 38-9, 40, 60-1 ; ger-
mination of (Gleditsch), 76;
quantitative effect of, 49 ; refer-
ences to, 20-1, 22, 23, 24, 36-8, 39,
40, 43, 49-50, 51, 52, 56, 58-60, 65,

68, 70, 72-6, 77, 89, 90, 97, 98,
99, 100, 101, 115, 128, 131, 132,
136, 142, 161, 162, 171, 175,
176, 181, 182, 188, 191, 208, 209,
238, 290, 325, 328-9, 338, 349, 351,

352

pollination, self, in grasses, 39

pollination experiments, of Brad-
ley, 64-5; of Camerarius, 12-13;
of Gleditsch, 72-3, 74-5; of Kol-
reuter, 38, 39-40, 43-4, 46, 49, 50-1,
52-3, 59-61 ; of Linnaeus, 20-1, 22,
24; of Logan, 68-70

potency, 170, 198, 233

preponderance in crossing, 170, 181,

195
prepotency, 170, 235, 251, 253-4, 355
Primula, crosses of, 126
pure-line breeding, 150-I

RAPHANUS-BRASSiCA hybrid, 122

ratios in hybrid segregation, 175-6
280-1, 295, 304-5, 325, 329-31, 34c-
1, 350, 356

Ray, 19

Raynbird, hybrid wheat of, 114

reciprocal crosses, differences in, 5~,
170, 187, 195, 223-4, 350, 353 ; diffi-
culty of making, 52, 187, 208, 223,
237 ; identity of, 48, 54, SS, 56, SI-
58, 132, 134, 181, 293; progeny of
91, 195; see also hybrids, recipro-
cal

Regel, 183

reversion, no, 124-6, 192, 236-40;
see also hybrids, reversion of

Rhododendron, crosses of, iCO, 141.
142, 264, 266

rutabaga, hybrid, 98

Sachs, opinion of Sprengel, 81
Sageret, Augustin, 120-3; opinion of

Kolreuter, 77
Sarracenia, crosses of, 263-4
Saxifraga, hybrid of, 264
Scabiosa, germination of pollen

grains, 59-60
seed-characters, in first-generation

crosses, 162
segregation, 120-1, 121-2, 130-3, 140,

145-6, 151, 169, 234-5, 293-5, 304-6,

372

INDEX

340-1 ; somatic, 238; see also hy-
brids, segregation in

self-fertilization and fertility, 188,
224, 229-31, 232, 237; see also fer-
tilization, fertility, and hybrids,
vigor of

Seton, Alexander, experiments with
peas, 102-3; reference of Fccke
to, 214-15

sexual affinity, 178, 187-8, 193-4

sex cells in amphimixis, 181-2, 198,
209

sex-determination, theory of Nageli,
202

sex-inheritance, in animals, report
of Knight upon, 92

sex in plants, 9-14, 16-19, 23, 29,
64-5, 66, 70, 71,. 77-8, 93, 160, 202

sex-limited inheritance, 251

sex-linked characters, 235-6, 253

Shirreff, Patrick, 110-17; wheat-
crossing, 115-16; wheat-crossing,
technique of, 113-15; wheat-
crossing, reference to Knight, 174

species-crosses, 99, 100, 187, 187,
208; see also Kolreuter, Gartner,
Wichura, and hybrids, etc.

species-question, 95-6, 102, 128, 161,
178, 183. 185, 207, 226

Spillman, W. J., 276-83

spinach, experiments with, 12, 66

Sprengel, C. K., 78-83 ; life, 78

stature, inheritance of human, 246-8

sterility, see fertility and hybrids,
sterility of

stocks, see Matthiola

Strabo, 3

sweet peas, Galton's investigations
with, 245-6

Sweet William, Fairchild's, 62, 65

systematic affinity, see hybrids, sys-
tematic relationship in

Thalictrum, hybrid, intermediacy

in, 28
Theophrastus, 12
Tragopogon, hybrid, 22, 43
Trifolium, crosses of, 28, 331
Triticum, crosses of, 113-16, 151-4,

276-82; dominance in, 116, 279-81
Tschermak, E. von, 343-57

UNIT-CHARACTERS, 121, 324, 327, 332,

333, 334-5
unit-theory of heredity, 197, 271

Vaillant, Linnaeus' opinion of, 19

variability, 139, 233-4

variation, bud, 138; "disordered,"
133-55 153; in Camellia, 138, in
Rosa, 138; nature of. 109-10, 1 5'4,
194, 233-4, 271 ; of cultivated
plants, 137, 194; of first-genera-
tion hybrids (see hybrids), 1^9,
190. 194. 195: ^77

variations, origin of, 137, 139-40;
selection of, 139, 140, 153-4

variegations, inheritance of, 142-3

Verbascum, crosses of, 23, 54, 127-S

Verbena, cross of, 28

Verlot, 136-43

Veronica-Verbena hybrid, 22, 26

vigor, of hybrids, see hybrids, vigor
of, fertility, and fertilization

Vilmorin, Henry de, 144, 147-9,

151-4
vilmorin, Louis de, 144-51
Vilmorins, work of the, 143-54

Wahlbom, J. G., 19, 29

wheat, crossing, 113-16, 151-4;

crossing, technique of, 1 13-14,

115; dominance in, 116, 278-81;

Mendelian results w!th, 276-83 ;

see also Triticum
Wichura, Max Ernst, 178-83; list of

crosses, 180
Wiegmann, A. F., 160-4; estimate of

work, 164; list of crosses, 162
Wilson, John H., 275
winter-hardiness, inheritance of, 97,

142, 227, 267

Zea, crosses of, 157, 168, 171, 174-7,
329> 337, 338, 339, 349 ; experi-
ments with, 12-13, 68-70

zygomorphism, dominance of, 235 ;
in crossing, 208

LIST OF HYBRIDS BY GENERA OF THEIR PARENTAGES,

AND OF GENERA MADE THE SUBJECT

OF EXPERIMENT

Aegilops, 126, 127, 128, 129
Agave, 59

Agrosternma, 325, 329
Albuca, 275
Allium, 162
Anagallis, 206, 210
Althaea, 168
Alyssum, 142
Amaryllis, 142
Antholyza, 20
Antirrhinum, 41, 331
Aquilegia, 58, 168
Argemone, 41
Asclepias, 36

127, 128, 168, 235

Aster, 329
Antirrhinu7n,
Atropa, 210
Auricula, 66
Avena, 162
Azalea, lOO

Barharea, 142

Begonia, 275

Berberis, 58

Biscutella, 363

Brassica, 23, 122, 162, 210

Bryonia, 337

Bryanthus, 264, 266, 267

Calceolaria, 183
Carnellia, 138
Cannabis, 19, 20
Carduus, 271
Celtis, 142
Ceratonia, 71
Chamaerops, 70
Cheiranthus, 142
Chelidonium, 325, 329
Chrysanthemum, 329
Cistus, 58
citrus (lemon-orange), 135

Clarkia, 330
Coreopsis, 325, 329
Crinum, 97, ICXD
Cucurbita, 58, 121
Cucubalus, 161
Cypripedium, 265, 267
Cytisus, 138, 267, 268, 269

Dahlia, 155

Datisca, 21

Datura, 53, 58, 94, 130, 168, 194, 210.

325,330
Delphinium, 46, 48, 51, 52, 55, 56,

57, 62, 156, 162, 163, 168, 195, 264,

267
Digitalis, 94, 127, 168, 195, 206, 207,

259, 260, 262-3
Dianthus, 46, 48, 51, 52, 55, 56, 57,

62, 127, 156, 162, 168, 195, 264,

267, 272
Dipsacus, 60
Drosera, 272-5

Echium, 41
Epilobium, 41
Erica, 265-7
Ervum, 161, 162

Fuchsia, 168

Geranium, 142
Geum, 218, 267
Gladiolus, 168
Gloxinia, 142
Gypsophila, 53

Hedychium, 264, 266
Helianthus, 28
Hibiscus, 53, 60-1, 99
Hieracium, 22, 190, 211, 213, 218
Hippeastrum, 97, 100

374

LIST OF HYBRIDS

Humulus, 12
Hymenocallis, 98, lOO
Hyoscyamus, 41, 46, 32), 329
Hypericum, 38, 41, 168

Iris, 36

Jatropha, 21, 53

Ketmia, 38, 46, 50
Knautia, 60

Laburnum, 267

Lactuca, 23

Lapageria, 268-9, 270, 272

Lentiscus, 71

Leucojum, 46, 53

Lilium, 59, 337

Linaria, 127, 128

Linnaea, 60

Linum, 2 10

Lobelia, 94, 168, 194

Lupinus, 144

Lychnis, 161, 168, 190, 194, 325, 329,

363

Malva, 168

Masdevallia, 264, 267, 337. 338, 363

Matthiola, 46, 58, 168

Medicago, 156

Melandrium, 206, 339

Menziesia, 266

Mercurialis, 12

Mimulus, 227

Mirabilis, 20, 38, 53, 58, 126, 127,

208, 224, 338
Montbretia, 267
Musa, 24

Narcissus, 100

Nicotiana, 26, 36, 41, 43, 45, 46, 47,

48, 49, ?o, ?5, 94, 126, 127. 129,

162, 168, 186, 187, 206

Oenothera, 41, 168, 325, 329, 330, 332
Opuntia, 58
Orchis, 59
Origanum, 229

Paris, 38

Passiflora, 99, 275
Petunia, 126, 129, 136
Phaseolus, 162, 163, 210. 21 1. 212.
216-17, 218, 318, 337

Philageria, 264, 267, 268-9, 270

Philesia, 268-9, 270, 272

Phoenix, 11

Pistacia, 71, 74

Pisum, 87-91, 93, 102-3, 104-10, 151,
162, 171-4, 210, 211, 212, 214-15,
217, 218, 276, 29 1#., 335, 338,
340-1, 347, 349, 350, 352, 356.7

Polemonium, 41

Portulaca, 40

Primula, 126, 127, 168, 338

Prunella, 331

Prunus, 234

Pteris, 142

Raphanus, 122, 156, 206
Rhododendron, 99, 100, 141, 142,

264, 26?, 266
/^z'Z'i'j, 168, 267, 271, 275
/?^j^, 138
Rubus, 206

Salix, 180

Saponaria, 53

Sarracenia, 263-4

Saxifraga, 264, 267, 270, 271, 272

Sea bios a, 59

Scolopendrium, 143

Scrophularia, 41

5zWa, 58

.SxVfw^, 330, 331

Solanum, 325, 329

Spinacia, 12

Terebinthus, 71
Thalictrum, 28
Tragopogon, 22, 24, 43
Trifolium, 28, 325, 331
Triticum, 110-17, 277-282
Tritonia, 267
Tulipa, 65-6

Urtica, 19

Verbascum, 23, 24, 28, 46. 48, 51, 53,

54, 127, 128, 162, 168. 190
Verbena, 20, 22, 27
Veronica, 22, 24, 26, 27, 28, 325, 328,

.329
T'zW^, 161, 162
Viola, 329

z^a, 12, 157, 168, 171, 174-6,329,337,
338, 349

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