PLEASE HANDLE
WITH CARE

University of
Connecticut Libraries

3 1153 D155^773 S

Digitized by the Internet Archive

in 2011 with funding from

LYRASIS members and Sloan Foundation

http://www.archive.org/details/relationofcertaiOOeast

S
CONNECTICUT nOvl^?

AGEICDlieESL EXPERIMENT STillOIi

NEW^ HAVEN, CONN. •

BULLETIN 158, NOVEMBER, 1907.

The Relation of Certain Biological Principles
to Plant Breeding.

BY

EDWARD M. EAST, Ph.D.

The Bulletins of this Station are mailed free to citizens of Con-
necticut who apply for them, and to others as far as the editions
permit.

COSHECTICnT A&RICDLTnEAL EIPEBIMENT STATION,

BOARD OF CONTROL.
His Excellency, Rollin S. Woodruff, Ex officio, President.

Prof. H. W. Conn Middletown.

Prof. W. H. Brewer, Secretary New Haven.

B. W. Collins Meriden.

Charles M. Jarvis Berlin.

Edwin Hoyt New Canaan.

J. H. Webb Hamden.

E. H. Jenkins, Director and Treasurer New Haven.

STATION STAFF.

Chemists.

Analytical Laboratory.

John P. Street, M.S., Chemist in Charge.

E. Monroe Bailey, M.S. C. B. Morrison, B.S.

H. R. Stevens, B.S.

Laboratory for the Study of Proteids.

T. B. Osborne, Ph.D., Chemist in Charge. C. A. Brautlecht, Ph.B.

Botanist.
G. P. Clinton, S.D.

Entomologist.
W. E. Britton, Ph.D.

Assistant in Entomology.
B. H. Walden, B.Agr.

Forester.
Austin F. Hawes, M.F.

Agronomist.
Edward M. East, Ph.D.

Stenographers and Clerks.

Miss V. E. Cole.
Miss L. M. Brautlecht.
Miss E. B. Whittlesey.

In charge of Buildings and Grounds.
William Veitch.

Laboratory Helpers.

Hugo Lange.

c. d. hubbell.

Sampling Agent.
V. L. Churchill, New Haven.

TABLE OF CONTENTS.

Introduction.

I. The Evolution of Darwin and his Predecessors. 7

Lamarckism.

The theory — Its foundations — The meagre experimental
evidence — Modification due to environment — Temporary
inheritance of modifications — Weismann's theory.

Darwinism.

The Malthusian doctrine — Survival of the fittest — Evidences
of evolution — Organic relationship — Geographical distribu-
tion— Geological evidence — Comparative structures — Embry-
ological evidence — ^Variation under domestication — Sum-
mary— Post-Darwinian questions.

II. Later Evolutionary Theories and Principles. 20
Criticisms of Darwin's mechanical theory.

Variation — Classes of — Darwin's belief in evolution through
fluctuations — Early criticisms of this view — Recent criti-
cisms— De Vries' experimental evidence against — Evidence
of biometry against — ^Johannsen's work — Conclusion.
The mutation theory.

Introductory — Linnaeus' vs. Jordan's species — Elementary
species — Unit characters — The theory — The primrose experi-
ments— The chief points concerning mutations — Kinds of
mutations — Nature of mutation.

III. Heredity. 36
Introduction.

Blended inheritance.

Examples — Prepotency.
Mosaic inheritance.
Alternate inheritance and Mendelism.

Definition — Mendel — His experiments with a single pair of

characters — His results — His theory — Results with two pairs

of characters — General law — Conclusion.

IV. Methods of Plant Improvement. 45
Introduction — The three methods.

The selection of fluctuations.

The sugar beet — Maize breeding to change the composition
of the kernels — Inconstancy of races improved by fluctua-
tions— Propagating extreme fluctuations by asexual means.

4 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

Isolation of elementary species.

Le Couteur — Patrick Shirreff — Nilsson — Types found in
clover — What the types are — Distinctions between selecting
fluctuations and isolating elementary species — Judging plants
by their progeny — Correlated characters — Definitions — Ex-
amples— Nilsson's work — The Primus barley.

Improvement by hybridization.

Definition — Fairchild — Kolreuter — Reciprocal crosses —
Knight — Cause of variation — ^Knight-Darvvin law — Rela-
tionships and crosses — Prepotency of pollen — Later Men-
delian work — Morgan's hypothesis of germ cell dominance —
Bateson's presence and absence hypothesis — Masked char-
acters— Reversion — Heterozygotes — Practical applications of
Mendel's law — Conclusion.
V. Technique in Plant Breeding. T2>

Introduction.

Flowers and their parts.

Technique of hybridizing.

Sexual habits of the plant — maturity of the pollen —
Maturity of the stigma — Prevention of accidental pollina-
tion— Keeping pollen.

Technique of isolating elementary species.

Habits of the subject plants — The pedigree culture illus-
trated by red clover — Elementary species that have been
found.

Technique of maize breeding.

The problem — Early history — The row system — Standard
rows — Dangers of inbreeding — The Illinois system — Criti-
cism— The Ohio system — Criticism — A suggested method —
The theoretical foundation of methods.

Conclusion. 89

THE RELATION OP CERTAIN BIOLOGICAL PRINCIPLES
TO PLANT BREEDING.

By EDWARD M. EAST.

Introductiox

The recent stupendous progress in the experimental study of
variation, evolution and heredity has awakened greater interest
in the improvement of cultivated crops, for the theory of the
two studies must inevitably go together. Since the publication
of the Origin of Species in 1859, the questions involved have
been much at the mercy of the speculations of theorists ; and it
was seemiiigly forgotten that Darwin himself obtained much of
his evidence from domestic animals and cultivated plants. The
theorists were too busy in their debates to obtain many results
of practical value to the plant breeders; and the plant breeders
were obtaining so many surprising complications in their experi-
mental work, that the thought of the possibility of classifying
their thousands of observations under a few natural laws did
not occur to them.

The last decade has brought about a change of heart in the
two classes of workers, and a change in method in their work.
The student of natural evolution and the follower of changes
under domestication have recognized that they stand upon com-
mon ground, and as a result, the brilliant researches of a score
or more of recent investigators have made the prospects of gain
in the practical side almost too alluring.

For the plant breeder who can devote his whole time to the
study of his immediate problems, who will prepare himself by a
study of former investigations concerning variation and heredity,
and who will keep his ideas abreast of modern research, the
rewards indicated in some of the current journals are hardly
exaggerated. But for the busy farmer who wishes to know the
best methods of improving his general farm crops there is need
of caution in accepting the promise of results. Popular articles

6 CONNECTICUT EXPERIMENT STATION BULLETIN 158.

have been written of such roseate hue that large numbers of
men are quite ready to spend a portion of their time and money
in the improvement of their favorite crop. The general feeling
toward plant breeding is good and is certain to be productive
of valuable results; but it is not a subject from which to expect
great things without the study necessary for a general apprecia-
tion of its principles. Most certainly the writer does not wish
to discourage an increase in the number already interested in
plant breeding, but to encourage a greater study of its under-
lying principles and to have a rational view taken of our present
status of knowledge as to the possibilities which lie within the
application of these principles.

The prevalence of inadequate preparation for undertaking
special problems of practical plant breeding is partially due to
the unavailability of collected information on the subject. Com-
pilation in text-book form has not kept pace with the rapid
increase in results of research. There is disagreement as to
detail of method in the application of the few principles which
have been discovered and it is well that the prospective plant
breeder should consider these principles from various points of
view and draw his own conclusions.

There will be given in the following pages a short outline of
the current belief in the most important theories and principles
of variation, evolution and heredity, with their practical applica-
tion to methods of breeding farm crops, which it is hoped will
give the farmer an idea of the scope and present state of the
problems. Should the reader be sufficiently interested to pursue
the subject further^, he should consult the annotated list of
supplementary reading given at the end of this paper.

In the preparation of this paper, the writer has made free use
of the works of the following writers: — Bailey, Bateson, Biffen,
Castle, Correns, Darwin, Davenport, De Vries, Hurst, Johannsen,
Lock, Kellogg, Morgan, Pearson, Punnet, Romanes, Saunders,
Shirreff, Tschermak, Vernon, Webber, Weismann and others,
including our own government and experiment station workers.

EVOLUTION OF DARWIN AND HIS PREDECESSORS.

The Evolution of Darwin and his Predecessors.

Lamarckism.

The idea of organic evolution had germinated in the minds of
a number of deep thinkers from the time of Aristotle, and finally
bore fruit in the overwhelming evidence presented by Charles
Darwin in 1859. The adoption of the Jewish idea of the separate
creation of species by the Christian churches had almost stifled
early speculation. However, in the eighteenth and early nine-
teenth centuries, we find a more or less definite idea of the
production of species by the modification of their progenitors,
expressed by Erasmus Darwin, De Maillet, Goethe and Trevira-
nus. Lamarck had even developed a well rounded theory of evo-
lution through the inheritance of characters acquired during the
lives of individuals, a full half century before the time of Darwin.
The underlying thought of Lamarck's theory of the inheri-
tance of the effect of use and disuse may be seen in the example
which he himself first proposed in its favor. A bird, driven
through hunger to the water for food, will instinctively separate
its toes when they strike the water. The skin uniting the bases
of its toes will be stretched, in consequence. By the continuation
of this process, the descendants of such birds will develop the
broad membrane possessed by water birds such as ducks and
geese.

Lamarck's arguments may be given in a summary of his own
which is often quoted. He gives it as two laws of nature.
First law : "In every animal which has not finished its term of
development, the frequent and sustained use of any organ
strengthens and develops it and increases it in size proportionate
to the length of time it has been employed. On the other hand,
the continued lack of use of any organ gradually weakens it
until at last it disappears." Second law: "Nature preserves
everything she has caused the individual to acquire or lose
through the influence of the environment to which its race has
been for a long time exposed, and henpe the predominance or
loss of certain organs through use or disuse. She does this by
the production of new individuals which are endowed with the

8 CONNECTICUT EXPERIMENT STATION BULLETIN 153-

newly acquired organs, provided the acquired changes were
common to the two sexes of the individuals that produced the
new forms."

In other words, Lamarck has explained the diverse instances
of the survival of certain characters useful to the organism by
the theory that the need of such characters has caused their
necessary modification through the inheritance of such charac-
ters partially acquired or partially lost during the lifetime of
different separate individuals.

Since Darwin's time, the principles of Lamarck, with some
modifications, have received warm support by a large following
of eminent scholars, the so-called Neo-Lamarckian school, of
which Spencer, Cope, Eimer, Hyatt, Cunningham and Osborn
are a few of the well known writers who have collected data
in its support. It is noticeable that the best evidence has been
advanced by paleontologists, who have been deeply impressed by
the direct lines of evolution that geological evidence seems to
show has taken place. To their minds, the inheritance of
acquired characters must have taken place, to give a sufficient
explanation of these facts.

We can only say that while many of the facts seem to be
reasonably explained by the theory, the crucial point of the whole
thing, which is actual permanent inheritance of an acquired
character, has not been shown. It is true that this definite ques-
tion has been attacked by but few experiments, but in such experi-
ments the results have been negative. Successive generations of
mutilations, such as docked tails of horses, have never resulted
in a single case of undisputed inheritance. The idea that
previous fecundations have an effect upon succeeding progeny
of a mother has been shown to be without foundation. The
allied botanical phenomenon of zenia, as illustrated by the effect
during the current season of pollen of a black maize upon the
endosperm of a white variety, has been proved to have another
and a simple explanation. Thus we may go through the entire
list.

The one class of data that comes the nearest toward showing
inheritance of body acquirements, is that of the modifica-
tion of certain characters by the immediate influence of the
factors of environment, as food, light, heat, moisture, etc. In
many instances, where the environment of plants has been

EVOLUTION OF DARWIN AND HIS PREDECESSORS. 9

changed, there does indeed seem to be a temporary inheritance
of certain modifications. For instance, various grains have been
taken from their native plains and transplanted to mountains or
high plateaus. Among other minor changes that here have
taken place are earlier ripening and dwarfer forms. The com-
plete change of these characters does not take place in one gen-
eration, but in the course of three or four generations they
reach the limit of their modification. When these grains, after
several years cultivation on the mountains, are again resown on
the valley soil, they temporarily ripen earlier and remain more
dwarfish than their relatives that have been continuously culti-
vated in the valley. These characters, however, do not remain
permanent, but in a few generations the plants go back to their
former habits of growth.

Weismann has developed an elaborate theory tending to show
from a physiological standpoint that inheritance of acquired
characters is impossible. Every higher organism, both animals
and plants, is developed from a single cell, the fertilized egg.
Under circumstances favorable for growth this cell divides into
two equal portions ; and studies with the microscope have shown
that there is a very complicated mechanism which makes this
division exact and equal. By continuous divisions of this sort,
the adult body of every organism is formed. Some of the cells
which are formed, however, are modified in form and function,
and go to make up distinct Organs and tissues. But there are
cells which appear to have undergone no modification or change
whatever; these are the reproductive or germ cells of the body.
If we trace back to the original germ cell from which the
organism came, we see that each cell of the adult must have had
this germ cell for a common ancestor. Then since the repro-
ductive cells of this body are qualified to transmit all of its
minute characters, it is probable that they came from the parent
egg cell by a continuous "careful division ; and have received all
of its properties. The conclusion is that the inheritance of
qualities is transmitted from germ cell to germ cell in every race
of organisms and that the body is merely an offshoot, — a house
built up out of a part of the substance of the original germ cell
to shelter it until* it decays, and the germ cell is transmitted to
another house.

lO CONNECTICUT EXPERIMENT STATION BULLETIN I58.

It is clear then that any inherited variation must be a variation
which affects the germ cell, from Weismann's point of view ;
the use of a particular organ of the body would have no effect
upon it. There is no objection, however, to the belief that the
general health of the organism would affect the germ cells as
well as any other cells of the body. If the environment is excel-
lent for the bod)'^ development, then the germ cell should be well
nourished and able to produce a healthy body in the next genera-
tion if it has a fair chance, and vice versa. This theory would
readil)^ explain the apparent temporary inheritance in the case of
the plants transplanted from the plains to the mountains and
back.

There are evidently certain characters which are somewhat
modified by environment and which temporarily transmit these
modifications more or less perfectly; but for a variation to-be
permanently inherited, it seems probable, from both theory and
practice, that the germ cell must he affected structurally. It is
unlikely that a temporary "fattening" or "starving" of the germ
cell due to good or poor nourishment of the body, is sufficient
to produce a permanent change.

As a possible inheritance of acquired characters has such a
broad bearing upon plant-breeding questions, we must remember
when we come to their discussion, that as yet such permanent
inheritance is decidedly unproved. Moreover, such a conclusion
does not commit us to a belief in Weismann's ingenious but
unprovable theories. The plant breeder only wishes to know
that the relative probability of outside influences affecting the
structure of the germ cell and thereby making new characters
heritable — is extremely small.

Darwinism.
The great work of Darwin was influenced, if not suggested,
by an essay of Malthus on "Population"" published in 1798. Its
author gave incontrovertible ' evidence, by data f rorn countries
all over the world, that human population tends to increase by
geometrical ratio (that is, by multiplication) while food supply
tends to increase by arithmetrical ratio (that is, by addition).
This means that if human population were ftot kept down by
disease, war, famine and other checks, the increase would soon
outrun the food supply. As examples of similar but more rapid

EVOLUTION OF DARWIN AND HIS PREDECESSORS. II

increase may be cited many of the lower forms of animals,
which produce on the average one hundred eggs and reproduce
every week. If the entire progeny of a pair of such animals
were preserved living at the end of a year, their bulk zvotild
exceed the limits of the whole known universe.

This manner of increase is common to a greater or less degree
with all living organisms, both animals and plants; and since space
and food are not available for such increase, it follows that a
very large proportion of all individuals born must perish without
producing offspring. Darwin's idea was that out of all the
individuals coming into existence, some will show variations or
modifications in directions which adapt them better for the
environment in which they are placed than do the characters
possessed by their less fortunate brethren, and the former will
survive at the expense of the latter. This principle he called
Natural Selection, though later the more common term was that
of Herbert Spencer, the "survival of the fittest." Darwin's own
description of the process is this :

"If under changing conditions of life, organic beings present
individual differences in almost every part of their structure, and
this cannot be disputed; if there be, owing to their geometrical
rate of increase, a severe struggle for life at some age, season,
or year, and this certainly cannot be disputed ; then, considering
the" infinite complexity of the relations of all organic beings to
each other and to their conditions of life, causing an infinite
diversity in structure, constitution and habits — to be advanta-
geous to them ; it would be a most extraordinary fact \i no
variations had ever occurred useful to each being's welfare, in the
same manner as so many variations have occurred useful to man.
But if variations useful to any organic being do occur, assuredly
individuals thus characterized will have the best chance of being
preserved in the struggle for life ; and from the strong principle
of inheritance, these will tend to produce offspring similarly
characterized. This principle of preservation, or survival of the
fittest, I have called Natural Selection. It leads to the improve-
ment of each creature in relation to its organic and inorganic
conditions of life, and, consequently, in most cases, to what must
be regarded as an advance in organization. Nevertheless, low
and simple forms will long endure, if well fitted for their simple
conditions of life."

12 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

The very large amount of data that Darwin brought together
in support of his theory, fell naturally under several distinct
heads. It was all historical evidence in that it was made up of a
large number of facts collected from the different natural sciences,
which were most reasonably explained by assuming evolution to
be true. It neither satisfactorily explained how evolution took
place, that is, how small a variation would be preserved by
natural selection, nor did it show experimental evidence of the
actual production of natural species. It is difficult to pick out
from the mass of facts which Darwin had collected, particular
examples which are more illustrative than others, but we will
endeavor to give particular cases from each of the different lines.

Organic Relationship. At the lower end of both the animal
and vegetable kingdom, we find creatures of a very simple organi-
zation. They are living beings composed of one cell, and cannot
definitely be said to be either animals or plants. Moreover, these
organisms resemble in many ways the egg cell from which all
higher animals and plants originate. From these simple organ-
isms, we may follow up the two different and yet in many
respects similar lines of organisms which go to make up the
animal and vegetable kingdoms, until we reach, on the one hand,
man, and on the other, the complex flowering plants. The
gradation is noticeable in each line, although there are many large
gaps which are. not filled by any known organisms. The change
in the simplest case is by the addition of some single character,
though in most cases a number of characters are different
between the two nearest related kinds or species. First, there is
the addition of more cells and the single-celled organism becomes
(if we may speak with the definite idea of progress) a multi-
cellular organism. The simpler multicellular creatures have all
of their cells seemingly alike. Then comes the specializing of
different sets of cells to become tissues, and finally a multiplicity
of different tissues and organs useful for different needs and
performing different functions, form the higher plants and
animals with which we are more familiar.

Long before Darwin's time, it had been seen by different
naturalists that a study of the known animals and plants from
the simpler to the most complex showed related forms. Some
were evidently very closely related, that is they differed by very
few essential characters ; as an eagle and a hawk. Other types

EVOLUTION OF DARWIN AND HIS PREDECESSORS. 1 3

were very far apart, as an oyster and a dog; and yet there are
a number of similar attributes possessed by both the oyster and
the dog. They both digest food, possess voluntary and involun-
tary muscles and have circulatory systems.

The natural result of such study was to show that the plant
and animal kingdoms could be compared to a great tree, which
had branched at the root into two large trunks, each of which is
divided into many branches. The animal trunk, for instance, has
one great branch of fishes and another great branch of birds.
From these great branches come smaller branches and twigs of
closer and closer relationship as to characters. The whole
arrangement seems to show the development of more complex
from less complex beings.

Geographical Distribution. In working out this tree of rela-
tionships, it has been shown that groups of closely connected
creatures are often found living in small districts, and that when
a natural barrier, as an ocean or a lofty mountain range, is
passed, the^-e is found largely a new fauna and flora. Of course
there are types of both animals and plants that exist over large
areas, but in most cases they are species able to migrate freely
and are adapted to the differences in environment that have been
encountered. Some species live in numerous small areas:, the
mountain hare, for instance, exists from the Arctic regions over
the greater part of Europe in the spots where there are mountain
ranges or climates cold enough to suit its requirements. It is a
natural explanation of these facts to suppose that the moun-
tain hare had a continuous range over Europe during the
last glacial epoch when the European climate was much as the
present Arctic climate. But when the climate of Europe gradu-
ally became temperate, the hare was able to exist only on certain
mountain ranges corresponding in climate to the Arctic regions.
The flora of the high mountain ranges also is essentially
Arctic in all of its general characters, and yet the species are not
the same as those found in the Arctic regions. It is not rational
to suppose that new species were separately created upon different
mountain ranges after the formation of the present climate in
the temperate zone, and yet are so closely allied to Arctic species
as to be included in the same germs.

Finally, it has been shown that the number of species indig-
enous to isolated islands is proportional to their biological isola-

14 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

tion from other larger or older islands. By biological isolation
is meant not only distance in miles, but also freedom from pre-
vailing winds or ocean currents from other lands. The nearer
islands are to continents, the closer related are their fauna and
flora. As far as is known there is no exception to this law.

Geological Evidence. When Darwin's theory was first pub-
lished, there was much criticism concerning the gaps existing in
the 'family tree' of the animal and the vegetable kingdom. Espe-
cially was there a lack of types possessing structures which would
show them to be links between the larger families and orders of
animals and plants. It is on this point that modern study of
the science of the classification of animal and plant remains found
in the dififerent strata of rocks, which we call paleontology, has
produced such valuable evidence. These remains of ancient ani-
mals or plants which we call fossils have naturally been confined
to their hard parts such as bones and teeth, which have been the
more easily preserved. However, from such remains as were
available, large numbers of these primitive types have been dis-
covered and described. In America has been found a long line
of remarkable progenitors of the horse, leading back to an animal
the size of a dog, with four separate toes to each fore-leg and
three to each hind-leg. More striking still, in the earliest known
bird, the Archaeopteryx, the similarity to a reptile is easily seen.
The tail is very long, with twenty-one separate joints, every
joint bearing a feather upon each side. In the modern bird, the
tail joints are very much fewer in number, short and enlarged,
and bear long tail feathers in a fan shape, forming the so-called
tail. This shortening up of the tail did not come at once but is
seen in all gradations in fossil birds of later periods.

In point of time the geological evidence is found to be exactly
in conformation with the theory. The earlier remains are those
of less speciaUzed forms, while the remains found in strata of
rocks of later ages are of more specialized or higher forms. The
record shows that of the vertebrate animals, the first to appear
were fishes, followed successively by amphibians, reptiles, birds
and mammals. However, because mammals arose later than
birds, we do not need to conclude that mammals arose from birds,
or even from our present form of reptiles. Probably there was
a diverse evolution from some early amphibians which gave rise
to reptiles, birds and mammals.

EVOLUTION OF DARWIN AND HIS PREDECESSORS. 1 5

Geological evidence alone is not necessarily conclusive, for
many fossil forms represent the highest development of extinct
types, and hence are not progenitors of yet higher types ; but
as yet there are no data among fossils that is directly against the
theory of evolution.

Comparative Structures. The evidence of geology and that of
classification is based largely upon the study of comparative
structures, for the external appearance of organisms is often
deceiving. We must get beyond the superficial points and study
, the more permanent characters. As an example, the porpoise
is a fish-like animal, its teeth being more fish-like than mammal-
like; but on the other hand, it suckles its young. Is it then a
fish or a mammal? A mammal most assuredly, for teeth are
very variable organs, while suckling the young is characteristic
of the whole class of mammals and of them alone.

The evidence of comparative structures is divided into two
parts, that of the change of organs to become better fitted for
different kinds of work, or more useful under different conditions
of life, and that of the tenacity with which organs which are now
functionless, remain.

Returning to the porpoise and its relative the whale, it must
be inferred from the whole structure of these animals that their
progenitors were terrestrial quadrupeds of some kind which for
some reason became aquatic in their habits. Such a change of
life made it desirable for the animals to possess characters more
fish-like. Probably such changes first took place in the most
variable parts, such as the skin, claws and teeth. Then, as time
went on, the modifications extended to more typical structures,
until the whole shape of the body was affected by the bones and
muscles becoming better adapted for aquatic than for terrestrial
locomotion. We see in seals the stage where the hind legs are
thrown backward until they are of little use on land, but serve to
form a kind of double fish-like tail. In the whale the modifica-
tion has gone still further: the visible signs of posterior limbs
have entirely disappeared, but there still remains within the body
the bones of a rudimentary pelvis with indications of bones of the
hind limbs. The fore-arm also, which looks externally very like
a fin, still retains, in a modified form, all of the mammalian bones
of the fore-arm, wrist and hand, so that the general appearance of
the skeleton of these parts bears a strong resemblance to that of
3

1 6 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

the fore-arm of man. Moreover, the head, although modified
until it resembles that of a fish, still retains all of the bones of the
mammalian skull.

Such adaptations to fit conditions of life are very general in
both animal and plant life. Plant adaptations are largely modi-
fications to make sure of fertilization and consequently of very
definite use to the species in continuing its existence. A com-
mon example noticed by everyone is the very great amount of
pollen produced by maize, which is wind-pollinated, with neces-
sarily a great loss. Compare this with the small amount of
pollen produced by the pea, which by its structure is assured
of self-polHnation. Moreover, there are thousands of examples
of wonderful modifications* by which plants secure animal aid in
their fertilization, — such as showy blossoms, secretion of nectar,
and modified shapes of corollas which assure pollination by the
insects that come to the blossoms for nectar.

The amount of evidence showing that once useful but now
functionless organs often persist when their existence is not
harmful to the organism, is not so large as that of which we
have just been speaking. But certain vestigial organs still
remain in man which are interesting evidences of his part in the
system of evolution, and of his close relation to the animals to
which he feels superior. The tenacious grasp of the young
infant and the extreme natural inflection of the feet is very
reminiscent of the monkey family. The muscles of the external
ear which are large and of use in quadrupeds, are still retained
by man in a small and functionless condition. The absence of
a tail in man is popul|irly supposed to be a final argument against
his quadrumanous descent. But this is exactly what we should
expect, for tails have been done away with in man's nearest
relatives, the anthropoid apes. Man, however, as well as the
apes, retains a few rudimentary caudal vertebrae at the end of his
sacrum and even vestigial tail muscles are present in some
adults. Finally may be mentioned the vermiform appendix,
which in its reduced size is useless to man, and even is harmful
in some cases as being the seat of appendicitis. In herbivorous
animals the organ is of large size and functions in the process
of digestion. Some such heritages are present in all classes of
animals and plants and serve as particularly incontrovertible
evidence of the relationships of different types.

EVOLUTION OF DARWIN AND HIS PREDECESSORS. 1 7

Emhryological Evidence. Embryology is that branch of
biology that deals with the formation and early development of
organisms. Such great advances in the science have been made
since the time of Darwin, that many evolutionists have regarded
it as giving the principal evidence to the theory.

Without going into technical detail, the evolutionary proofs of
embryology might be largely summed up in the following sen-
tence. The early development of any organism partially recapit-
ulates the embryonic history of its race formation. This does
not mean that there are' not many gaps in the process ; but this
expresses the general tendency of development. As an example,
young salamanders before birth are found to be furnished with
gills; and if they are taken from their mothers shortly before
birth, the gills are able to perform their functions, and the
young salamanders can respire in water which would drown
their own mothers. The complete formation of gills in the
embryo salamander is an entire waste of time, as the gills are
never of use in the normally developed young. It is clear, then,
that one could only expect such a phenomenon to happen from
the viewpoint of a previous evolution.

In man himself there are stages in the development of the
embryo when it is scarcely distinguishable from the embryos
of any of the other vertebrates, such as fish, amphibians, rep-
tiles, birds or lower animals. It early possesses the two-cham-
bered heart of the fish, and gill slits of undeveloped gills.
Further on in its development, the embryonic heart has the three
chambers characteristic of amphibians and finally the four-
chambered heart characteristic of the double circulation of birds
and mammals.

Variation under Domestication. In the study of the varied
forms of our domestic animals and cultivated plants, Darwin
found a great deal of his best data regarding the variability of
organisms. He showed that particularly among domestic
animals, for example the pigeons, there are varieties descended
from a common wild ancestor, which if met with in a state of
nature would be classed as different species and possibly as
different genera. There is no reason to believe that animals in
the wild state are not just as variable as domestic animals,
although man undoubtedly selects and perpetuates variations
which would not be of sufficient value to the organism to survive

1 8 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

by natural selection. However, proof of such variation of
characters of specific rank is proof enough that sometimes there
must occur variations which are sufficiently useful to protect their
possessors in the struggle for existence that we saw is con-
tinually taking place in nature.

Such in brief were the lines of argument brought together by
Darwin in support of his evolution theory; and with such bril-
liancy and with so man}^ data did he maintain it that before his
death practically the whole thinking world was converted from
the orthodox Jewish belief in the special creation of every
species, to that of the development of all organisms from very
primitive types.

To summarize the whole question, we may state just what
were the fundamental points which Darwin proved. The over-
whelming amount of his historical data, as we have seen, left
no reason to doubt that there had been an organic evolution.
In order for a natural organic evolution to have taken place there
must have been three cooperative factors : first, variability within
species ; second, a capacity among organisms for transmitting
particular characters ; and third, a means of selection of varia-
tions for perpetuation.

Many examples of sufficient variability were easily found
among existing data, though it is true they were generally con-
fined to domestic animals and plants ; and there was no reason to
doubt that certain variations of sufficient specific character had
been inherited under man's selection. As to his natural selec-
tion factor, it was unquestionably shown that there was and is a
struggle for existence in which the greater part of all organisms
coming into being, perish. Variations sufficiently of advantage to
their possessors, to make their attaining adult life and reproduc-
ing their kind relatively more probable, would obviously survive.
These facts will stand forever as a sufficient monument to the
memory of Darwin.

The questions to which he did not give a sufficient answer are :
first. What is the physiological meaning of the different kinds of
variation? second, how great must a variation be to be selected,
or how often must it occur to have stability? third, what is the
rate of inheritance of different kinds of variation? fourth, what
is the mechanism of inheritance? and fifth, must only favorable

EVOLUTION OF DARWIN AND HIS PREDECESSORS. 1 9

variations be selected or will variations which are simply non-
injurious survive? In other words, Darwin proved the fact of
evolution and established one of its great working principles, but
left to the future to largely explain its detailed mechanism.

The criticisms of Darwin's work are many and a large number
of them are very just, but they do not affect the truth of general
Organic Evolution. Huxley well expressed the facts when he
said: "Even if the Darwinian hypothesis were swept away,
evolution would still stand where it is." The criticisms that are
at all pertinent concern the five questions just given. Other
criticisms are largely due to a misunderstanding of Darwin's
own work. His work was so broad that he himself fairly
stated a large number of the criticisms that were brought to bear
upon it. He recognized that the detail of the manner in which
evolution took place was yet almost untouched by investigation.
Yet in many of these issues the problems were outlined by the
hand of a master.

It is odd, at first thought, that all of the important criticisms
are of primary and direct importance to plant breeding; yet it
really is not odd, for the factors in the improvement of crops
are the same as those of a natural evolution. There are the same ^
classes of variations to deal with, the same questions of inherit-
ance of these variations. It is true that artificial selection takes
the place of natural selection, but also here it is imf)ortant to know
in each case whether the laws of inheritance are such that a
single useful variation which has occurred, can be preserved, or
if it must be lost by intercrossing with individuals not possessing
the variation.

In the next chapter, we deal with some of the points of evolu-
tionary criticism which have affected our entire conception of
the methods to be used in plant breeding.

20 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

II.

Later Evolutionary Theories and Principles.
Criticisms of Darwin's Mechanical Theory.

There are two main classes of variations, both of which Darwin
recognized as agents in the work of evolution. The first he
called "fortuitous" or chance variations, although he admits that
this is an incorrect expression which serves only to plainly
acknowledge our ignorance of the exact cause or causes of each
particular variation. This is the common type of variation seen
in every growing plant and animal. It is now called fluctuating
variation, and each individual variation a fluctuation, — terms
which we shall henceforth use. Illustrations of fluctuating varia-
tion are found in every character of all living organisms ; which
is the same as saying that no two plants or animals are exactly
alike. Take as an example a number of ears of maize. They
may be of the same variety, have grown on the same soil, and
have had exactly the same treatment during the growing season ;
nevertheless they differ among themselves in length, in circum-
ference, in weight, in number of rows, in fact in every character
we may pick out.

The second class of variations are those which Darwin called
"definite" or discontinuous variations. To this kind of variation
belong those characters that suddenly appear in their perfection,
capable of transmitting the new feature with only the ordinary
amount of fluctuating variation. These variations are now
called mutations. To illustrate our meaning take the peach tree.
It is not an uncommon thing for one branch to bear those smooth-
skinned fruits called nectarines. This is mutation,* which con-
tinues constant from year to year. The nectarines, however,
differ among themselves in size, weight, amount of flesh and
other characters. In other words, they still have fluctuating
variations among themselves. Galton illustrates the point of
distinction nicely by use of a polyhedron, — an object with a num-
ber of equal sides. Suppose some force rocks the polyhedron as

* Some writers refuse to recognize bud mutations as real mutations, but
as bud mutations are sometimes transmitted by seed, there seems to be no
reason for their exclusion until a definite scientific distinction between
them and germ mutations is known.

LATER EVOLUTIONARY THEORIES AND PRINCIPLES. 21

it rests upon one of its faces. It will rock back and forth but
always tends to come to rest upon this face. These oscillations
represent fluctuating variation. But should a sudden shock rock
the object so violently that it finally comes to rest on another of
its faces, we might think of it as a mutation.*

Darwin believed that evolution and the changes in domestic
animals and plants were very largely the result of the selection
of the small individual variations or fluctuations, as the following
quotation shows : —

"It may be doubted whether sudden and considerable devia-
tions of structure such as we occasionally see in our domestic
productions, more especially with plants, are ever permanently
propagated in a state of nature. Almost every part of every
organic being is so beautifully related to its complex conditions
of life that it seems as improbable that any part should have been
suddenly produced perfect, as that a complex machine should
have been invented by man in a perfect state. ... If mon-
strous forms of this kind ever do appear in a state of nature
[he was speaking of a pig which had been born with a short pro-
boscis, E. M. E.] and are capable of reproduction (which is not
always the case), as they occur rarely and singly, their preserva-
tion would depend on unusually favorable circumstances. They
would, also, during the first and succeeding generations, cross
with the ordinary form, and thus their abnormal character would
almost inevitably be lost."

It is only fair to say that Darwin changed his views slightly
in the last edition of his work. So many examples of, mutations
had come under his notice that he could not disregard them
entirely, and he says : "In the earlier editions of this worl? I
underrated, as it now seems probable, the frequency and impor-
tance of modifications due to spontaneous [mutations] variability.
But it is impossible to attribute to this cause the innumerable
structures which are so well adapted to the habits of life of each
species."

We shall see later from the work of De Vries that mutations
do not necessarily occur singly, and from the work of Mendel,,
that they would not need to be swamped by intercrossing; but

* De Vries believes fluctuations are confined to plus or minus variations
of the same character; that is, "linear" variations. Mutations, on the
other hand, may take place in any direction.

2 2 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

we will now take up some of the earlier criticisms of Darwin's
views that are particularly related to the part played by fluctua-
tions and mutations in evolution,

A great obstacle toward explaining- all adaptive structures by
the use of natural selection is the fact that many structures
which are useful in a fully developed state must have been use-
less in the beginning when rudimentary and undeveloped. This
criticism has been made by all opponents of the theory, but was
stated with particular force by the Duke of Argyll. He argues
that if an organ . was developed gradually and very slowly, it
follows as a matter of course that every beginning of such an
organ must have been functionless at first. "No structure can
be selected by utility in the struggle for existence until it has
not only been produced, but has been so far perfected as to
actually be used." For example, the eye of animals or the wing
of birds, he thinks, could not have been of sufficient use to the
possessors of their first rudiments to have caused them to have
been selected. Romanes, in replying to this criticism, thinks that
even if only rudimentary as eye or wing, they may have been
useful for other purposes. A nerve ending may have been sensi-
tive in a slight degree to light, and thus have enabled the animal
to find more food or to hide itself better from its enemies. Like-
wise a rudimentary wing might not have been useful for flight
but still have served for more rapid locomotion. These explana-
tions, while ingenious, seem to be rather strained and make us
feel as if we should rather have some theory which does not put
too great a burden on our faith.

Morgan has put forth an objection belonging to this same class
which is even more pertinent. Many species of animals have
the power to regenerate, or grow again, certain parts of the body,
when lost by accident. It is absurd to think of natural selection
as preserving an individual which has this power in a very slight
and imperfect manner, and by a continued selection of those
individuals that can better regenerate lost parts, — finally perfect-
ing this power. It has been shown experimentally that only a
small per cent, of the animals of a species possessing this power
ever lose a limb or other part. What chance would they have of
surviving by natural selection in competition with numerous
perfect, healthy specimens? The only possible explanation of
the perfecting of such a power by the selection of small fluctuat-

LATER EVOLUTIONARY THEORIES AND PRINCIPLES. 23

ing variations is that they might be dependent upon other varia-
tions in structure which were useful when rudimentary. We
know that sometimes seemingly independent structures do go
together in an unaccountable manner, a phenomenon which is
called correlated variation. But here again, such an explana-
tion is as unsatisfactory support as is a straw to a drowning man.

There are at least four important objections among early
criticism which cannot admit explanation by the natural selection
theory alone : — first, that a large proportion of the characters that
distinguish species from each other are seemingly useless and
therefore cannot be explained by a use selection; second, the
most common of specific characters, sterility between species,
Darwin himself showed could not be explained by natural
selection ; third, the swamping effects of free intercrossing would
render impossible by natural selection any evolution of species in
divergent lines ;* fourth, many characters useless for the preserva-
tion of individuals have been developed by only one sex of a given
species. In the latter class belong the beautiful plumage
developed by many male birds. Darwin has developed a theory
supplementary to natural selection, that he calls sexual selection,
to account for such cases. In brief, it is that higher animals do
not mate at random but exercise an instinctive choice in obtaining
their nuptial partners. The female cardinal or redbird, for
example, has had an instinctive liking for a scarlet color. In the
early history of the species, males were accepted as mates by the
females only when they possessed certain red markings that had
appeared as variations upon the plumage of certain individuals.
These particular males were sires of the greater part of the next
generation, and thus impressed upon it a large amount of their
characteristics. A continuation of this process is thought to have
produced the characteristic coat of the male of the species. Why
only the males of some species possess certain characters to the
exclusion of the females, our present knowledge of heredity
ofifers no explanation. Sexual selection seems a reasonable
explanation for the evolution of a few characters belonging to this
class, but it, like natural selection, has been given more and
broader phenomena to explain than it can possibly cover.

These earlier criticisms conclusively show that the natural
selection theory is mainly, as Morgan states, a theory of adaptation

*See Mendel's work for an explanation of this objection.
.4

24 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

to environment. It is a sieve which sifts out variations which
have appeared that are of prime utility to the organism or to the
species. It is not a cause of evokition itself, but a working
agent for destroying organisms less fit for their station in life than
some of their relatives or species less fit for existence than others.
It is not a selective agency, but a rejective agency. It is plainly
evident that it is one of the great factors of evolution, possibly
the greatest factor; but it is as plainly evident, even with the
added theory of sexual selection, that numerous characters pos-
sessed by living organisms must have developed without its
agency.

We will next mention the more recent criticisms of Darwin's
theory, which have to do with the probability of evolution having
taken place through the selection of fluctuating variations. Lord
Kelvin has furnished the first telling obstacle by his calculations
of the age of the earth. Earlier geologists and biologists, when
they had once turned away from the idea that the earth was only
about six thousand years old, allowed themselves to suggest
millions of millions of years as the amount of time necessary for
the geological changes and those of evolution to have taken place.
These ideas in turn were forced to give way when Lord Kelvin
calculated the earth's age upon definite physical data. His cal-
culations were divided into three sets : first, based upon the rate
of the earth's rotation as affected by the retardation of the tides ;
second, based upon the rate of cooling of the earth, calculated
from the rate at which the temperature increases on boring
inward toward its centre ; third, based upon the rate of cooling of
the sun by radiation. There was a noteworthy agreement in
these three calculations, all tending to show that less than one
hundred million years has elapsed since the earth's surface has
been in a condition to support life. These calculations have been
somewhat changed since the discovery of the immense amount of
energy stored up in radioactive substances, yet it still remains
necessary to conclude that life has not flourished on this planet
a sufficient length of time to have developed our present fauna
and flora solely by the selection of fluctuating variations.

De Vries has attacked the question of the probability of evolu-
tion through the selection of fluctuations from another point, that
of their inheritance. He believes that fluctuations are a kind of
acquired characters; at least that they depend solely upon the

LATER EVOLUTIONARY THEORIES AND PRINCIPLES. 25

effect of food, light, temperature, moisture and other factors of
environment. Nevertheless, they are, in a certain degree,
inherited. There is nothing unusual in this when we consider
that all higher organisms are but collections of cells each with its
own purpose to fulfill. Should the environment of an individual
be particularly favorable so that its general health is above the
average, then might not the reproductive cells be better nourished
and they therefore be enabled to produce better organisms, owing
to their better start in life? We should expect, however, that
such improvement would not be permanent, but would cease if the
selection of such individuals was abandoned, and even degenerate
to the original type. This is exactly what has been found both in
historical cases and in experiments. The improvement of sugar
beets in their sugar content has now been in progress for about
fifty years, yet the maximum improvement was obtained in a
very few years after the start, and now all that continued selec-
tion of the highest fluctuations of sugar content can do is to keep
the average up to the point to which it had been raised years ago.
As an experiment upon this point, De Vries tried to raise the
average number of rows of a variety of maize by selection. This
variety had an average of 13 rows per ear. As we know, no
ears of maize have an odd number of rows, but the average was
between 12 and 14 rows per ear; The actual number of rows in
individual cases varied between 8 and 22. He planted an ear
having 16 rows and in the crop found a new average of 15 rows
per ear. From this crop some good ears bearing 20 rows were
planted, and this process of selection was continued annually for
six seasons. At the end of this time the average of the variety
had reached 20 rows. The lowest number on any ear was then
12 and the highest found was 28, a number which he had never
seen in the regular variety. There are two points to be con-
sidered in this experiment, as De Vries points out. The first is :
Could this average of 20 rows have been obtained in one year?
On examining the results of the different years it was found that
an average increase was obtained equal to two-fifths of the
deviation of the parent ear from the average. An average of
20 rows per ear is a deviation of 7 from the average of
the original variety of 13 rows per ear. Then if 7 equal two-
fifths of the deviation, to obtain an average deviation of 7 in the
progeny, we should need a deviation of 17^ rows above the

26 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

average 13 rows; that is, a selected ear containing 30-32 rows.
Two hundred ears had been examined originally and one 22-
rowed ear was found. Now by the mathematics of probability,
we can predict that by doubling the number of ears examined
we would expect to find one ear with one more row, or 23 rows.
This means that by the examination of 100,000* ears, he would
have had the same likelihood of finding an ear of 32 rows as he
had of finding the ear of 22 rows when he examined the two
hundred.

The point is this: By examining 100,000 ears he could prob-
ably have found and planted an ear containing 32 rows and
would have obtained his race of corn averaging 20 rows to the
ear in one season. But by taking six years for the selection,
he was able to obtain the 20-rowed race by the use of only
about 1,000 plants. Hence the gradual change that takes place
in the t3^pe of a selected fluctuating character is apparent rather
than real, and is due to the rejection and non-propagation
during the breeding of so many numbers below the selection
standard.

The second important point is : Does an average, such as
De Vries obtained for his corn after six years selection, remain
constant ? To test this point De Vries allowed the 20-rowed
race to propagate indiscriminately and found that in only three
or four years the old type of 13-rowed corn was reached.
A number of other instances could be cited that indicate that all
races improved by the selection of fluctuating variations are
inconstant and tend to return to their original type. This con-
clusion is perfectly in accord with the conclusion we reached in
the last chapter regarding acquired characters.

These conclusions of De Vries regarding the inconstancy of
races improved by selection of fluctuations, have in the main been
confirmed by an entirely different school of investigators called
biometricians. Biometry is the science of applying mathematical
methods of dealing with statistics to biological problems. It is
not necessary for us to go into their technical methods, but we
must give two of their important discoveries, whose derivation
it is not necessary to understand to appreciate their value.

* There is necessarily a physical limit in the production of rows in ears
of maize, as in all other natural productions. Above this limit mathe-
matical calculation is valueless.

LATER EVOLUTIONARY THEORIES AND PRINCIPLES.

27

The first is called Quetelet's law. Quetelet, a Belgian astrono-
mer about the middle of the last century, discovered that the
relative frequency of the occurrence of fluctuating variations in
living organisms obeys the mathematical theory of probability;
that is, it is just what we should expect if the number of
causes combining to make fluctuations in nature is infinitely
large. For example, we measured the lengths of a hundred and
eighty-six ears of a certain variety of corn and found that they
fell into classes of one inch in the following manner.

Length in inches
Frequenc)'^

314
o|i

6 1 7 I 8 1 g I 10 I n I 12 I 13 I 14
5 I 19 I 37 I 58 I 40 I 18 I 6 I I I o

Now if we draw a horizontal line and divide it into equal parts
marked with these classes of one inch each ; then erect per-
pendiculars at each point proportional in height to the number of

4 5 6 7 8 9 10 " It 13

Fig. I. Frequency polygon or curve of variation in length of maize ears

ears found in each class; by joining the tops of these perpen-
diculars we get a close approximation to what the mathema-
ticians call the normal curve. By knowing this fact, we can
predict approximately how many ears of a certain length we
should find in one thousand ears of this variety.

The second great law of the biometricians is called the law
of ancestral heredity. It was enunciated by Galton but received
modification and confirmatory data from Pearson. In its present
form, it supposes that the average resemblance of this offspring
to the two parents is 50 per cent., to the four grand-

2 8 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

parents 25 per cent., and to the eight great-grandparents 12.5
per cent, and so on.*

Assuming the truth of the law of ancestral heredity, and a
perfectly normal distribution of fluctuations, Pearson has shown
what could be accomplished by continued selection, provided all
biological data followed the laws that he has found in his data
from measurements of the human race. The conclusions were
derived from measurements of several different characters, but
the following will serve as an imaginary example to illustrate his
results. If the average height of the population were five feet
and six inches, and individuals six feet high were selected as
parents, then in the first generation he has found that the average

M

Fig. 2. Normal curve

Compare with Fig. i.

height of the offspring would be five feet six inches plus 62 per
cent, of six inches, which is the deviation of the parents from
the average. Again selecting six-foot parents, the height of the
offspring would be five feet six inches plus 82 per cent, of six
inches, and in the third generation five feet six inches plus 89
per cent, of six inches. Selection of six-foot parents for a large
number of generations would only bring the average up to five
feet six inches plus 92 per cent of six inches. This shoyvs that

* This law has been much misunderstood, and a great deal of criticism
of it has arisen through the activities of the Mendelian school of biologists.
If we consider a single character possessed by the organism, it may be
generally untrue, but if we consider all of the thousands of characters
possessed by the organism, it certainly approximates the truth.

LATER EVOLUTIONARY THEORIES AND PRINCIPLES. 29

in three or four generations the offspring may have an average
of 90 per cent, of the selected character, but after this selection
has only little effect. Moreover, Pearson showed that if selec-
tion was stopped at any time and the offspring allowed to inbreed,
they quickly returned toward the average of the selected character
in the original race.

Recently some tentative conclusions of Johannsen's, from
experiments upon barley and kidney beans, may be interpreted
as agreeing with Weismann's theory, and De Vries' and Pear-
son's conclusions, — that fluctuating characters have almost noth-
ing to do in the permanent improvement of a race. All of his
experiments were made upon plants which could be self- fertilized
during successive generations. In this way he made the experi-
ment simpler than he could have done if he had used different
plants for the two parents. All of the descendants of a single
plant, arising by self-fertilization, he speaks of as a 'pure line.'
The characters used were typical fluctuating characters such as
the weight of the seeds. All members of a pure line showed
normal fluctuations around a mean or type value. Moreover, all
seeds from plants of the same variety, made up of a number of
such pure lines, also showed a normal variability. In the pure
lines, some of the mean or type values were very close to the
mean of the variety in general, while others were quite different,
being both lower and higher than the general mean value. When
any individual, differing widely from the mean value of its pure
line, was selected for propagation, its offspring showed a regres-
sion or tendency to go back toward the type of its particular line;
but showed no regression to the mean value of the variety.

It is quite clear if these conclusions are warranted, that the only
improvement that selection can effect is towards the isolation
of one of these pure lines and must of a necessity come to an
end when the pure line is entirely isolated. The difficulty of
doing this in practical work is obviously very great because of
natural intercrossing. It was the opinion of Darwin that by
selection the type of the race would be raised and a new selection
possible from the extremes in fluctuation of this new type. This
would set no limit to the amount of improvement that could b§
made. The experiments of De Vries and Pearson, however, and
the experience of breeders in general as illustrated by the case of
the sugar beet seem to agree with Johannsen's theory, that such

30 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

is not the case. Johannsen's work, however, indicates that the
complete isolation of a pure line would give a strain which would
not regress to the mean of the original mixed population, but
would breed true to its own type. This is contrary to the general
belief of breeders, and his further results will be awaited with
great interest;

The results of our considerations of the criticism of Darwin's
theory, that evolution must take place through natural selection
or some kindred eliminating agency as sexual selection of minute
fluctuating variations, have led to three general conclusions^^
First, natural selection will not explain either the evolving of
many characters that could not have been useful in a rudimentary
state, or the large numbers of characters that appear to be entirely
useless to organisms. Second, the age of the earth since the
formation of oceans, as calculated by physicists, does not allow
sufficient time for the evolution of higher plants and animals by
the selection of minute fluctuating variations. Third, experi-
mental evidence from several diverse lines all tends to show that
a selection of fluctuating variations can make no permanent
improvement, and that there is a narrow limit to the changes that
can be made, even with' their continuous selection.

The Mutation Theory.

The study of evidence relating to the points that have just
been discussed, has resulted in a waning belief in the efficiency
of fluctuating variations to explain the facts of evolution,
and in a growing belief in the prominent part played by
discontinuous variations or mutations. We owe to Hugo De Vries,
an eminent Dutch botanist, the largest amount of data regard-
ing mutations, and even the word itself when used in this sense.
It is true, other prominent workers were beginning to trace out
similar theories, and particularly important experiments had been
conducted by the distinguished English zoologist, Bateson ; but
when De Vries' investigations were published the time was ripe for
their general appreciation.

The data from which De Vries evolved his theory is thought to
%how not only that mutations are a class of variations useful as a
factor in evolution, but that they are the only possible way by
which evolution could take place. Whether this is true or npt
is not possible at present to determine; but we can say that

LATER EVOLUTIONARY THEORIES AND PRINCIPLES. 3 1

the rapidly increasing volume of data points toward this conclu-
sion. Moreover, there is no experimental data at hand to refute
this view. The mutation theory certainly does clear up many of
the points which did not seem to be clearly explained from Dar-
win's point of view. We will endeavor to give an outline of the
chief points involved.

In the middle of the eighteenth century, Linnaeus, the great
Swedish botanist, introduced our present system of classifying
plants and animals. He used two names : a species name or name
of a group of individuals which were fairly constant and alike
in their characters and which differed from other related groups
by characters which could be recognized from descriptions ; and a
generic name which included related groups of these species in
a broader class called a genus. He supposed that his species
were the units of nature and were created as such in the begin-
ning. He did recognize subdivisions of species which he called
varieties but had no very clear ideas concerning them. The
object of his work was to bring into some order the plants then
known, and not to study lesser divisions.

The classifying of species has since been more or less a series
'of individual judgments of different botanists; some used more
definite characters as distinctions between species, and made a
small number of species, while others used fewer or smaller dis-
tinctions and described four or five times as many species in the
same genus.

More recently Jordan, a French botanist, became satisfied that
the only reasonable way to classify species was to grow a large
number of individuals and study the characteristic differences
between them. When this was done, he found that while some
of Linnaeus' species were relatively uniform, others contained
many groups of plants which differed from each other by one or
more constant characters. Often these differences were in parts
of the plant which would remain unnoticed by the untrained eye,
but still the differences were there and were transmitted to the
succeeding generations.

De Vries has called these groups of plants, "elementary species."
His idea is that plants and animals are made up of thousands of
large or small, but distinct heritable characters ; and that these
characters have arisen, one or more at a time, fully formed and
able to function, from parents which did not possess the characters.
5

32 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

It is recognized that some plants are much more variable in this
respect than others : the common whitlow grass (Draba verna)
has had several hundred of these elementary species described,
while others of Linnaeus' species seem to vary only with the
common fluctuating variation. This phenomenon is explained by
the hypothesis that there are periods when a species is producing
mutations and other periods when mutations very rarely if ever
appear. These periods may be hundreds of years apart and thus
account for the apparent constancy of some species such as wheat,
of which we have a long history under domestication.

In making culture studies of many species of plants, these
elementary species have been found very common indeed, but
no one -had seen a new form originate from an older wild one
until De Vries had the good fortune. It is true that many wide
mutations, or jumps of a distinct kind, had been isolated among
cultivated plants, and were called "sports" by horticulturists.
De Vries, however, discovered and propagated a series of interest-
ing mutations from a plant growing wild on some fields near
Amsterdam.

The plant which was caught in the act of originating a new
species is an American plant of the evening primrose family
known as CEnothera Lamarkiana. It had been cultivated in Hol-
land many years but had escaped from cultivation and had been
growing wild for a long time. On closely examining these plants,
De Vries discovered two new and unknown forms that were
quite unlike the remainder of the plants which were typical of
the species. Each of these types occurred in spots, as if they
had arisen as the offspring of a single plant. Fortunately,
De Vries was not satisfied with the single observation, but took
seed and roots of a number of the plants of each type and grew
them in his garden for a number of generations. In all, he
cultivated at least 50,000 plants, and among this number about
800 were found which differed distinctly from the parent species,
and whose characters were constant when reproduced by self-
fertilization. That is, he was able to obtain from one to three
per cent, of new and distinct forms which did not tend to go back
to the parent form but to remain constant. One of the forms
was a giant form with large flowers ; one was a dwarf form ; in
one the ovules were imperfect; and another had defective pollen.
The last two forms were evidently less fitted for existence than
the parent form and were raised with difficulty, while other

LATER EVOLUTIONARY THEORIES AND PRINCIPLES. ;i^

forms were able to survive in natural competition with the
parent species.

These new forms corresponded to the elementary species that
had been observed before in nature, but had' never been seen to
arise. Each character had the common fluctuating variability
which often made the fluctuation of two forms overlap, for
instance the longest leaves of the short form being longer than
the shortest leaves of the long form. But in each of these cases,
Avhen the two forms were cultivated separately, the variability was
found to group itself around a typical point and to be distinct in
each form.

We cannot go deeply into the numerous questions regarding
variability and inheritance upon which these experiments have
shown light, but it may be well to sum up some of the chief points.

1. Mutations are not so rare as was formerly supposed. They
are found in wild as well as cultivated plants. Their occurrence
reasonably accounts for the numerous "elementary species," or
subdivisions of Linnaeus' species that are found in nature.

2. Mutations are constant in succeeding generations and thus
account for the constancy in nature of these elementary species.
The tendency of the progeny of extreme fluctuating variations to
return to the original type appears to make continuous evolu-
tion impossible, but with mutations which remain constant until
succeeded by other mutations, there is no such difficulty.

3. The criticism that imperfect and rudimentary characters
would not survive by natural selection, is here valueless, for
mutations appear fully formed.

4. Anticipating the text a little, we may state that Mendel's
work on heredity has shown that mutations would not neces-
sarily be swamped by intercrossing with the parent kind, even
if they occurred singly. It may also be deduced from his work
that useless characters may survive.

5. De Vries' work shows that in the working of the principle
of natural selection, it is more likely a contest in which the
fittest elementary species survives. The contest for survival
among individuals due to fluctuating variations has not yet been
shown to produce permanent changes. Possibly this would be
done, however, if we imagine a gradually but permanently chang-
ing environment to which individual organisms adapt themselves
in different degrees.

34 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

6. By mutations, it is believed that evolution may have been
accomplished in the time allotted for its action by the calculations
of the physicists and geologists.

From this discussion we can see that whether or not we accept
De Vries' theory as proven* in its entirety ; nevertheless as a
theory it explains reasonably and clearly the majority of the perti-
nent criticisms of the theory of evolution by the selection of
fluctuating variations, which were given at the end of the first
chapter.

According to De Vries, there are three classes of mutations,
progressive, degressive and retrogressive. If an entirely new
character appears in an organism, it is a progressive mutation.
It is thought that this class has been the great factor in evolu-
tion. The degressive mutations are those which occur when a
character appears that has been partially latentf or hidden.
A retrogressive mutation is when a character previously active
becomes latent, as when a species that has always produced
colored flowers suddenly produces a white variety.

A mutation is held to be the appearance or disappearance of a
distinct heritable character. De Vries disclaims any idea that
these changes must be wide, but they must be distinct in that there
in a change of type in the variation which is inherited. The
mutation may be within the limits of a fluctuation, but still be a
true mutation. To illustrate this, cut-leaved plants of a number
of species have appeared as mutations, but there may be individual
leaves of the ordinary types which have as deep or deeper
incisions through fluctuating variations than have the least incised
individuals of the cut-leaved type. It has been customary to
regard mutations as sufficiently definite changes in botanical
characters that they may be recognized when grown in pedigree

* There are points concerning the germ cell structure of De Vries'
primrose mutations, and the fact that certain of these aberrant forms
have continued to give off mutations, that make it a question if these
cultures were not either hybrid forms, or parthenogenetic forms (forms
in which the seeds develop without fertilization). The original wild
plant seems to have disappeared in America, hence experiments with it
to determine these points cannot be made. Nevertheless, even if the
primrose mutations should be otherwise explained, it would not affect
the general theory of the discontinuity of heritable characters. Other
data presented by Bateson, De Vries and others, are more convincing
to my mind, than are the primrose experiments ; although the latter
have been received with greater popular acclaim.

t Latent is a term used to explain the condition of a character that
appears to be lost, but is only obscured or hidden.

LATER EVOLUTIONARY THEORIES AND PRINCIPLES. 35

cultures ; that is when isolated and reproduced in pure lines for
several generations. Doubtless with sufficiently accurate methods
this could always be done. But it does not seem to be a necessary
part of the theory to regard mutations as additions or subtrac-
tions of what are generally regarded as specific characters. If
mutations may appear in any direction, I see no reason why they
may not sometimes appear as linear changes (plus or minus) of
characters already present. Johannsen's results might then be
interpreted as mutations in which the real unit characters are
portions or segments of what visibly appears as the character, but
differing from fluctuations of the same character by the constancy
with which they are reproduced. A perfectly isolated line con-
taining only a definite number of segments of the character in
their germ cells, would remain true to its own type in succeeding
generations of progeny. The difficulty in isolating a pure line is
that the fluctuations of different lines overlap and are indistin-
guishable in appearance.

If we regard the growing sugar beet as containing a chemical
laboratory for the manufacture of sugar, we may imagine
changes taking place in the germ cells from which an apparatus
and reagents appear by which a higher or lower amount of sugar
would normally be produced. But grouped about this normal type
would be fluctuating variations due to environment. In other
words, there might be germinal or genetic variations of the
sugar-producing character, a pure line from which would nor-
mally produce beets with 12 per cent, sugar, but with fluctuating
variations of from 10 per cent, to 14 per cent, sugar. Another
pure line might normally produce 10 per cent, sugar with fluc-
tuations of from 8 per cent, to 12 per cent.

36 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

III.

Heredity.

Through common usage, the term heredity brings to our minds
a more or less definite meaning, but a precise definition is diffi-
cult. Suppose we say that it is the tendency of the characters of
blood relations toward duplication. Variation, which we have
just been discussing, and heredity are in one sense opposite in
their meaning. If nothing interfered, and inheritance were
perfect, there would be no variation and hence no evolution;
differences in species would necessarily be due to direct creation,
or spontaneous generation, and each species would be made up
of individuals exactly alike. On the other hand, we could
hardly imagine the chaos if there were no limits to variation.
Heredity and variation have been spoken of as two opposed
forces, the first a centripetal force which is striving to keep
nature fixed within due bounds, and the second a centrifugal
force which is continually striving to overleap these bounds.
The continued working of these two forces under laws of which
we as yet know little, has built up the organic world which
surrounds us.

Blended Inheritance.

Of the mechanism of bisexual inheritance very little is known,
but from observation of its results it has been divided into
blended, mosaic and alternate inheritance. Blended inheritance
is where there is a fusion of two characters, so that a character
possessed by an offspring appears to be an average of the two
characters as possessed by the parents. The most familiar case
of blended inheritance is the mulatto — the result of the union
of a white an-d a black individual of the human race. The
mulatto is intermediate between the two colors, and breeds true
for generation after generation. If the mulatto is crossed again
with white or black stock, the resulting offspring is correspond-
ingly whiter or blacker.

Cases of blended inheritance are found in all sorts of crosses,—
those between races, varieties and elementary species. It has
been thought to be a characteristic occurrence in hybridization
between different Linnean species, but it is now known that even
here the other forms of inheritance occur. No general law for

HEREDITY. 37

the mechanism of blended inheritance has been found, but Gal-
ton's law of ancestral inheritances as mentioned in the last chap-
ter gives the expectation of average ancestral resemblance in
the different generations. This law is thought to apply especially
to blended inheritance, but there is no reason why it could not
apply to all forms of inheritance if we consider the total sum of
characters of an individual and not a single character.

It is particularly in blended inheritance that the phenomenon
of prepotency* has been noticed. This is the tendency of one of
the parents of a cross to have more of its characters reproduced
than would be normally expected. It is stated that in the .pro-
duction of the mule the characters of the ass are prepotent, while
in crosses between the dog and the jackal the latter is prepotent.
It is variously stated that iti crossing plants, the characters of
the older species are prepotent, and that progressive mutations
are prepotent. Accepting the mutation theory of evolution as
true, these two statements are in direct opposition to each other.
We should be cautious about accepting any theories concerning
prepotency until we know more about the subject.

Mosaic hiheritance.
The most familiar example of mosaic inheritance is where
animals of different coat colors are bred together. We some-
times get an individual that is piebald. The characteristic colors
of the two parents are inherited by the offspring in patches on
different parts of the body. These spotted races have originated
among almost all of our domestic animals and are noticeable in
many of our flowering plants. In some cases they may be muta-
tions that breed true, as is believed by Cuenot, but it is most
generally thought that this is only a special form of alternate
inheritance and that it will be explained later on that basis.

Alternate Inheritance and Mendelism.
It is upon alternate inheritance that results of greatest value
have been obtained. By this term are designated numerous cases
in which a character of. one parent is inherited, apparently to the
complete exclusion of any influence of the other parent on this
character. Data now being obtained by investigators indicate
that this exclusion is sometimes an exclusion of appearance and

* It may be that prepotency will later be explained as due entirely to
dominance of characters. (See Mendelian Inheritance.)

38 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

function, and that the alternate character may yet appear in sub-
sequent progeny under certain conditions. The classical example
of this type of inheritance is that of eye color in the human race.
It is a matter of common observation that the offspring from a
union of a brown-eyed parent and a blue-eyed parent is never a
mixture or blend of the two ; the children are either brown-eyed
or blue-eyed like one or the other of the parents. Until 1900
this type of inheritance was thought to be comparatively rare. In
that year, however, it was discovered by workers in heredity in
three different parts of the world, that two laws of the utmost
importance to both science and practice had been buried in the
oblivion of an unnoticed journal for a whole generation. These
laws are now known as Mendel's laws.

Gregor Johann Mendel was an Austrian priest, a teacher of
physics and natural science in the Cloister at Briinn. He was
appointed Abbot at Briinn, about 1869, and unfortunately for
science he had little time left from his executive duties for the
pursuance of his studies. He died in 1884 practically unknown to
the world. It was not until sixteen years after his death that
it became widely known that in 1865 he had reported a paper
giving results of ten years' expifcriments on inheritance, — results
that were fundamental and epoch making.

By a wonderful foresight, he perceived that if progress was
to be made in the study of heredity the problem must be simplified
as much as possible. It was the simplicity of his experiments that
crowned them with success. There were two things especially
necessary to be controlled, namely, accidental mixtures due to
crossing, and differences in too many characters. The common
garden pea fulfilled these demands. It could be self-fertilized
generation after generation without deterioration, and varieties
were found that differed from each other in but few characters.
Mendel selected varieties of the pea which differed from each
other in such characters as "round or wrinkled seeds," "yellow or
green cotyledons" or seed leaves, and "purple or white flowers."
These varieties he found to be true to their characters by inbreed-
ing. He then crossed them once and made careful records
of their progeny when inbred for a number of succeeding
generations.

He crossed a yellow seeded variety with pollen from a green
seeded variety, and again crossed the green seeded variety with
pollen from that bearing yellow, seeds. It was found that it made

HEREDITY. 39

no difference which variety was used as the pollen parent and
♦ which as the seed parent, the seeds resulting from the cross were
in every case yellow. He called the yellow color the dominant
color and the green color the recessive because it had receded from
sight for a time.

These yellow seeds were planted the next season and the blos-
soms were allowed to self-fertilize, that is, pollen from the
stamens of a flower was allowed to fertilize the pistils of the
same flower. It was found that all of the plants bore both
yellow and green seeds, frequently both colors being found in the
same pod. This proved that although the seeds from the cross
were in the first generation all yellow in color, the green color
was still there potentially, waiting to appear in the next
generation. Continuing the work for the third generation, he
found that all of the plants from green seeds, when allowed to
self-fertilize, produced green seeds entirely. This was continued
for six generations with no reapipearance of the yellow character.
In other words, the recessive character bred true.

When the same method of inbreeding was used on the yellow
seeded progeny of the gross, however, a different result was
obtained. Some of the plants were found, when self-fertilized,
to produce both yellow and green seeds just as their parents had
done, while others bred true in succeeding generations. That
is, some of these yellow seeds were "pure" yellow seeds, while
others were "hybrid" yellow seeds like the parents. But in the
case of the hybrid yellow seeds, the yellow color was still
dominant; that is, it was apparent to the eye; while the green
color was recessive or hidden. Moreover, long continued experi-
ments showed that there was a constant numerical ratio between
the yellow and green seeds, which is illustrated by the following
table.

yellow X green (or vice versa)
ist gen. all yellow

I
2d gen. 75^ yellow to 25^ green

\ I

3d gen. 2S% 50^ 25^ f

pure yellow to hybrid yellow to pure green pure green

4th gen. pure yellow 25^ 50^ 25^ pure green pure green

^ pure hybrid — pure -^ '-^

pure yellow yellow yellow green pure green pure green
6

40 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

His results may be stated as follows :

If two contrasted characters which have previously bred true
are crossed, one only, the dominant character, appears in the
hybrid. (The Law of Dominance.)

Second, in succeeding g-enerations, self-fertilized plants grown
from seeds of this cross reproduce both characters in the pro-
portion o"f three of the dominant character to one of the recessive
character. Furthermore, the recessive character continues ever
after to breed true, whiTe those plants bearing the dominant char-
acter are one-third pure dominants which ever after breed true to
the dominant character, and two-thirds hybrid dominants which
contain the recessive character in a hidden condition. (Mendel's
law of inheritance.) Using D to represent the" dominant charac-
ter and R to represent the recessive character, the working of the
law may be thus illustrated:

D R

\ ./

^^^ DR ^\\
D-" /- I I \-^« \R

° r /f i\ ^ ^\

D D D DR R R R

Mendel did not claim that this law of inheritance holds good
for all organisms or even for all plants, but it is now being cor-
roborated for an ever increasing number of characters in both
plants and animals. Even the results which he obtained did not
follow the exact numerical ratio just given but were sufficiently
exact for him to formulate a theory to account for the observed
facts.

The theory supposes that when a dominant and a recessive
character meet in a cross, the germ cells which are produced
in the hybrid do not blend these characters but possess either the
one or the other ; and as the possession of either character is a
matter of chance, on the average 50 per cent, of the germ cells
will bear the dominant character and 50 per cent, will bear the
recessive character. In a plant, for example, 50 per cent, of the -
pollen cells would bear the "dominant and the other 50 per cent,
would boar the recessive character. The t.g% cells would like-
wise one-half contain the dominant character and one-half the
recessive character.

HEREDITY. 4 1

Now if we could pick out at random any one hundred pollen or
male cells to fertilize any one hundred egg or female cells, we
can see that there are equal chances for four results. A D male
cell might meet a D female cell, a D male cell an R female cell,
an R male cell a D female cell, and an R male cell an R female
cell. In an abbreviated form it amounts to this :

D-

-^D

Male

D^

^D

Female

cells

R--

^\ R

cells

R-

-^R

We have (D + D), (0 + R), (R + D) and (R + R) formed
in equal quantities, but as the two middle terms are the same, we
can reduce the formula to one (D -)- D) to two (D -f- R) to one
(R-|- R). But wherever there is a D present in the germ cell,
the dominant character shows while the recessive character is
hidden. The one part or the 25 per cent, of the individuals
showing the character (D -f- D) will appear to be just like the two
parts or 50 per cent, of the individuals having the character
(D -|- R). Therefore there will be 75 per cent, of the individuals
which will show the dominant or D character while 25 per cent,
will show the recessive or R character. These 25 per cent, show-
ing the R character will ever after breed true because they contain
nothing but' the recessive character, while of the 75 per cent,
showing the dominant character, one-third or those having the
pure (D -^ D) character will breed true in succeeding genera-
tions while the other two-thirds having the (D -j- R) or hybrid
character will again split in the next generation.

Of course it is only theoretically that these ratios are exact.
They increase in accuracy with larger numbers. If one thousand
seeds were counted in the second generation, they would come
nearer the proportion of three to one (3D to iR) than if one
hundred were counted. As a tangible illustration of what may
be expected in practical work, take one hundred black beans and
one hundred white beans and shake them up in a hat. Now draw
them out in pairs, and see what combinations you 'get. In an
actual count I obtained the following results.

Actual
number

Theoretics
number

22

55
23

2 black

•I black, I white

2 white

25
50
25

42 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

This explains why the practical work is not in exact accord
with the theory. The actual results approach nearer and nearer
to the theory as larger and larger numbers are used.

Mendel was not content with experiments in which only one pair
of differentiating characters were concerned. He made crosses
in which two and three pairs of characters were associated and
found that they independently obeyed the same laws. Taking two
pairs of characters, he designates the dominant characters as A
and B and the recessive characters as a and b. The characters
crossed were as follows :

Seed parent ) A form round Pollen parent j , „„ji^ ^ „i

A o ■{ D J 1 r 1 11 u i o seed-leaf color

AB I D seed-leaf color yellow ab i

{ ^ ( green

When these two forms were crossed all of the hybrid seeds

appeared round and yellow (AB) like those of the seed parent,

that is, the round and yellow forms were dominant.

When these seeds were sown and the plants self- fertilized, four

kinds of seeds appeared in the four combinations that were

possible ; and with the following numbers of each :

AB round and yellow 31S

aB angular and yellow loi

Ab round and green 108

ab angular and green . .' 32

These figures stand approximately in the relation of 9AB to

3Ab to 3aB to lab : but these forms which appeared to be of

only four classes were found in the next generation to be made

up of nine really different classes.

From the round yellow seeds (apparently AB) were obtained:

(i) AB round and yellow seeds 38

(2) ABb round yellow and green seeds 65

(3) AaB round yellow and angular seeds 60

(4) AaBb round yellow and green, angular yellow and green seeds 138

From the round and green seeds (apparently Ab) were
obtained :

(5) Ab round green seeds 35

(6) Aab round angular and green seeds 67

From the angular and yellow seeds (apparently aB) were
obtained :

(7) aB angular and yellow seeds 28

(8) aBb angular and yellow green seeds 67

From the angular and green seeds (ab) were obtained:

(9) ab angular and green seeds 30

HEREDITY.

43

We notice that there were nine classes of individuals produced
whose characters had the formulae given above. This was
experimentally proved. The forms AB, Ab, aB and ab were
found to be true and did not afterwards vary. The hybrid
character of the remaining classes was subsequently shown.

The numerical relations found were approximately the following
series. AB, Ab, aB, ab, 2ABb, 2aBb, 2Aab, 2AaB and 4AaBb.
This is really a combination by multiplication of the two series, —

(A + 2Aa + a)x(B + 2Bb + b) = AB + Ab + aB + ab +

2ABb + 2aBb + 2Aab + 2 AaB + 4AaBb.*

The two pairs of characters behave independently of each other
and as if chance only governed their combinations. Moreover,
three pairs of contrasted characters were found to behave in
exactly the same manner, the number of forms found being what
would theoretically be expected if the above product were multi-
plied by another series represented by C -f- 2Cc + c.

These results can be reduced to still simpler terms, as is shown
in the following table. Let n represent ttie number of pairs of
contrasted characters in the parents. When they are crossed,
the second generation, when self-fertilized, show visible differ-
ences of 2 to the nth power. These visibly different classes
actually contain 3 to the wth power different classes, the phe-
nomenon of dominance obscurity part of them. Finally when
crossing to secure combinations of n characters, we must have 4
to the nth power number of individuals to be theoretically certain
of at least one individual in each class.

Mendel's Law of Inheritance of Unit Characters.

No. of pairs of dif.
between parents.

n

No. of visibly dif.

classes each cont. one

pure individual.

2"

No. of actual classes,
both pure and hybrid.

3"'

Smallest No. of offspring

allowing at least one

to a class.

4"'

I
2

3

4
5
6

2

4

8

16
32
64

3

9

27

81
243
729

-, Experimen-
7 1 tally tested
g° [ by Mendel
^■' for peas.
256]
1024 y Calculated
4096 J

* Instead of writing AA and aa in the series one of the letters is
dropped. t

44 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

When such a noteworthy set of conclusions as, those of Mendel's
is announced it is important that they should be confirmed by
other investigators. This has been done by investigators in
several countries, and in recent years Mendel's laws have been
found to hold for a large number of characters in numerous
varieties of our domestic plants and animals. Characters in such
different subjects as rats, mice, guinea pigs, cats, horses, oxen,
poultry and various insects, among animals ; and for wheat, oats,
maize, peas, beans, etc., among plants have shown Mendelian
inheritance in certain characters in hybrids between their varieties.
How far these laws will be found to hold, we do not know at
present; but the number of cases is being extended daily. It is
possible and even probable that a great many cases which are now
considered as blended and mosaic inheritance will be found to
obey some extension of Mendel's law ; when it is better under-
stood, moreover, it is quite likely that many characters that are
now regarded as units will be finally divided into several units,
and their behavior in different combinations thus accounted for.
Bateson has already found that several characters, such as certain
colors, which would at first thought be regarded as unit char-
acters, are actually made up of two, three or even a larger number
of factors ; and such facts make it very difficult to derive con-
clusions from experimental data on account of their very great
complication. #

We have treated Mendelism rather more fully than blended or
mosaic inheritance because it is the only law of inheritance that
has been formulated that will greatly help the plant breeder.
Galton's law of ancestral inheritance, even though it should
finally be brought into conformity with Mendelian results, will
probably never be of great practical use because it will be much
more of a law of averages within races than a law of expecta-
tion from crosses.* ' Mendelism has been treated in this chapter
just as the author himself left it. In the next chapter some of
the more important modern results along Mendelian lines will
be described.

* Galton's law is statistical and deals with averages; Mendel's law is
physiological and deals with individuals.

METHODS OF PLANT IMPROVEMENT. 45

IV.

Methods of Plant Improvement.

We have tried to show that there are three main methods by
which the numerous improvements in our cultivated plants and
domestic animals have been effected. They are:

1. The continued selection of individuals whose desirable
characters have fluctuated above the average of their race.

2. The isolation, from natural mixtures of several elementary
species, of those forms which possess the most desirable economic
qualities.

3. The combination of desirable qualities possessed by dif-
ferent related forms, by means of hybridization.

The most progressive plant breeders use all three methods ; but
these methods must be modified to meet the various peculiarities
of different kinds of plants. Sometimes free intercrossing or a
tendency toward sterility in inbred plants almost prohibits the
complete isolation of natural forms. In some cases the common
method of propagation is by buds, and fluctuations can be multi-
plied in a commercial way. In other plants desirable characters*
are possessed by different types, and hybridization must be used to
determine if certain combinations of characters will not produce
the desired quality.

We cannot take up any extended history of what has been done
in plant breeding, for that would be to give the history of each
of the thousands of varieties of our cultivated plants ; but we will
give a number of typical examples, illustrating what has been
accomplished by the use of these three lines of work. The
investigations along theoretical lines have shown that there are
obstacles and limitations belonging to each class. It is necessary
to know how these facts affect practical work

The Selection of Fluctuations.

We have already mentioned the sugar beet as an example of a
crop in which fluctuating variations have been selected for a long
term of years. We do not know just how much progress was
made, if any, irl raising the sugar content of the sugar beet
previous to the middle of the nineteenth century. The beginning

46 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

of its culture for sugar purposes was about the year eighteen
hundred. Experiments were carried on in both Germany and
France, and even with the very imperfect methods of the time,
6 per cent, of sugar was often obtained. What the fluctuations
in sugar content of individual beets were at that time we do not
know, for modern and accurate methods of sugar determinations
in beets have been in use only for a generation. Previous to
the time of Louis Vilmorin, about 1850, there had been some
few selections of mother beets for higher sugar content by plac-
ing the roots in solutions of different density and selecting those
having the highest specific gravity. There was probably little
improvement made in this manner, for the frequent formation
of hollows in the centre of the root introduces large errors in such
determinations. Louis Vilmorin recognized the fault in this
method and began the first real selection of mother beets for
higher sugar content by pressing out the juice from a section of
the beet, making density or specific gravity determinations upon
the juice itself and planting the mother beets whose superiority
was thus shown.

Later the improvement of chemical methods of analysis, includ-
ing the use of the polariscope, has made rapid determinations of
sugar possible. At present there are German and French seed
growers that make as many as 100,000 sugar determinations upon
individual beets ever year. Their method is to take a cylindrical
piece cut from the beet in a diagonal. In this way a fair sample
is taken, for different cross sections of the roots vary in their
sugar content. After these cylinders from all of the beets are
analyzed, the best are selected and are carefully saved until next
season, when they are planted to produce seed for the commercial
growers.

As early as 1878, the time of the Paris Exhibition, we have
records of varietiesithat averaged 16 per cent, to 18 per cent, sugar
and whose individual beets ran as high as 25 to 28 per cent.
Since that time thirty years of continuous selection has made no
progress. Our commercial beet races are kept up to about 16
per cent, by annual selections from large numbers of mothers
of known composition, but it is impossible to reach a higher
average. The fluctuations are practically the ^same as we find
in our earliest records. Apparently no mutations have intervened,

METHODS OF PLANT IMPROVEMENT. 47

and the best strains of belts have been fairly well isolated. Now
all that selection is doing- is to perpetuate these improved
races. Beets are open fertilized, that is, they cross-fertilize
naturally in the field, hence the continuous need of careful selec-
tion to keep their sugar content up to the standard reached a
generation ago. It has been definitely shown that without tliis
continuous selection their constant intercrossing with inferior
blood that still remains, will immediately make them regress
toward the old average of sugar content of a hundred years past.
Possibly there are causes contributory to this regression, but it
can hardly be doubted that they would reach this average in a
very few years if selection ceased.

Work analogous to raising the sugar content of the sugar beet
has been going on in this country for the past ten years. - I refer
to the work of Hopkins and his associates at the Illinois
Agricultural Experiment Station in changing the composition of
the maize kernel. With this work the writer had the pleasure
to have been connected for five years.

Work was started in 1896 to change the composition of the
maize kernel along four different lines, for higher and lower
protein, and for higher and lower oil contents. One hundred
sixty- three individual ears of Burr's White maize from the 1896
crop were analyzed and the proper selections in each case planted
in their respective plots. In each plot from twelve to twenty-four
rows were planted and each row contained only the kernels from
a single ear. In succeeding years, a hundred or more ears were
analyzed from each breeding plot and those ears from the "High
Protein Plot" which showed the highest per cent, protein were
saved to plant the next year's "High Protein Plot," while those
ears from the "Low' Protein Plot" which showed the lowest
per cent, protein were saved to plant the "Low Protein Plot" of
the next season. Like methods were followed in the "High Oil"
and "Low Oil" breeding plots.

The results of the "High Protein" and "Low Protein" plots
for ten generations are shown in the following table.

We have here a concrete illustration of what was done in ten
years ; but we must not get from it the idea that this average
increase or decrease of protein in a variety of white maize obtained
in ten years is a measure of what would be obtained by the
selection of any other fluctuation in any other plant. This is

CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

Results of Selection for Increase and DIcrease of Protein in Maize
AT the Illinois Agricultural Experiment Station.*

High Protein Plot.
Average in per cent.

Low Protein Plot
Average in per cent. '

Year.

Seed planted.

Crop.

Seed planted.

Crop.

between the
crops, per cent.

1896
1897
1898

1899
1900
I9OI
1902
1903
1904
1905
1906

12.54
12.49
13.06

13-74
1478
15-39
14-30
15-39
16.77
16.30

10.92
II. 10

11.05
11.46

12.33
14.12

12.34

13-04

. 14-98

14-72

14.26

8.96
9.06
8.45
8.08
7.58
8.15
6.93
7.00
7.09
7.21
1

10.92

10.55

10.55

9.86

9-34
10.05
8.22
8.62
9.27
8.57
8.64

0

-55
•50
1.60
2.99
4.07
4.12
4-42
5-71
6.15
5.62

what was obtained under the soil and cHmatic conditions at
Urbana, Illinois, during a certain period of ten years, when about
(in most cases) one hundred ears were analyzed and, on an
average, the proper, best twenty fluctuations planted. The
amount of average change that can be made will vary with the
number of individuals considered and with the strictness of selec-
tion. If one thousand ears had been analyzed each year and only
five of these planted, the same results would have been obtained
in a much shorter time. There are also environmental conditions,
such as moisture, light and available plant food of the proper kind,
that would undoubtedly influence the results. Moreover, in
other characters and in other plants the variability of the variety
would affect the progress that could be made.

The next table gives the results that -were obtained in the
"High Oil" and "Low Oil" plots from the same variety of maize
with about the same rigidity of selection.

Here we see an illustration of the point just men,tioned : the
percentage changes in oil content, when referred to the total oil
contents of the crops are much greater than the changes that took
place in the proteids in the same amount of time.

* The figures for the following three tables have been furnished
through the courtesy of Dr. L. H. Smith, Assistant Professor of Plant
Breeding at the University of Illinois.

METHODS OF PLANT IMPROVEMENT.

49

Results of Selection for Increase and Decrease of Oil in Maize at
THE Illinois Agricultural Experiment Station.

High Oil Plot.

Low Oil Plot.

Aver, in per cent.

Aver, in

per cent.

Differences

Year.

crops, per cent.

Seed planted.

Crop.

Seed planted.

Crop.

1896

4.70

4.70

0

1897

5.39

4.73

4-03

4.06

.67

1898

5.20

5.15

3-65

3-99

1. 16

1899

6.15

5.64

3-47

3.82

1.82

1900

6.30

6.12

3-33

3.57

2.55

I9OI

6.77

6.09

2.93

3.43

2.60

1902

6.95

6.41

3.00

3.02

3.39

1903

6.73

6.50

2.62

2.97

3-53

1904

7.16

6.97

2.80

2.89

4.08

1905

7.89

7.29

2.67

2.58

4.71

1906

7.86

7-37

j 2.20

2.66

4.71

There are given in the next table the extremes of fluctuation in
the ears analyzed for protein each season. It is noticeable that
several years of selection passed before certain extremes appeared,
as, for instance, the high proteid ear containing 15.71 per cent,
protein that appeared in the year 1900. It would be easy to cal-
culate the number of ears that must have been analyzed the first
year in order to have had the same relative probability of finding
an ear containing this amount of protein, as there was of obtain-
ing the ear with 13.87 per cent, protein which was found in that
year. Could there have been a sufficient number of ears exam-
ined and the proper number planted, there is a great probability
that these averages obtained in the crops after ten years' breeding
might have been obtained in one or two years. In fact, we may
note here that at this station an ear of the Longfellow variety
whose ancestry had been unselected was found, in which the
protein content was 16.2 per cent., which shows that nature is
producing quite high extremes if we can but find them.

But there is a point still more important. We can see in the
next table that there is evidently a limit to the fluctuations in
protein or oil. The record-breaking ears — those with extremes
of composition greater than had been obtained before are fewer
in later years and the extreme is not pushed up or down to any
considerable extent. It seems evident tliat the isolation of the
extreme lines is fast being accomplished, if indeed it has not
already been done. The curve of crop averages given below will

50 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

Fluctuations in Protein Content of Individual Ears.

High Protein Plot.

Low Protein Plot.

Year.

No. Ears
analyzed.

Minimum.

Maximum.

No. Ears
analyzed.

Minimum.

Maximum.

1896
1897
1898
1899
1900
I9OI
1902
1903
1904
I9OS
1906

163
112
252
216
216
60
90
100
100
120
120

8.25
8.34
7.72
7.71
10.31
8.94

9-54

8.47

10.61

it).77

10.46

13-87
13.62
14.92
14.78
15-71
16.12
15.01

17-33
17-79
17-39
17-67

163
48
126
144
144
126
90
100
100
120
120

8.25
8.22
7-50

6.66
7.08
7.54
6.37
6.38
6.13
6.62
6.49

13-87
13.98
16.08
13.06
12.29
1305
969
10.20
10.46
12.14
10.91

show this much plainer. We see that the separation of the lines,
in both the high protein and low protein plots, seems to have
reached its limit.

HIGH PROT. PLOT

LOW PRQT. PLOT

GENERATIONS

~f? r. r; F3 f; F, f; F, fg f^ t7„ f;,

Fig. 3. Crop averages in maize breeding for high and for low protein
Notice that the curves are each approaching a limit — the horizontal.

The important experimental data of the constancy of either of
these races has not been determined. That is, it is not known
what these strains of maize with compositions made different
from the average of unselected Burr s white through selection of
extremes, would show in their composition after several years
cessation of selection. But there is no reason to believe that

METHODS OF PLANT IMPROVEMENT. 5 1

these races are more stable than other improved races on record,
that have been established in the same way.

These two cases of sugar beets and maize are typical of all
improved races, whose improvement is due to the selection of
fluctuations. General selections to improve the yield and quality
of our farm crops, such as oats, rye, potatoes and so on, all come
under this head. Much good has been accomplished by Von
Lochow and Rimpau in Germany in increasing the yield of rye
by the use of this method of selection, but the process has been
slow and must still be continued from year to year to keep the
strain up to the excellence that has been obtained.

In this country many of the varieties of maize are due to this
selection. It is a common thing to hear of these varieties that
have been raised to a state of comparative perfection by skillful
breeders, "running out" or deteriorating in the hands of others.
This "running out of varieties" is largely a regression to their
original types by varieties that have been improved through their
fluctuations. The grower does not keep up the selection, or the
variety is ill-adapted to the soil and climate, and deterioration
is almost inevitable. On the other hand there are varieties, as
the Longfellow, whose excellence is due to desirable characters
that have been found in nature, and have been isolated, and per-
petuated. The greater constancy of these varieties is undoubtedly
due to mutating characters. Numerous constant hybrid varieties
have also been established, by combining the desirable characters
in two or more of these varieties.

There are other cases in which extreme fluctuations can be
propagated with less likelihood of their deterioration. This is by
means of bud propagation. Seedlings of many fruits and of
garden plants can be reproduced by grafts or by cuttings, so that
their variation is to a great degree lessened. There is variation
even among grafted apples and peaches, but in general this varia-
tion is too small to affect the qualities of "the fruits to a great
extent. What is the amount of this kind of fluctuation as com-
pared to that of fluctuation in varieties reproducing by seed, when
environments are comparable, is not known. We do know, how-
ever, that there is considerable variation in potatoes which are
propagated by buds (the tubers). In potatoes, however, each
plant has a more or less different environment, and much greater
differences are to be expected than with different branches on the

5 2 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

same tree. We know that potatoes must be selected within the
variety to keep them from deteriorating, but whether improvement
can be made by the selection of their fluctuations is yet unde-
termined.

Isolation of Elementary Species.

The improvement of our valuable field crops by the isolation
of the best of their elementary species has only recently attracted
attention. For the increasing prominence of this method, Nilsson
and De Vries are largely responsible.

De Vries believes Le Couteur, an English breeder on the coast
of Jersey, to have been the first to recognize that the cereals as
usually grown were full of different types. In a field of his
wheat twenty-three distinct types were found. These 'when
grown separately were true "to type and remained so generation
after generation. Some types were found that were better than
the average of the mixtures grown in the fields, and some types
were less productive and of inferior quality. A few of the better
types were isolated and multiplied as soon as possible, and put
on the market. Le Couteur's Bellevue de Talavera wheat is said
to be still grown in England and France, and is reported to be a
very uniform type.

De Vries also notes that the work of Patrick Shirreff, the
Scotch wheat grower, whose cereal breeding has been famous
for tliree-quarters of a century, was the isolation of natural types
which struck his eye. In his little book entitled "Shirreff on
Cereals" published in 1873, he says :

"My experiences in the improvements of the cereals arose
from the following cirpumstance. When walking over a field of
wheat on the farm of Mungoswell, in the county of Haddington,
in the spring of 1819, a green spreading plant attracted my notice,
the crop then looking miserable from the effects of a severe
winter, and the next day measures were taken to invigorate its
growth by removing the surrounding vegetation and applying
manure to its roots. In the course of summer several stalks
were cut down by hares; but notwithstanding this loss to the
plant, sixty-three ears were gathered from it at the harvest, yield-
ing 2,473 grains, which were dibbled in the following autumn at
wide intervals. For the two succeeding seasons the accumulating
produce was sown broadcast, and the fourth harvest of the

METHODS OF PLANT IMPROVEMENT. 53

original plant amounted to about forty-two quarters of grain fit
for seed; and proving to be a new variety it was named Mun-
goswells wheat."

Shirreff's method of improvement was the same as Le Cou-
teur's, and they both possessed the trul idea of selecting out ele-
mentary species. He says : "New varieties of the cereals can
usually be obtained from three sources — from crossing, from
natural sports, and from foreign countries." He seems to have had
no idea of the use of fluctuations in improving crops. He thought
that "sports" or wide variations of note should be separated and
multiplied. These he says, "usually breed true," and when those
which did breed true were found to be of value he immediately
set about raising seed to supply the demand. During the first
forty years he found only four plants that attracted his notice,
and from them he raised four varieties. After this time he took
up more systematic work in breeding and made several valuable
crosses among wheats and among oats.

More recently the work which has attracted wide attention
throught its intrinsic merit is that of Dr. Hjalmar Nilsson and his
associates at the Swedish Agricultural Experiment" Station at
Svalof. Here plant breeding by the Darwinian idea of the selec-
tion of fluctuations was tried, but was soon discarded because it
did not give results. In some cases improvement was made, but
even in these instances the amelioration was slow, and was
inconstant when obtained. Besides, failures were so numerous
through trying to force improvements in characters in which
nature furnished insufficient variation, that a surer method was
desired. •

A closer study of elementary species or types among the mix-
tures of plants of the cereals, grasses and clovers- as originally
grown, showed Dr. Nilsson that different types were not rare but
very numerous, so numerous in fact, that the present generation
would find them entirely adequate for their needs if they could
only give them the minute study necessary to find out their
differences and inherent qualities. Such studies have been and
still are being carried out at the Svalof station and by their means
several new varieties of oats, wheat, rye and other plants have been
isolated and introduced to cultivation. In this country the method
is being used at several Agricultural Experiment Stations. The
Cornell Agricultural Experiment Station is separating the elemen-

54 CONNECTICUT EXPERIMENT STATION BULLETIN 158.

tary types of timothy; the Minnesota Station has done a large
amount of work upon wheat and flax; while at the Connecticut
Agricultural Experiment Station the types contained in our
common clovers and ryes are being studied.

As an example of what* is to be found in the seed ordinarily
bought for pure seed of our clovers and grasses, take the medium
red clover. The seeds vary in color from white to purple. Some
of this variation is due to differences in maturity of the seeds,
but only a small portion may be so explained. There are types
with different colored stems. In some the leaves have different
patterns of white markings ; while others have plain leaves with
no markings. In some the leaves are very hairy, while others
are nearly smooth. Types are found with leaves almost smooth
at the edges ; others are contrasted with rather deep indentations.
Some run to foHage, some are profuse in blossoms, and some
produce little besides stems. The flowers are of different sizes
and colors, and the head shapes are varied. Nearly every varia-
tion needed for commercial uses can be found already produced
by nature. The general task before the breeder in a case of this
kind is plain. Individual heads from plants of all these types
must be grown in separate pedigree cultures. Then the types
which are suited to the production of the best quality of clover
hay are retained.

At Svalof it has been found that the various types of the dif-
ferent grains, legumes and grasses are adapted to different uses.
Some are resistant to certain fungous diseases, others are able to
withstand severe frosts; some are suited to clayey soils and
some ,to loose soils. In fact, the various needs of the different
parts of Sweden are fast being suited with particular types of
especially adapted plants. This is what the breeders here must
strive to do. Connecticut has various types of soil and a great
range of climatic conditions and types should be found to suit
these conditions.

The questions arise: Are these different types within a sup-
posedly pure species of cereal, grass or legume, old types per-
sistent through a long term of years, are they still arising or are
they mostly hybrid forms? The experiences at Svalof indicate
that yes must be answered to all these questions. There are
undoubtedly some very old types that have remained unnoticed
and therefore unisolated, but, nevertheless, there is absolute

METHODS OF PLANT IMPROVEMENT. 55

evidence that new types are being continually produced in a great
number of species. Many of the types are probably natural
hybrids, but this does not render them useless. They are found
in ever increasing numbers to split up in succeeding generations
according to Mendelian laws, and the delay occasioned in making
isolations is counterbalanced by the greater number of types from
which to select the needed ones.

We will summarize the distinctions between the selection of
fluctuations and the isolation of elementary species in the improve-
ment of farm crops. In each case we have a field of plants
which are supposedly of a pure and uniform variety. In reality
the field is full of elementary species — types which are slightly but
distinctly different from each other. Some of these types are
valuable, some are worthless. Taken all together they make up
the average yield and average quality that the whole field shows.
Each of these types when completely isolated from the mixture
produces a uniform progeny, with of course the usual fluctuations.
But in the field natural crossing obscures many of these types,
making the mixture still more heterogeneous.

Suppose we wish to increase the yield of these plants by the
Darwinian method of selecting fluctuations. We select out a
dozen or more of the best heads, — say of rye. We plant these
next year and again select out the best dozen heads. What have
we done? We have in all probability selected a mixture of
several types which intercross in our breeding plot. These dif-
ferent types have "blood" of types less productive in them. This
tends toward keeping up the heterogeneity of types. — good, bad
and indifferent. By continuous and very rigid selection we will
necessarily reduce the number of types in our selected rye from
the number in the original rye with which we started, but we are
never certain of reaching our aim, particularly as the process is
slow. One important reason for this uncertainty lies in the fact
that the soil of a field is never uniform. There are spots which
retain moisture a little better, and places that are a little morq
fertile than others. In these places plants belonging to poorer
yielding types will do well and are likely to be selected in place of
really better types that have grown on slightly poorer ground.

On the other hand, in the method of isolation of types by pedi-
gree cultures, these objections are in large measure overcome.
All of the types that are in the slightest degree different in their

56 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

botanical characters are grown separately. Some intercrossing
between the different types will take place, but it is much rarer
than is usually supposed. The types of most of our agricultural
plants will remain fairly pure when a reasonable distance inter-
venes between the plots. (Maize is an exception, however, and
will be' treated separately.) Some of these types are distinct
natural types and others are due to crossing. The natural types
will remain distinct and true in subsequent generations, that is,
their botanical characters will remain true. Mutations may take
place and should immediately be separated and Reproduced in
pedigree cultures by themselves. The hybrid types will split up into
different types and these should always be isolated. We will then
have a large number of types whose characters remain distinct but
in which the ordinary fluctuating variation will take place due to
slight differences in environment. These types will then need to
be studied, and the economic qualities of each noted. If a rye is
wanted that will grow upon a light soil and produce a large
amount of green forage for soiling, then a number of the types
should be tested upon that kind of soil and the best selected. If a
clover is wanted that is resistant to frost and will not winter-kill,
such a type may be found among the large number being tested.
In no case are we trying to force a variation along unnatural
lines ; we take types as nature has produced them, isolate, propa-
gate and use them. In most crops there is no need for selection
other than to obtain the necessary purity of type. The variety can
then be propagated away from danger of intercrossing and put to
commercial use as soon as sufficient seed is obtained. Those crops
which possess characters whose high fluctuations it is desirable to
perpetuate, can then be subjected to the method of continuous
selection.

Judging Plants by their Progeny. — There are two important
methods used to obtain results both in this kind of breeding and
in the selection of fluctuations. The first is judging the^value of
a type by the average value of its progeny, and the second, judg-
ing economic qualities by correlations with botanical characters.

Judging the value of a plant by its progeny was introduced*
independently by Hopkins of the Illinois Agricultural Experiment
Station, Hays of the Minnesota Agricultural Experiment Station
and Von Lochow of Germany. The principle has since come to
be generally used in breeding work. We can grow fifty to one

*This principle waS really discovered by Vilmorin and was used first by
him on sugar beets.

METHODS OF PLANT IMPROVEMENT. 57

hundred seeds from a timothy plant, a wheat plant or an ear of
maize and get a much better idea of the qualities of their mother
plants than if we grew but one or two seeds from each plant.
The seeds must of course be grown in plots by themselves so that
they can be known to be the progeny of a single plant. The
difficulties of non-uniformity of environmental conditions are thus
obviated. It is the average in the long run that counts.

Correlated Characters. — We have all noticed that dark seeds
among beans and other crops are associated with dark colored
flowers or dark colored stems or both. In some cases berries also
show dark colors associated with dark colored flowers. It is clear
in these cases that a certain amount of a coloring matter stored up
in a seed gives it a dark color which may be increased and trans-
mitted to other portions of the plant which it produces. Such asso-
ciations of character are called correlations. Many of them have
been known for years and their causes are obvious. Varieties of
sugar beets whose leaves are in open rosette form contain the
highest amount of sugar. This is what should be expected, for
with leaves growing in this form the maximum amount of sunlight
is possible for the plant, and increased amounts of sunlight make
possible increased amounts of sugar. Hopkins of Illinois has
shown that in Dent varieties of maize, kernels containing rela-
tively large amounts of the translucent homy starch of the
endosperm are comparatively higher in protein. This correlation
is explicable from the fact that this part of the kernel contains a
much higher per cent, of protein than does the white starch
portion. In very few cases, however, are the causes as obvious
as in those just given.

De Vries states that in France the common stock is culti-
vated in double-flowered and single-flowered varieties. As the
doubles produce no seed, seed to produce them is saved from the
single-flowered specimens of the same variety, since such a variety
usually produces half singles and half doubles. Owing to their
higher market price it is advantageous to separate the doubles
from the singles as soon as possible. This is done by children
who are able to pick out the doubles without error when the plants
are very small and still without branches or flower buds.
De Vries says that these differences in the seedling plants are so
small that no botanist has been able to describe them but the slight
differences which do occur are sufficient for the experienced eyes

58 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

of the children. The same writer remarks that hyacinth growers
are able to distinguish their varieties in the bulb, by the
differences in size, in the number of side bulbs, in form or in
color. Such slight markings would mean nothing to the average
gardener, but the correlations of these bulbs with the characteris-
tics of their flowers were so familiar to the Dutch hyacinth
grower, Voorhelm, that he is said to have been able to distinguish
a thousand different varieties of hyacinths solely by examining
their bulbs.

Although these correlations are evidently of different kinds and
probably of different value to the breeder, but very little work has
been done concerning their classification and probable causes.
Still the breeder should not delay putting them to use until their
precise scientific classification is known, for all classes are
undoubtedly of some practical value. In biennial and perennial
plants where large numbers of seedlings are grown and possibly a
number of years must elapse before the economic value of the
fruits can be determined, any correlations which will indicate
those plants which are absolutely worthless are of immense value
to the breeder. These plants can be rejected before a great deal
of time has been spent in their care, leaving the ground which they
would have occupied free for other plants. Likewise many com-
mercial qualities are difficult to judge, such as the milling qualities
of grains, value of plant fibres, etc. If botanical characters can
be found which are correlated with these qualities, the problem of
the improvement of such plants is greatly simplified.

The idea of the use of correlations has assumed a much
greater importance since we are but just now learning the supreme
value of the original choice in plant breeding, where the method
of breeding is the isolation of elementary species. As these ele-
mentary species when separated and found of value are to be
immediately multiplied and placed on the market, a mistake in the
original selection leaves no room for correction; for a continued
selection of fluctuations by which it is expected to breed into a
variety qualities which it does not naturally possess, is of no value.
The elementary species must first be isolated and then their agri-
cultural qualities tested ; and in these tests nothing can be of
greater value than the knowledge that a certain agricultural
quality is correlated with a definite botanical character. The
breeder can then inspect his mixture of elementary species — the

METHODS OF PLANT IMPROVEMENT. 59

commercial variety — and immediately separate the proper elemen-
tary type which carries with it the agricultural qualities which he
is seeking. At this point, after having obtained an elementary
species which naturally possesses a desirable quality as a distinct
heritable unit character, there are undoubtedly many cases in
which it is commercially profitable to use selection to keep this
character up to the highest limit in fluctuation. Note that this is
entirely distinct from trying to breed into a variety by selection a
heritable character that it does not naturally possess.

It is probable that many of these correlations will be found
to hold good only in very narrow "blood lines" of plants, and each
breeder of a particular variety of our important agricultural plants
should make it his duty to keep a systematic record of all the
correlated characters which he finds. Such a study will not only
be productive of value to the individual breeder in his own special
field, but by the general tabulation of such breeders' records, the
knowledge of correlations might finally be brought to such per-
fection that results in agricultural breeding could be obtained in
half the time it requires at present.

The value of correlations has been generally acknowledged in
this country and in isolated cases they have been put to use, still
they have not been given the amount of study to which their
importance entitles them, and we must look to Sweden as the
leader in the practical utilization. Nilsson, at the Svalof station
less than a decade ago, recognized that the study of correlations
would be of the highest values in the breeding of agricultural
crops; and he and his assistants have taken up this work. Each
species of agricultural plant is carefully described, noting all the
differences that distinguish its elementary species and at the same
time all its economic qualities. In this way all possible correla-
tions are recorded and a careful study of these tables has given
them a large number of ideas which they have put to practical use.

As an illustration of the results Nilsson has obtained by the
scientific study of correlated characters, I will give a description
of his production of the "Primus" barley as reported by
De Vries. The barley that is cultivated in the central parts of
Sweden, although of good yielding qualities, has a great
tendency to "lodge," through the weakness of its stalks. Nilsson
selected the best yielding variety, the Chevalier barley, for a
number of years to try to obtain stronger stems, but his selection

6o CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

of these fluctuating variations brought no results. Other varieties
were known with strong sturdy haulms but these were worthless as
to their brewing qualities. A careful study of the botanical char-
acters of the barley heads showed that there was a relation between
the form of hairiness to their spikelets and scales and the com-
position of the grain which makes a fine brewer's barley. Long
straight scales were correlated with coarse kernels but short crisp
wooly scales indicated the barley desired for the brewery. When
the fields of the large coarse Imperial barley with the stout haulms
were examined, out of many thousands plants about sixty were
found with the proper kind of short wooly scales. When these
were isolated and grown the next season, certain of them proved
to be an elementary species having the strong haulms of the
Imperial barley and the fine brewing qualities of the best Chevalier
varieties. The new variety was constant and uniform from the
beginning and was multiplied and placed upon the market as soon
as possible, where it now supplants the older varieties.

Improvement by Hybridisation.

This brings us to the consideration of methods of hybridization
as a means of animal and plant amelioration. The modern use of
the word hybrid is much broader in its meaning than when used by
the writers immediately succeeding Darwin. We shall apply the
term to all individuals arising from crosses between elementary
species, makirjg no distinction as to whether the parents of these
individuals belong to different Linnean genera, species or varieties.

The practical application of artificial cross- fertilization to the
production of new forms dates from the beginning of the eight-
eenth century when Thos. Fairchild, an English gardener, crossed
the carnation with the sweet william. The hybrid was almost
sterile, but proving to be a valuable variety, it was propagated
by cuttings for many years. This novelty seemingly aroused little
enthusiasm for the scientific study of crosses, and no important
generalizations were made until about 1760. At this time
Kolreuter began a systematic study of hybrids, and obtained a
knowledge of their behavior that was not greatly increased until
the last quarter of the nineteenth century.

Kolreuter established upon a firm basis Camerarius' previous
discovery of the sexuality of plants. He also found that hybrid
plants resembled the pollen (male) parent as closely as they did

METHODS OF PLANT IMPROVEMENT. 6 1

the seed (female) parent. Further, that in most cases it made
very httle difference in the final results of a cross, as to which of
the two parents was used as the pollen and which as the seed
parent. That is, the products of reciprocal crosses are nearly
identical and the male parent transmits as many characteristics to
the hybrid as the female parent.

Kolreuter, without the apparatus of the modern microscopist,
came very near discovering the mechanism of fertilization. We
now know that the application of pollen grains to the stigma of
the flower's pistils is merely a mechanical act. The pollen grain
contains a minute structure "called the nucleus, which passes down
the style of the pistil through the growing pollen tube, into the
ovary, where it unites with a similar nucleus in the ovule (fer-
tilization). F'rom this one cell the embryo in the seed and later
the whole plant is formed by exact and equal divisions. Kolreuter,
believed that fertilization consisted in the mingling together of
two vital fluids, one contained in the pollen and one contained in
the stigma, and that th,ese passing down the style started the ovule
to developing into the seed. He actually determined that about
fifty pollen grains were sufficient to mature at least thirty seeds.
It is marvelous how near the right path he was, with such limited
facilities.

Kolreuter also found that by repeatedly recrossing a hybrid with
one of the parent varieties from which it was derived, he could
finally obtain individuals that were indistinguishable from that
parent species. Furthermore, he found that there were excep-
tional cases where reciprocal crosses could not be made. Mira-
hilis jalapa (female parent) was easily crossed with Mirabilis
longiflora (male parent), but with eight years' work he did not
succeed in making the reverse cross. We now know that a
reciprocal cross is sometimes impossible, because of a seeming
mechanical inability of the nucleus of the pollen to break through
and gain admission to the nucleus of the ovule. When this
difficulty is artificially overcome the fertilization is possible.

In the beginning of the nineteenth century we have the work
of Thomas Andrew Knight, an English plant physiologist, who
has very justly been called the father of modern plant breeding.
Knight was probably the first who really appreciated the immense
possibilities of hybridization as a means of improving domestic
plants, although it is only fair to state that the principle of selec-

62 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

tion was known and made use of in improving strains of cultivated
plants by Joseph Cooper of New Jersey at a somewhat earlier
date. Kolreuter's work was theoretical, while Knight, in addition
to his contributions to theory, made definite practical use of his
knowledge gained by experiments. The commercial varieties that
he obtained through crossing were numerous and important.

Knight's greatest contributions to knowledge will probably
always be known from the two following principles that he pro-
claimed ; but science owes him a still greater debt from the fact
that he was a pioneer of the type of inductive experiment. He
generalized from his experiments instead of making theories to
prove by philosophical discussion. Knight's first principle was
that modification of the food supply is the leading cause of varia-
tion. If we write fluctuating variation instead of variation, the
principle is still accepted. He also found that the products of
crosses were often more vigorous than the parents of the hybrid ;
and that a strain of plants that had deteriorated through con-
tinued self-fertilization could be renewed in.vigor by crossing with
another strain. This conclusion has since become known as the
Knight-Darwin law. Darwin supplemented Knight's work by
many experiments comparing cross- fertilization with self-fer-
tilization and expressed his results in this terse saying: "Nature
abhors perpetual self-fertilization." Darwin's results, however,
rest on a rather slender basis. He^used characters such as heights
of plants as a measure of vigor, and these are far from desirable
standards. There are also many cases known, such as tobacco and
wheat, where self-fertilization is indefinitely continued by nature
without evil results ; in fact, with them a decrease in vigor seems
to be the immediate effect of a cross. The Knight-Darwin law
should probably be changed to read : Nature resists any sudden
change in long established conditions.

During the remainder of the nineteenth century several noted
investigators into the phenomena attending hybridization lived
and worked. Gaertner, Naudin, Focke, Vilmorin and many others
contributed large numbers of important facts, but made no great
generalization.

It was found that in general the closer the botanical relations
of two plants, the more easily they will cross. Crosses between
varieties are generally very easy to make ; those between Linnean
species have been made in quite a number of instances, while

METHODS OF CLANT IMPROVEMENT. 63

crosses between genera and families are rare, although they have
been recorded. Close botanical relationships, however, are not
unf,ailing proofs of the easy production of hybrids ; Bailey states
that the squash absolutely refuses to cross with its near relative
the pumpkin, while on the other hand Focke mentions successful
crosses between plants of the lily and amaryllisj and of the figwort
and gloxinia families. It was likewise discovered that hybrids
arising from widely different parents are usually much more
likely to be sterile than are those from nearly related parents.
But this rule is by no means without exceptions, for a number of
hybrids between different Linnean species are known that are
perfectly fertile. Sterility of hybrids among themselves does not
always unfit them as prospective commercial varieties, as they are
often fertile with one or other of their parents, and the progeny
of this cross are fertile among themselves. In other cases infer-
tile hybrids can become of great value through propagation by
means of cuttings, grafts, tubers, etc.

It was also early discovered that when two kinds of pollen were
placed on the stigma of a plant at the same time, only one kind was
effective in the fertilization. This was called prepotency of pollen.
It is thought to be due to the greater activity of some kinds of
pollen grains, since some send out their pollen tubes faster than
others and hence their nuclei reach the ovule first. The pollen of
a different variety is often prepotent over pollen from the plant
itself. In other cases, as in the potato, the plant's own pollen is
prepotent over that of other varieties.

We can see from the above short account that although many
experiments of merit were conducted, and quantities of isolated
facts were observed and recorded, still no great principle was
established until the work of Mendel which was described in
the previous chapter.

Later Mendelian Work. — We discussed the work of Mendel
practically as he left it. It seems desirable at this point, after
having outlined the work that can and has been done concerning
fluctuations and mutations, and the early work in hybridization, to
give a few short examples of the former puzzles that have been
cleared away by extensions of Mendelian principles. Bateson and
his co-workers in England, Tschermak in Austria, and Davenport,
Castle and others in the United States, are fast building up a firm
foundation for the laws of heredity from the impulse of Mendel's

64 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

work. Experimental biology has had a door of knowledge
opened comparable to that which Dalton opened for chemistry
with his atomic theory. The work will undoubtedly be slower
due to its inherent complexity, but who shall say it will not be
accomplished ?

Previously we have given explanations of Mendelian phe-
nomena stripped of the technical terms that have grown up with
the increase of Mendelian experiments. But in order to prepare
the reader who may wish to learn the latest extensions of the
theory as they are published from time to time, we will explain
such terms as are in constant use.

The cells whose nuclei unite in the process of fertilization are
called gametes or germ-cells. When these cells fuse in the pro-
cess of fertilization, a zygote is formed, and this name has been
extended to include the adult organism that is finally formed by
the succeeding divisions of this cell. Two characters with con-
trasting features which give Mendelian ratios upon inter-breeding
the product of a cross are called allelomorphs, and the pair are an
allelomorphic pair. When gametes bearing similar allelomorphs
unite to form a zygote, the product is a homozygote. For
example, the union of two yellow colored peas forms a homozy-
gote in regard to the color character. When contrasting charac-
ters of an allelomorphic pair are united in a zygote, it is called a
het era zygote: that is, the crossing of a yellow and a green pea
forms a heterozygote for color.

We remember that in cross breeding Mendel believed that
contrasting characters were united in the heterozygote, but that
when this zygote produced gametes the two factors were segre-
gated, fifty per cent, of the gametes bearing the character from
one grandparent and fifty per cent, from the other grandparent.
For example, a pea with yellow cotyledons (Y) crossed with a pea
with green cotyledons (G) produces a heterozygote whose germ-
cells bear the characters Y and G in equal proportions. Mendel's
view was that these unit characters were actual pairs of contrast-
ing characters, of which a germ-cell could possess but one.
Recently there has been some doubt as to whether this is the cor-
rect hypothesis. It has been found that in some cases,- the
extracted dominants or extracted recessives, which are the names
given to the characters which separate out apparently pure from
the cross and breed true, — have not entirely lost their possession

METHODS OF PLANT IMPROVEMENT. 65

of the contrasted character but that under certain conditions of
crossing, the other character may reappear. It seems that the
opposed character may be contained by the germ-cells, although
hidden, and may appear again when conditions are right. What
these conditions are is not known, but the phenomenon is quite
rare, and no fear need be felt that it will vitiate numerical results
in practice. Morgan has proposed the hypothesis that both char-
acters are contained in each germ-cell but only one of them shows
under ordinary conditions ; that is, one character or the other by
chance obtains the mastery in the germ-cell and shows in the
organism to the exclusion of the other character. It is illustrated
as follows:

A(B) (A)B

A(B) (A)B

iA(B)+2A(B) (A)B+i(A)B.

Representing by A the dominant character and by B the reces-
sive character, if at some time after making the cross the A
character becomes the master of half the germ-cells of both male
and female, it may be represented as A(B). In the other half
of the germ-cells the B character obtains the mastery and the
cell may be represented as (A)B. Separations then take place
after crossing as is shown in the formula. In the first and third
term, the free characters (the one outside the parenthesis) show,
while in the second or hybrid term, the A character shows because
it is thought to be dominant when both A and B are "free"
characters.

Morgan's proposition is that the characters are not separated
in the gametes but that the contrasting characters are both pres-
ent but one always in a latent condition which can sometimes
be made patent by proper crossing. This view explains some of
these exceptional cases but a larger number of others are inexpli-
cable by it. The view which has so far explained by far the
largest number of cases is called the presence and absence hypoth-
esis and was propounded by Bateson.

On this hypothesis a yellow pea is based on green; i. e., the
yellow color is superimposed upon the green. The yellow pea
produces gametes bearing two factors, one for yellowness (Y)
and one for greenness (G). When it is self- fertilized or fertil-
ized with another yellow pea a zygote is produced whose gametes

66 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

have the formula YG but the resulting zygotes always have the
yellow color through the presence of the yellow factor.

In the same way the pure green pea produces gametes carrying
two factors — one for greenness (G) and one for absence of
yellowness (y).

In cross breeding the yellow pea producing gametes YG
would meet the green pea producing gametes yG and the result-
ing zygote will be a yellow hybrid whose constitution is YGyG.
The hybrid zygote would produce gametes YG and yG in equal
quantities, which meeting by chance upon self-fertilization would
give the following results :

YG > YG

pollen YG ^^ YG egg

cells yG ^"^ yG cells

yG > yG

The results would be numerically and, apparently, the same as
those of the Mendelian hypothesis. Those zygotes whose formu-
lae are YGYG would be pure yellow superimposed upon green,
those whose formulae are YGyG would be hybrid yellow super-
imposed upon green, and those whose formulae are yGyG, by the
absence of yellow (y), would be green.

We do not know what is the precise nature of the absence
factor in the germ-cell. Three hypotheses have been presented:
there may be (i) an actual substance representing absence, (2)
there may be literally nothing, or (3) there may be presence
but in a latent state. The third view is much the same as
Morgan's, but it is open to the objection that cases are known in
which the "presence" factor is itself latent — cases which-
Morgan's theory would explain.

Whatever is the explanation, it may very well be that these
pairs of unit characters represented by two allelomorphs are
really two pairs of characters. Let us recall that two pairs of
characters were shown by Mendel to give four classes of zygotes
in the F^* generation in the proportions 9 13 13 :i. Now if the two

* Hybridizers use the letter Fi (= ist filial generation) to represent the
immediate product of a cross. The succeeding generations arising from
the Fi generation are denoted by the letters F2, F3, etc. The parents of
the Fi generation are called Pi (='ist parental generation), and the grand-
parents Pa, and so on.

METHODS OF PLANT IMPROVEMENT. 67

first classes were indistinguishable for some reason and the two
last also alike, we would have the proportion of 12 to 4, or 3 to i.
Hurst has shown this to be actually the case in a large number
of experiments on both plants and animals, and has been able to
distinguish between 'the different classes.

On crossing the Fireball tomato (possessing a red flesh show-
ing through a yellow skin) with the Golden Queen (possessing
yellow flesh showing through a white skin), he obtained an F^
generation which was exactly like the Fireball, red being domi-
nant to yellow. Upon self-fertilizing the F^ generation there was
a segregation in the F^ generation into reds and yellows, with
the expected Mendelian ratio of three reds to one yellow. How-
ever, there were found to be four distinct types, two reds, and
two yellows. These four types occurred in ratio of 9:3:3:1 as
follows : nine with red flesh through a yellow skin ; three with a
red flesh through a white skin ; three with yellow flesh through a
yellow skin; one with yellow flesh through a white skin. Mr.
Hurst thinks that it is quite probable that the two pairs of
factors under consideration are (i) presence (R) and absence
(r) of red in the flesh, and (2) the presence (Y) and the absence
(y) of yellow in the skin ; presence being the dominant character
in each case. The red is superimposed upon the yellow and when
the factor for the presence of red is there the zygote is red ;
but when the factor for the absence of red is there the zygote is
yellow. The point is that while the red and yellow types of
tomatoes behave as Mendelian characters with the red dominant,
there are really four types which can be isolated and will breed
true. The conception of the presence and absence factor may
be a little puzzling at first but not more puzzling than the
chemists' physical conception of the atom. It is as if dominance
were the outcome of the presence of a certain factor, and reces-
siveness the result of its absence. If we strip off dominance,
we have recessiveness.

Masked Characters. — This construction of a presence and
absence hypothesis has been the means of clearing up several
important cases which at first appeared unconformable to the
Mendelian ratio. Hurst found upon crossing a pure bred "Bel-
gian Hare" rabbit with a grey coat, with a 'pure bred "White
Angora" with a white coat that all of the offspring of the F^
generation were grey. But oddly enough in the F^ generation

68 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

there appeared an approximate ratio of nine grey, three black,
four white.

This ratio appears to be due to two sets of characters : a color
factor C dominant to absence of color c, and greyness G dominant
to blackness b. The gametes of the Belgian Hare would have
the formulae (C + G), and those of the albino the formula
(c-|-b). The albino actually carries the factor for black (b)
but the black color is invisible because of the absence of the
color factor (C). When both C and G are present, the animal
is grey; when both C and b are present the animal is black.
But both G and b may be present without the color factor C and
the animal will still be white. Moreover, out of the four albinos
produced, three carry the color factor (b) while one is without
it. The four albinos are alike in appearance and if bred together
will give only albinos. But if they are bred to blacks carrying
the color factor, it is found that three of the albinos carry either
a pure grey G or a hybrid grey (Gb) factor, while the other
carries only a pure black factor. Thus we really have two
classes among the albinos with the ratio of 3:1, and instead of
the 9 :3 14 ratio that appears to have been obtained, we actually
have the true Mendelian expectancy for two pairs of characters,
9 :3 :3 :i. These cases, where two classes of individuals appear as
one class, are called cases of masked characters.

The accompanying diagram will help elucidate the case. If
we represent color by C (dominant) and no color by c (recessive)
then by crossing the two characters we get an individual with a
gametic formula CCcc in the F^ generation and with self-fer-
tilization the ratio CC + ^Cc + cc in the F^ generation. We will
represent these four individuals by the four large squares in the
diagram. If in the other pair of characters greyness G is
dominant to blackness b, by crossing and then self-fertilizing
the offspring, we get the ratio GG -|- 2Gb -f- bb in the F2 genera-
tion. This we represent by subdividing the four large squares,
for there is an equal chance that each of the four classes repre-
sented by the large squares will fertilize one individual of each
of the classes represented by the four small squares. Notice
that there are nine squares criss-crossed where C and G both
are present ; these represent individuals with both color and grey-
ness present and these individuals appear grey. In the three solid
squares color C and no grey, or blackness b, are present and the

METHODS OF PLANT IMPROVEMENT.

69

individuals that they represent are black; in the four white
squares the color factor C is absent and the individuals that they
represent are all albino. However, in thre.e of the albino squares
G is present, either pure as GG or hybrid as Gb ; these individuals
carry the grey color masked and it can be brought out by proper
crossing. The other albino carries the black color b which is
recessive in grey, also masked, and this too can be brought out by
proper crossing. s,

Reversion. — Another very important phenomenon that has
long puzzled hybridists has been found to yield to a simple
Mendelian explanation. I refer to the phenomenon of reversion.

1 1

1 1

—

1

1

1

LLG_

(;w

[^(tI

Ub

1

4c

c cc-

r

j!c

Cc-

K.

1 ' 1

r>

cc^Hi

C' 1

cJH

"

(;■)

(;hi

jjm

^^■■■^1

'

;■

I

1 1

'

: GG

cc

Gb
cc

(t(4

Gh

_r>

c- Cc

1 p

c Cc^H cc
ilB^^H Gb

cc

bb

(;b

1 1

_J||H

■

■

1.

1

Fig. 4. Masked characters

or appearance of an ancestral character on crossing. It has long
been known that by crossing two pure individuals that each breed
true to a particular color ; individuals would sometimes be found
in the F^ generation that show the color of a bygone ancestor.
The phenomenon is known in both animals and plants but is illus-
trated nicely by the sweet pea.

There are^itwo white varieties of the sweet pea, each of which
breeds true to white, but Bateson found that upon crossing, the F^
generation are all purple. Then upon self-fertilizing or inter-
breeding the Fi generation, nine purples and seven whites appear
out of every sixteen plants of the Fg generation. It is clear that

70 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

each race of whites contains one factor necessary for the produc-
tion of the old ancestral purple of the sweet pea, but as neither
variety contains both factors, each breeds true to white until
they are brought together. The two factors are color (C) domi-
nant to absence of color (c) and purple (P) dominant to absence
of purple (p) ; but since one variety has gametes with the formula
color plus absence of purple (C -|- p), it is white, and since the
other variety has the gametic formula purple plus absence of
color (P -f" c), it is also white. If we make use of the same style
of diagram in this case, using *CC + 2Cc + cc to represent the
color factor in the large squares, and PP -f- 2Pp -f- pp to repre-
sent the purple factor in the four small squares of each large
square, the matter is entirely clear. Wherever P and C are

"Hi 1

- cn : : CE : ; c: ' uk ~

"On ~D"0 ~Q "D

rr rP - Pp Pp

-- VPVP — P.Pp

- cr cc : cs cc

1

cc r.c cc Cc

Pp Pp -j- t^p pp

-- Pp Pp PP PP

^c cc Cc CO

Fig. 5. Reversion

present in the same square the individual is purple, but where
either P or C is absent (represented by p or c) the individual
is white. There are nine squares in which the P character
brought by one variety is in combination with the C character
brought by the other variet)' and these represent nine purple
individuals. Likewise, there are seven squares in "Which either
the P character or the C character, or both, are absent; they
therefore represent white individuals. It is simply a case where
the ratio of 9:3:3:1 has the last three terms combined and the
ratio is 9:7.

METHODS OF PLANT IMPROVEMENT. 7 1

Heterozygotes. — We have already stated that dominance in a
complete form is not universal in cases of Mendelian inheritance.
In fact in possibly the majority of cases the dominant character
appears in a diluted form in the hybrid progeny of a cross.
There are other cases jvhere the segregation of the characters
takes place according to Mendelian ratios but the appearance of
the hybrid is totally different from either of the parent types.
This class of hybrids has in the past been a stumbling block to
breeders, because they have tried to "fix" this character which
they now know is from its very nature an impossibility.

This is the case with the blue Andalusian fowl. No matter
how carefully this type is selected and inter-bred, poultry breeders
have never been able to get it absolutely true. About half come
true to the blue character,- while of the remainder one-half are
black and the other half white with black splashes. The very
fact that these proportions were the Mendelian expectation from
a cross — i part black: 2 parts blue: i part splashed white — led
Bateson to believe that the blue character was merely the charac-
teristic appearance of the heterozygote due to the crossing of the
black and the splashed white. This was found by crossing to be
the correct view. Curious and paradoxical as it may seem, by
inter -breeding the "pure" blues only one-half of the offspring
came blue, but by breeding together the blacks and the splashed
whites all of the offspring were blue. These, however, split
into the three classes, as would be expected, in the next genera-
tion. "The riddle of the impossibility of obtaining a pure race
of blue Andalusians was thus solved." The very nature of the
case showed that the breeders were following a will-o'-the-wisp.

There have already been several valuable practical applications
of these laws in problems of breeding. Mr. R. H. Biffen, in
England, has found that susceptibility and immunity to rust in
wheat are a pair of simple Mendelian characters in which
immunity is the recessive. He has by this knowledge been able
to produce in only three generations a pure race of rust-resistant
wheat. Spillman has shown that the polled character in cattle
dominates the horned character, and that by proper crossing a
polled race of cattle can be established, with only a single polled
mutation as foundation stock. Thus when single characters are
of supreme importance, our knowledge of a plan of action is of

72 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

greatest value. We know that we must avoid trying to obtain in
combination both of a pair of contrasted characters. We know
that we must breed for one character at a time, for by referring
to the table on page 43 we can see that with six pairs of characters
we must have 4,096 individuals to obtain one with all six dominant
characters combined.

It has been stated that Mendel's work will make the characters
of hybrids as easy to predict as are those of chemical compounds.
This is taking an extreme view of the case. The production of
hybrids is work of great complexity owing to the great number
of unit characters that make up the higher plants and animals.
What we are coming to know is the most direct plan of procedure
in combining known desirable characters possessed by distinct
varieties. Before predictions concerning the results of hybridiz-
ing can be made, it must be known for all of our domestic plants
and animals what characters Mendelize and which of each pair
is dominant. There is an enormous amount of work yet to be
done, before we will be able to refer to a book giving lists of
important characters of different plants which will Mendelize
together with the characters which they dominate or by which
they are dominated. Mendel has originated a new style of
experimental work, — the careful observance of individual charap-
ters in each of the offspring of a 'cross. He has brought con-
firmatory evidence that characters are established fully formed
by mutation, and are inherited as such.

In conclusion it may be stated that the general idea has been
that it is only hybrids between varieties that follow Mendelian
laws, but there are already several records of characters in both
elementary* species and Linnean species that obey them, and
many more cases will undoubtedly be brought into conformity
when a larger number of types have been studied.

* De Vries distinguishes between elementary species and varieties, in
that the elementary species of a Linnean species are of equal rank and
usually differ from each other in several characters, while varieties, he
says, are derived from elementary species and differ from them in ways
which are common in a large number of species. Varieties, he thinks, are
less striking in their differences and follow different laws of inherita.nce
when crossed. This appears to the writer to be an arbitrary distinction,
and the correctness of his conclusions will remain in doubt until more
light is thrown on the question.

technique in plant breeding. 73

Technique in Plant Breeding.

In the subject matter up to this point, special methods for the
improvement of particular crops have been purposely omitted.
As the work in plant breeding increases in size and scope, methods
more or less suited to each important field crop will doubtless be
published. Experiments are necessary to determine the proper
details for such work. Many mistakes are to be expected, due
largely to the complicated data from which conclusions must be
drawn. It is hoped that a study of the underlying principles of
variation and heredity will reduce the fallacious proceedings of
breeders to a minimum and give them ability to criticize the
weak points in the methods which have been proposed for their
use. The most important contributions to the technique of breed-
ing will probably be made by those who, like the Vilmorins in
France, are well abreast with the science of the day, and yet who
regard the work from its commercial side. The balance sheet
of any business is a great teacher of quick and direct methods.

Although this paper aims only to give a short introduction to
the principles of breeding and consequently must necessarily omit
the discussion of the improvement of individual crops, still a few
examples of technique in breeding will be given in order to make
clearer the explanation of the theoretical part. Following a
statement of the essential points with which the hybridizer must
be familiar, are given (i) the important features of breeding to
isolate elementary species, using red clover, trifolium praetense L.
as a type, and (2) criticisms of the modern method of breeding
our most important crop, maize. The latter is an example of a
crop where both elementary species and fluctuations are dealt
with in practice.

Flowers and their Parts.

A flower is said to be complete when it has calyx, corolla,
stamens and pistils. Of these the calyx and corolla are called
the floral envelopes. The calyx is the outer whorl of leaf -like
parts of the flower, and is usually green. The showy part of
the flower is usually the corolla. The different shapes of the
floral envelopes in nature show wonderful adaptation to make

74 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

certain fertilization and hence to assure the production of seed.
In artificial pollination we have to do only with the stamens and
pistils which are called the essential organs of the flower. The
important feature of the stamen is the pollen grains. These are
borne within the enlarged terminal part of the stamen called the
anther. When the pollen grains mature the anthers open and the
pollen can then be seen as a yellowish or brownish dust. Each of
these minute pollen grains contains at least one nucleus or essen-
tial part of a reproductive cell." The pollen grains are the male
reproductive cells of the plant. The pistil, whether simple or
compound, has three parts when complete. The stigma at the
upper end is generally rough or flattened or sticky in order to hold
the pollen when it is applied. This actual application of pollen
to the stigma, whether by insects or wind or by the hand of man,
is pollination. When pollen grains are applied to the stigma, the
sticky substance upon the latter causes them to grow. This
growth is called the pollen tube. It makes a pathway down
through the style — ^the slender part of the pistil — and finally
reaches the female or egg-cell in the interior of an ovule in the
lower part of the pistil called the ovary. The male nucleus passes
down this pollen tube and unites with the female nucleus in the
ovule; this process is fertilisation.

Fertilization in plants may bring about a much closer degree
of relationship than it may in animals ; fertilization may be
effected by pollen which was produced upon the same flowers or
the same plant upon which the ovules grew. This is self -fer-
tilisation. Fertilization by the union of pollen and ovules which
grew upon dififerent plants of the same "pure line," that is, sister
or cousin plants, gives different degrees of close-fertilisation.
Union between plants of different "pure lines," whether of the
same or different varieties, is cross-fertilisation.

Cross-fertilization appears to be important to a large number
of plants, for there are many devices in nature by which cross-
fertilization is effected. Natural cross- fertilization is effected
by water, wind and insects, although the first agency is so rare
among cultivated plants that it can be disregarded. Wind-
pollinated plants are called anemophilous (wind loving), while
those pollinated b)^ insects are said to be entomophilous (insect
loving).

TECHNIQUE IN PLANT BREEDING. 75

Flowers that contain both stamens and pistils are known as
perfect or hermaphrodite flowers. A very common means of
insuring cross-fertilization among these plants is to have the
stamens and the pistils mature at different times. When the
stamens mature first, as in the hollyhock, the flower is pro-
tandrous; when the pistils mature first the flower is proter-
ogynous. Flowers of either of these kinds are known as
dichogamous. When flowers lack either pistils or stamens they
are said to be incomplete or diclinous, and are called staminate
or pistillate according to which organs are present. When the
staminate and pistillate flowers are borne on the same plant, as
with chestnuts, walnuts, squashes, maize and others, the plant is
monoecious. When the different kinds are borne upon separate
plants, as willow and hemp, the plant is dioecious.

The entomophilous flowers are generally distinguished by
irregular corollas which are so adapted that insects visiting
them for nectar are almost certain to pollinate them with pollen
they have brushed from other flowers. The artificial pollination
of this class of flowers is difficult because of the care that must
be taken to prevent injury to the essential organs while removing
the floral envelopes preliminary to applying the pollen. There is
also a class of flowers which pollinate themselves before opening,
thus insuring self-fertilization. They are called cleisto gamous
flowers. Examples of this class are rare, and usually the same
plant bears flowers of some other class. A careful examination
of the common blue violet will show a few inconspicuous cleis-
togamous flowers down beneath the showy blue ones.

Technique of Hybridizing.

Success from artificial crossing only comes from close study
of the. difficulties attending the work, in each particular case.
There are four points with which the operator must be familiar.

I. The natural habits of the plant in its fertilization. It must
be known whether the plant is diclinous or complete ; and whether
the stamens and pistils mature at the same or at different times.
These facts will be given in any manual of botany. The
hybridizer must find out by experience, however, whether early,
medium or late flowers are the best seed producers, and whether
care must be taken to pollinate sufficiently at the first application.

76 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

or whether several applications can be made to the same flower,
before the pistil falls.

2. The maturity of the pollen. The pollen is generally ready
for use when nature releases it from the anthers. But in dif-
ferent plants flowers of different times of opening produce pollen
in different amounts and of different degrees of viability. In
some cases the flowers that open first produce but little pollen and
this unhealthy. It may be that in other cases the late blossoms
should not be used. Healthy pollen has a regular shape, char-
acteristic of the species or variety to which it belongs, but when
examined under the microscope it should always be plump.
Shriveled, irregular pollen of pure forms should be discarded.
It should be recognized, however, that it is characteristic of many
hybrids that the ability to form perfect pollen is lessened.

3. The maturity of the stigma. The proper time for the
application of the pollen to thp stigma varies from the time of
the opening of the flower in some species until three or four days
later in others. An examination of the stigma with a hand lens is
of some value; for in some types the stigmas are quite profuse
with a gummy exudation at the time the stigma is most receptive.
In many types, however, experience alone will show when to
make the cross. An absolute record upon this point is very
important for every specialist who breeds a particular crop, for
Hartley has shown that premature pollination is quite injurious
in cases of tobacco, orange, cotton and tomato that he had
investigated.

4. Prevention of pollination other than that which is intended.
Not only must the entrance of foreign pollen be provided against,'
but in all perfect blossoms, precautions must be taken that self-
fertilization is prevented. To prevent self-fertilization the
flowers must be emasculated — that is, the anthers must be
removed — before the blossom opens. When the blossoms are
comparatively large this is easily done by cutting off both the
corolla and stamens with a small pair of surgeon's scissors.
If it is in the way the calyx also may be removed. In case the
flowers to be used are small, a pair of very fine tweezers with the
points slightly flattened may be used. When using tweezers the
anthers should be removed with considerable care, as they may be
opened mechanically, allowing the flower to self-pollinate.
When operating upon composites or upon flowers borne in large

TECHNIQUE IN PLANT BREEDING. 77

numbers upon heads or spikes, most of the flowers and flower
buds should be removed, leaving only three or four individual
buds somewhat isolated from each other. Each of these should
then be emasculated.

In monoecious or dicecious plants, it is of course only necessary
to protect against foreign pollen, as is likewise done with complete
flowers after their preparation by removing the anthers. Ordi-
nary paper bags such as are used by the grocer serve very well
for protection. They should be moistened at the end so they can
be tied close to the stem of the emasculated bud. In particularly
careful work, we should also bag the pollen parent, but in com-
mercial hybridizing sufficient pollen can usually be obtained by
shaking the flowers over a watch glass. There is in this case a
possibility of contamination, but the relative probability of it is
small. When the stigma is receptive, it should be dipped in the
pollen if it is available in sufficient amount; otherwise it can be
applied with a small camel's hair brush. After pollination the
flower should immediately be rebagged, and labelled with the
date and the name of the pollen parent. After several days, when
fertilization has taken place, it is better to change the paper bag
to a cheese cloth bag, which will serve the purpose of retaining
the fruit should it be dropped, and at the same time admit light
and air.

In certain cases the stigmas of the plant to be used as the seed
parent are not ready for some time after pollen has been obtained.
When this happens the pollen should be slowly and carefully
dried under glass, then put away in a tightly corked glass vial.
If the pollen is dried too fast, rapid evaporation of moisture
causes the grains to split, and the pollen is rendered useless ; but
when dried with care some kinds of pollen — grapes, for instance —
will retain their vitality for a whole year.

Technique of Isolating Elementary Species.

In breeding field crops by the isolation of elementary species
there are three things to be accomplished: i. The separation of
the elementary species ; 2. Comparison of the different types ;
3. Rapid propagation of selected types for commercial use. As
a typical example of this kind of breeding we will use the
experience of others and ourselves in the breeding of our com-
mon red clover, trifolium praetense L.

78 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

The first point to be observed in separating- the natural types
of any species, is to find out the probabiHty of natural crossing.
In maize, where large amounts of pollen are formed and pollina-
tion is entirely anemophilous, natural crossing is so great that
isolation of pedigree cultures is almost impossible. In the case
of smaller plants which commonly cross in nature, a framework
covered with very fine cheese cloth is placed over individual
plants from which foreign pollen is to be kept. Sometimes a few
humble bees are placed in the tent to make pollination more
certain. This method is often used with choice plants of the red
clover, although it has been recently found that self-pollination
is much more common than Darwin supposed. The crop of
seed from a field in which humble bees (their chief insect pol-
linating agent) are common, is much larger than the crop in fields
with few of these visitors, but nevertheless the amount of self-
pollination is very considerable, and the separation of individual
plants by a few feet of space renders their isolation comparatively
easy even without cloth screens.

The breeder begins by selecting seed from individual plants
growing in a mixed field. He also selects seeds of different
sizes, shapes and colors from the commercial product. These
seeds are planted in hills about two and one-half feet each way.
The seeds of each individual plant are planted in separate plots,
making the product of each plot the progeny of a single plant of
the year before. Each of these plots and each plant in the plot
bears a separate number, which is the means of reference to the
description that is always carefully kept of all plants that are to
be again propagated. It is only by these minute descriptions of
characters that the different types can be separated, for it is
impossible for a breeder to keep in mind the exact distinctions
between types. When a plant is found in a plot that is different
from the others, its flowers are separately bagged and pollinated.
If it appears worthy of further consideration its seed is planted
in another plot the next year.

The seed from each plot is not mixed for planting the next
year's plot. If there are different types in a single plot, they
have their seed saved separately and each plant of a slightly
different type has a different plot for planting its seed in the
succeeding fall. In no case does seed from more than one plant

TECHNIQUE IN PLANT BREEDING. 79

enter a plot. The breeding is distinctly in-and-in breeding-, for
this is the only way in which we can expect to separate the types.-
Of course many of these plants are rejected each year as
useless types, otherwise the work would become too un\Adeldly to
conduct with proper economy of time and space. The remainder
are gradually separated into distinct types which reproduce their
characteristics year after year, and are then selected or rejected as
their commercial value or uselessness becomes apparent. Varia-
tions that we have noted, that are of agricultural value, include
the following:

(a) In vigor: some succumb to frost and their usefulness
comes to a natural end ; others are resistant and come through the
winter in the best of shape ;

(b) In stooling: some produce a large number of stalks;
others very few ;

(c) In leafiness : some produce long, weak stems, with leaves
only at wide intervals, while others are remarkable for their
leafiness ;

(d) In character of bloom: some have numerous heads,
others few ; some beads are large, others small ; some bear large
individual flowers, others small ;

(e) In habit of growth: some are erect and are easily cut by
the mower, while others are recumbent ;

(f) In yield: the differences are very marked;

(g) In character of stem: some are hard and woody, others
make better hay.

There are many other differences that serve to help distinguish
the types, but these differences are in slight physical distinctions
that are probably of no agricultural value. It is true that these
botanical marks may be found to be correlated with valuable
qualities when they can be more closely studied with this idea in
view.

Out of all the different types probably but two or three will be
found of particular merit. The others must be discarded and
the selected strains multiplied for field use, as rapidly as possible.
The superior strains are not mixed but each are propagated
separately as different varieties.

It is hoped before many years we will have varieties of each
of the different forage grasses and legumes, as we now have
garden varieties, adapted for special purposes. The important

8o CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

way to obtain valuable improvement of such crops is by isolation
of naturally better strains from their present mixtures. Hybridi-
zation may be necessary later, but at present it is undesirable to
complicate the work until we have accomplished what can be done
without it.

Technique of Maize Breeding.

The breeding of maize or Indian corn is in many ways quite
different from the breeding of our other field crops. Maize is
the only one of our cereals that is monoecious. The tassel con-
tains the pollen or male element while the silks are the stigmas of
female flowers. In order that the pollination of the silks shall
be relatively certain, each tassel produces about thirty million
pollen grains; and as the ears average considerably less than
five hundred grains apiece, there are about sixty thousand pollen
grains produced for each kernel. With such a large waste of
pollen floating about in the air, there are a great number of inter-
crosses between plants of the same variety. This inter-crossing
has been an obstacle to the improvement of maize, but it has been
offset by the advantage over the other cereals, in the possession
of large ears* Since each individual ear must be handled and its
characters noted at husking time, it is not strange that ears with
desirable variations sufficiently striking to catch the eye of the
grower, have become the parents of numerous distinct varieties.

It was early learned that maize varieties inter-crossed freely
and the lesson was heeded by the pioneers in maize breeding. By
selecting seed ears toward a desired type and by isolation from
other varieties, various strains have been produced that are
remarkably uniform in characters such as color, that have
forcibly attracted the attention of the grower. Nevertheless,
even in an isolated maize field grown from seed that comes pretty
true to type, such as the Longfellow flint or the Reid's yellow dent,
there are many natural types grov/ing side by side. There are
stalks which bear their ears high and there are stalks which bear
them low ; stalks with long ear shanks and stalks with short,
stalks with different leaf markings and with notably different
tendencies to produce suckers. The silks shade in color from
purple to green as do also the tassels. Differences are every-
where present, although those in the ears themselves are the most
familiar.

TECHNIQUE IN PLANT BREEDING. 8l

A large number of these differences are due solely to fluctua-
tions, which are more easily noted in the large stalks and ears of
maize than they are in the smaller plants of cereals like wheat
and rye. The variations due to fluctuations are so large that the
natural types are more or less obscured. Furthermore, the
natural types are in a very mixed condition due to constant cross-
ing with other types by wind pollination. We have on this account
a much harder task than in most plants to separate the naturally
productive types. Moreover, after a complete separation of such
types there is still the wide and valuable fluctuating variation to
consider ; for to obtain the best results from breeding with such a
large fruited plant as maize, the highest fluctuations in yield must
be constantly selected and perpetuated.

To sum the matter up there are these tasks before the breeder :

1. To isolate the best yielding and otherwise desirable natural
types of maize from the varieties in which the "blood" of these
types is in a chaotic mixture with the "blood" of less desirable
types ; and to do this in the face of constant chances of further
inter-crossing.

2. Constantly to select and propagate the highest fluctua-
ting variations of desirable characters.

To solve these two problems has been the sole aim of maize
breeders; and has been the means of building up the various
methods of maize breeding now in use in the United States.
Each of these methods has its advantages and its disadvantages,
which the writer will try to discuss without bias, hoping that the
advantages of each may sometime be combined into a more
perfect method than there is at present. At least it is the right
of the commercial breeder to know just what obstacles are in the
way of the highest success; he may then adjust a method to
meet his own conditions, without being led away by false hopes
of large profit from blindly following the introducer of an
imperfect method. We leave out of consideration, because of
previous discussion, the fact that there may be definite strong
points in two varieties which it may be desirable to combine by
hybridization. This of course should be done when it is desirable,
but there are probably natural types now being grown that answer
all present agricultural purposes could we but get from them
their greatest possibilities. Even to secure best results from
hybridizing we must start with pure types.

82 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

In the primitive method of selecting large ears from the crib,
the selections were especially poor in point of germination; for
the ears were not properly dried and many of them were partially
mouldy. While this is particularly bad for the yield in the suc-
ceeding season, it has very little to do with the hereditary charac-
ters of maize. The fluctuating variations in the succeeding
season would be affected by the weak diseased stalks produced
by seed embryos with poor vitality ; but there is little probability
of the weakness becoming permanent. Indeed, long continued
selection of this kind does have quite an effect toward separa-
ting a particular natural type because the grower naturally
selects those ears that appeared to be nearest in character to his
ideal.

The first improvement over this primitive method was selection
in the fieldjy The advantage of this method over the crib selection
was that the characters of the plant which bore the ear could
be taken into consideration as well as the characters of the ear
itself. Hence progress in separating natural types was much
faster than formerly. It was this method that gave us such
varieties as Leaming and Reid's yellow dent and Longfellow flint
varieties. These varieties, in the hands of conscientious breeders,
have been brought to the most uniform type of any varieties
that we possess. Furthermore, when selections were made in the
field more care was naturally taken with the selected ears, which
ultimately made germination better and hence gave larger total
yields. Field selections were made by the most progressive
growers as early as the first half of the nineteenth century.

Not much over ten years has elapsed since the next step was
taken in maize breeding. This was the introduction of what is
now called the row system of breeding made by Hopkins at the
Illinois Agricultural Experiment Station. The principle is, that
more definite idea of the productive efficiency of an individual ear
can be obtained by getting the average record of its progeny.
That is, when one hundred or more hills are planted from a single
ear and compared at the end of the season with rows of equal
lengths from other ears, the weights of the ears produced on each
row are a more exact measure of the productive efficiency of
the mother ear of that row than are the weights of one or two of its
daughter ears, selected at random. The average appearance of the
progeny of an ear is a more correct index of the productiveness of

TECHNIQUE IN PLANT BREEDING. 83

a mother ear than is the appearance of the mother ear itself, for
slight differences in soil fertility, "moisture or sunlight may
largely have been the cause of a superior looking ear, and
this superiority might not be transmitted to any great degree
to succeeding generations. In fact it often happens that in
testing two seed ears, practically alike in size and appear-
ance, by this method, that one yields at double the rate of the
other. This is a great contribution toward a quicker method
of isolating natural types, because a row that is exceedingly
uniform in type growing from a single mother ear, shows
that it (the mother ear) is less likely to carry the blood of
numerous other natural types, than is the ear from which comes
a varied progeny. Nevertheless, there is in this method the dis-
advantage that in planting these rows in the open field, there is
a very large chance of inter-crossing between a superior row
and an inferior row growing near it. Moreover, it is obviously
incorrect to measure the productive capacities of two rows grow-
ing at opposite sides of a large field on account of very probable
inequalities of soil. The disadvantage of inter-crossing in the
row system was to a slight degree overcome by the United States
Department of Agriculture, by the introduction of a plot system
similar in character to the one previously described for clover.
Kernels of single ears planted together in plots have the chances
for inter-crossing with other types minimized, at least for the
stalks growing toward the centre of each plot. But the advantage
of this system is offset by the greater difficulty of planting, har-
vesting and keeping the records of the progeny of the individual
ears, without making mistakes by which mixtures of other types
would be introduced.

It has been suggested by the Ohio Agricultural Experiment
Station that the error of comparing distant rows with each other
can be decreased by the duplication of rows from the same mother
ear in different parts of the field ; while at the Illinois Agricultural
Experiment Station it has been proposed to reach the same end
by comparing with each other only ears which grew in one-quarter
of the breeding plot. Selections were made of the best rows in
each quarter of the breeding plot. Later the Ohio Experiment
Station introduced the plan of planting so-called standard rows
between every five rows. These standard rows were made b^
■planting in each one a certain number of kernels from the

84 CONNECTICUT EXPERIMENT STATION BULLETIN I58.

same ears. The rows between two of these standard rows were
not compared with each othfer but with the average product of the
two standard rows between which they grew. It is evident that
it is not desirable to perpetuate these standard rows made up of
composite samples of several ears. To keep from doing this, in
the method of continuous selection, it is necessary to detassel all
of these standard rows, thus preventing any possibility of pollen
which they had produced fertilizing silks of other rows.

About this same time an extended experiment at the Illinois
Station showed that there were distinct effects from continuous
propagation from very .nearly related blood lines such as is
ordinarily obtained in a rigidly selected breeding plot. To
decrease this fault it was suggested to detassel every alternate
row and to select seed for the succeeding season only from the
detasseled rows. A plan* of planting was worked out mathe-
matically by which near relatives were separated. A breeding
plot of ninety-six rows was grown, and every alternate row
detasseled, leaving in all forty-eight rows from which seed might
be selected. These forty-eight rows were considered in four
quarters and four ears were selected from each of the six best
producing rows of each quarter. Of these twenty-four ears
selected in each quarter, twelve were grown the next season in
that quarter and detasseled ; the other twelve were taken to the
farthest removed quarter and grown the next season in rows that
were not detasseled. In this way the blood lines were continu-
ously kept as far apart as is possible in an open field breeding plot.

It is clear that while this method lessens the evil effect of
inbreeding and is easy to manipulate, it nevertheless does very
little toward isolating natural types because of the selection each
year of so many ears for the next year's breeding plot. On the
other hand, the propagation of the highest extremes of fluctua-
tions was brought to a high degree of perfection.

This method, however, does contribute toward the slow isola-
tion of the best natural. high yielding type, for the selection is
made each year from high yielding rows, that is, from the prog-
eny of the best mothers, which gradually weeds out the least pro-
ductive types. The pollen parents are of course unknown although

**This plan is explained in detail in Bulletin No. 152 of this station,
which will be mailed free upon request.

TECHNIQUE IN PLANT BREEDING. 85

they must be better than the general field average because they
come each year from the best yielding rows of the previous sea-
son; but there is no way always to guard against the pollination
of the best detasseled rows by relatively inferior tasseled rows.
The influence of very inferior individuals or rows, however, is
guarded against by detasseling all weak and barren stalks as well
as the regular detasseled rows. Rows that produce a large number
of undesirable stalks are entirely detasseled to prevent the inferior
blood of the parent ear from being propagated. Another point
in which this method is inefficient is that a small number of
rows are used in the beginning. If there could be an initial selec-
tion of a very large number of ears, there would be a much greater
probability of a final isolation of the best types now being
naturally produced. The number of ears planted in succeeding
years could be materially decreased, for the relative probability
of obtaining bipod of the best natural types in the first selection
is much greater than where small numbers are used; and
having partially isolated these types by the first selection,
it would not be so necessary or even desirable to continue
using large numbers. But even if this were done, there
remains an obstacle in the fact that even with a large number
of ears selected from the general field for the first breeding plot,
there would still be an indefinite number of crosses among these
selections ; that is, it cannot be known what per cent, of inferior
blood there was in the original ears which were selected as appear-
ing to be the best. It may be that from this cause a relatively
pure ear of a comparatively ordinary type would show up to
better advantage in a breeding plot than an ear of a superior type
but with a large admixture of an inferior type. Moreover, when
the selection is made af the end of the first season from the best
yielding rows, there is nothing to guard against these selected
ears having been pollinated from inferior rows in proximity,
and at this stage the rows are all from field selections with no
previous breeding. Hand pollination is of little practical use, for
we could not tell definitely until harvest which rows would prove
the best and a large amount of tedious work would have to be
done which would ultimately prove useless.

Williams, of the Ohio Agricultural Experiment Station,
obviates this deficiency by the method he has originated. He
plants twenty-five rows in an ear-to-the-row test plot but uses only

86

CONNECTICUT EXPERIMENT STATION BULLETIN I58.

one-half of the kernels of each ear. This test plot is treated as
an ordinary field plot with no necessity of detasseling or remov-
ing suckers. The rows, however, are weighed at the end of the
season and compared with a standard row which is made up as
described above (page 83) and planted between every five rows.
The remnants of the four ears that have been shown to possess
the greatest yielding efficiency are planted the succeeding season
in two small isolated plots, detasseling all the plants grown from
one ear in each plot. By saving the seed only from the
detasseled rows, a direct cross is obtained of two of the best
ears upon the other two selected ears. In the third season ears
from each of these crosses are again crossed by planting in
alternate rows and detasseling the even numbered rows. Each
year new field selections are grown in test plots and the remnants
of the two ears which prove the best are crossed the following
season. Finally, these are again crossed with best ears from
previous crosses. This is continued indefinitely, as is shown in
the following diagram.

I ST YEAR

20 YEAR

4TH YEAR 5TH YEAR

6THYEAR

CROP

Fig. 6. Williams' method of maize breeding. (After Shamsl.)

This method has' two advantages : it does away with any pos-
sibility of the selected ears having been crossed during their
ear-to-the-row test with pollen of inferior types and yet does not
allow the strain to deteriorate through inbreeding. * Its dis-
advantages are :

TECHNIQUE IN PLANT BREEDING. 87

1. There is only a small number of ears in the first breeding
plot which makes the chance of isolation of the best types rela-
tively small. This is supposedly obviated by taking the ears for
the test rows each year from the general field; but the objec-
tion to this proceeding is that new mixtures of elementary types
are thereby introduced into the improved strain. High fluctua-
tions are thus continually brought into the strain, but the isola-
tion of the best type is further than ever frorn attainment.

2. It is necessary to grow three isolated plots each year, which
on many seedsmen's farms is almost an impossibility.

3. There is not sufficient range for the selection of fluctuating
variations in such small plots, after the individual ear crosses
are made.

It appears, therefore, that there are advantages and disad-
vantages belonging to each method, without there having been
suggested a particularly desirable combination of the two. Where
there is sufficient uniform soil available, and where the breeder
is going to devote his whole time to the development of maize,
the following method is proposed as worthy of consideration,
although it also leaves much to be desired. In the first year let
the breeder obtain select ears of the variety from different
growers, of as many different desirable types as possible. Let
these ears be selected from standing plants where possible, pay-
ing strict attention to the character of the plants that bear the
selected ears. The stalks should be firm and erect, with a good
secondary root system and plenty of foliage. The ears should be
borne between three feet six inches and five feet high, on medium
length ear shanks, and should be covered with only a moderate
amount of husk. They should be mature, and should contain the
largest possible weight of kernels of uniform size and shape,
where the time of maturity is not an object. In places where the
growing season is short, smaller ears should be selected, but
from plants that produce more than one ear, for we have found
that a pound of corn can be produced by a plant bearing two
ears, in a shorter time than a pound of corn can be produced upon
a single ear. Other fancy score card points need be given little
attention, as what we wish to obtain is a variety that produces the
greatest profit per acre. This we shall find out by actual test
without carrying into it a preconceived .notion of just which type
is the most productive.

88 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

At least three hundred of these ears should be planted in the
first year's ear-to-the-row test, and five hundred or more should
be grown if possible. These ears should each be numbered and
only one-half of the kernels of each planted in single rows in the
test plot. Our object is to have the greatest possible probability
of obtaining the best natural types from the first year's test.
Notes should be taken of the desirable or undesirable qualities
shown by the plants of each row, at various stages of growth,
and at the end of the season each row should be cut, husked and
weighed separately.

All of the corn from the best fifteen or twenty rows should be
saved separately and the ears and plant records of these rows
carefully studied. All rows whose products show a number of
undesirable characteristics should be entirely discarded. Some
rows will have shown a marked superiority over all others. The
ears from those rows should be examined minutely to see whether
they bear any peculiarities that may be correlated with productive
efficiency. If any such peculiarities are found, note them in the
record book, for the value of the knowledge of such a correlation
to the breeder can hardly be estimated.

The next season plant the remnants of the four ears that had
this season produced the four rows with the most marked
superiority over the rest. These ears will possess the supe-
riority shown in the test, uncrossed by inferior pollen in the test
plot to the previous season. They will probably not be distinct
and uniform types, for it is likely that they contain blood of other
types from previous natural crosses in the field ; but they are the
pick of a large number of ears, and partially or wholly true to
type as the case may be; they are good foundation stock for a
uniform variety.

There are now two methods of procedure open:

1. To begin at once to select high fluctuations, without trying
to isolate further a single type.

2. To risk evil effect from inbreeding and work to isolate
further a more uniform foundation stock.

In the first method the plan of planting can be arranged by
planting in alternate rows with as many combinations as pos-
sible. Then by detasseling the upper half of each odd numbered
row and the lower half of each even numbered row, force as many
different crosses as possible on these rows. Save the best ears of

TECHNIQUE IN PLANT BREEDING. 89

these crosses and begin a regular ear-to-the-row fluctuation breed-
ing* plot and continue it annually, using from fifty to one hundred
rows.

The second method can be followed most practically by planting
the remnants of the best four ears in pedigree plots. Each plot
is then surrounded by two rows of some very high growing
ensilage corn planted one kernel every eight inches. These rows
are to obstruct foreign pollen and should be carefully detasseled
each season. Personally I prefer to use immediately the fluctua-
tion plot on account of danger of continued inbreeding, but I
am free to confess that the question is not permanently settled.
There may be individuals that will stand continued inbreeding
like Darwin's morning glory. Hero.

The point of extreme importance is the advantage of isolating
immediately from the general field as fine a foundation stock as
possible. The relative probability of doing this increases directly
with the number of ears used in the first test plot; hence as large
a number as possible should be used. If we obtain a fine founda-
tion stock we are on the road to success ; if we have left the best
stock out of our first test plot, no amount of continued breeding
from the inferior stock can obtain it.

Conclusion.

These pages are designed only to give the practical plant
breeder an introduction to the theoretical side of his subject.
There are hundreds of agriculturists who are interested in the
work of improving their important field crops, and yet who know
nothing of the work of their colleagues in the science either pure
or applied. In many cases the methods in use are primitive as
those of several centuries past. In other instances much impracti-
cal advice is followed blindly. We now have plant breeder's
associations in a large number of our states, as well as a national
organizationf with over a thousand members, where information
can be obtained upon special subjects. It is hoped that readers
of this paper that expect to do plant breeding work, will become
members of some of these associations and take up a course of

* A breeding plo,t in which high fluctuations in yield are selected.

t The American Breeders' Association. For information address, Hon.
W. M. Hays, Secretary, Washington, D. C. The Connecticut Plant
Breeders' Association, Prof. C. D. Jarvis, Secretary, Storrs, Conn.

go CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

reading along the lines suggested in the appended list. The
reading will be found fascinating as well as instructive and the
association with men interested in similar lines of work will prove
to be of great value.

The writer is well aware that he can be accused of a pronounced
De Vriesian view of this paper. He can only plead that the
view is from the standpoint of the principles and theories that
give at present the most practical and efficient help in actual plant
breeding. As was stated in the beginning, the studies of the
evolution student and of the plant breeder should be and are
parallel, but only in so far as theories are proposed that can be
experimentally demonstrated. Experimental proof on all points
is the ideal of the modern biologist, but it is absolutely essential
to the modern breeder. The philosophical side of biology can
have but little weight with the latter. It may be admitted that
certain forces may have been of great value in effecting an evolu-
tion through eons of time, and still be ineffective agents in the
time allotted to the man who wishes to make changes under
domestication from the standpoint of commercial gain. It is
here that the two lines part company ; and it is the plant breeder
who remembers this distinction between natural and artificial
evolution when studying disputed theories of variation and
heredity, that will obtain the greatest aid from the results of the
experimental biologist. We may admit, for instance, that the
believer in Lamarckian factors as agents in evolution can say
that experiments concerning the inheritance of acquired charac-
ters have been carried on only for a period of time that would be
negligible in a geological epoch ; we may admit the justness of
the same criticism of our conclusions regarding the ineffective-
ness of the selection of fluctuations in permanently changing
characters : but we are justified in retorting that only such
theories can be of use to us that produce results within the span
of a human life. With this point in mind the writer believes that
a fair view has been taken of the questions touched upon in this
paper.

Our three main theses we will again summarize :

I. Organisms are composed of numbers of characters which

are inherited as units. These units are inherited by definite laws

of which Mendel's law is the first to have been discovered. Since

these characters are inherited as units it is most reasonable to

TECHNIQUE IN PLANT BREEDING. 9 1

suppose that each one haS been originated fully formed, i. e., as
a mutation. The addition of a new unit character is the only real
difference between this mutating organism and its progenitors,
and is the true and only foundation for domestic improvement.

2. The object of hybridization is to shuffle and recombine these
unit characters. Hybridization, therefore, actually produces
nothing new in spite of its wonderful manifestations. Just as
chemical units, — the elements, — can be combined and recombined
into different compounds, so can the unit characters of organisms
be combined and recombined by hybridization.

3. The value of the selection of fluctuations is slightly to
increase or to decrease the manifestations of a unit character
after it has been formed by nature. Selection can never produce
a unit character, for there is obviously no basis upon which it
could work.

92 CONNECTICUT EXPERIMENT STATION BULLETIN 1 58.

, Reading List.

This list of publications is suggested as a course of supple-
mentary reading in English, concerning the questions that have
been under discussion, and is available to most readers through
the public libraries. The reading should be done cautiously, for
it must be remembered that most of these publications were issued
previous to the rediscovery of Mendel's work, in 1900. If the
works of De Vries, Mendel and later workers of the Mendelian
school are studied first, the reader will appreciate how great has
been the change of opinion during the last seven years concern-
ing these questions, and will not be confused by the different
points of view of the early writers. The recent work is scattered
through the files of many journals, and is for the most part in
foreign languages. For these reasons it is not available to many
readers and has therefore been omitted from the list. To remedy
this omission, it is recommended that the reader obtain from his
bookseller, as soon as they are published, the two forthcoming
volumes on the problems of variation and heredity by Wm. Bate-
son, M.A., F.R.S., Fellow of St. John's College, Cambridge.

Bailey, L. H. Plant Breeding. Ed. 4. N. Y. Macmillan. 1906,

Contains a fairly complete bibliography to the end of 1905.
Bailey, L. H. Evolution of oui- Native Fruits. N. Y. Macmillan. 1898.
Gives a popular historical account of the development of American
varieties of fruits.
Darwin, Chas. Cross and Self-fertilization in the Vegetable Kingdom.
N. Y. D. Appleton.

Read chapters one and twelve, giving the plans of the experiments and
results.
Darwin, Chas. Animals and Plants under Domestication. 2 v. Ed. 2.
N. Y. D. Appleton.

The historical parts of the first volunie are still of great interest.
The theoretical discussions in volume two will only be confusing to
the reader and had best be omitted. Our views concerning the explana-
tion of the phenomena brought together in volume one have entirely
changed since Darwin's time.
De Vries, Hugo. Species and Varieties: Their Origin by Mutation.
2d Ed. Chicago. Open Court. 1906.

A large book which goes rather deeply into the subject. It has in it
more of interest to plant breeders than any other book concerned with
evolution.

READING LIST. 93

DeVries, Hugo. Plant Breeding. Chicago. Open Court. 1907.

A work that is of special interest to plant breeders. It should be
read before the larger work. Gives an account of Nilsson's work in
Sweden and Burbank's work in the United States.
Kellogg, V. L. Darwinism To-day. N. Y. Henry Holt. 1907.

Gives the best summary of modern criticism of Darwin. The author
does not accept the mutation theory.
Lock, R. H. Variation, Heredity and Evolution. London. John
Murray. 1906..

The best popular presentation of the subject from the modern view-
point. Contains the summation of important researches up to 1906.
Morgan, T. H. Evolution and Adaptation. N. Y. Macmillan. 1903.

A good criticism of Darwin by one who accepts the mutation theory.
Punnett, R. C. Mendelism. Ed. 2. Cambridge. Macmillan. 1907.

A short and readable account of Mendelism to date of publication.
Romanes, G. J. Darwinism. Ed. 3. Chicago. Open Court. 1901.

An excellent account of Darwin's theory of natural selection; the
early criticisms and Romanes' replies.

The following articles, although written without a knowledge
of Mendelism, which would change their statements to some
extent, are recommended as a set of interesting papers that may be
obtained free from any Congressman or from the Secretary of
Agriculture, Washington, D. C. Either the complete year books
will be sent or the separate articles may be obtained as reprints.

Bailey, L. H. The Improvement of our Native Fruits. Year book

U. S. D. A. 1896: pp. 297-304.
Hays, W. M. Progress in Plant and Animal Breeding. Year book U. S.

D. A. 1901: ppi 217-232.
Swingle, W. T. and Webber, H. J. Hybrids and their Utilization in

Plant Breeding. Year book U. S. D. A. 1897: pp. 383-420.
Webber, H. J. Influences of Environment in the origination of Plant

Varieties. Year book U. S. D. A. 1896: pp. 89-106.
Webber, H. J. Improvement of Plants by Selection. Year book U. S.

D. A. 1898: pp. 355-376.
Webber, H. J. and Bessey, E. A. Progress of Plant Breeding in the

United States. Year book U. S. D. A. 1899: pp. 465-490.

9 7C-Q

n o

f^ i U -J

U o

University of
Connecticut

Libraries

39153029221027