The improvement of cultivated plants must obviously begin with already
existing forms. This is true of old cultivated sorts as well as for
recent introductions. In either case the starting-point is as important
as the improvement, or rather the results depend in a far higher degree
on the adequate choice of the initial material than on the methodical
and careful treatment of the chosen varieties. This however, has not
always been appreciated as it deserves, nor is its importance at present
universally recognized. The method of selecting plants for the
improvement of the race was discovered by Louis Vilmorin about the
middle of the last century. Before his time selection was applied to
domestic animals, but Vilmorin was the first to apply this principle to
plants. As is well known, he used this method to increase the amount of
sugar in beets and thus to raise their value as forage-crops, with such
success, that his plants have since been used for the production [93] of
sugar. He must have made some choice among the numerous available sorts
of beets, or chance must have placed in his hands one of the most
appropriate forms. On this point however, no evidence is at hand.
Since the work of Vilmorin the selection-principle has increased
enormously in importance, for practical purposes as well as for the
theoretical aspect of the subject. It is now being applied on a large
scale to nearly all ornamental plants. It is the one great principle now
in universal practice as well as one of preeminent scientific value. Of
course, the main arguments of the evolution theory rest upon
morphologic, systematic, geographic and paleontologic evidence. But the
question as to how we can coordinate the relation between existing
species and their supposed ancestors is of course one of a physiologic
nature. Direct observation or experiments were not available for Darwin
and so he found himself constrained to make use of the experience of
breeders. This he did on a broad scale, and with such success that it
was precisely this side of his arguments that played the major part in
convincing his contemporaries.
The work of the breeders previous to Darwin's time had not been very
critically performed. Recent analyses of the evidence obtained [94] from
them show that numerous types of variability were usually thrown
together. What type in each case afforded the material, which the
breeder in reality made use of, has only been inquired into in the last
few decades. Among those who have opened the way for thorough and more
scientific treatment are to be mentioned Rimpau and Von Rumker of
Germany and W.M. Hays of America.
Von Rumker is to be considered as the first writer, who sharply
distinguished between two phases of methodical breeding-selection. One
side he calls the production of new forms, the other the improvement of
the breed. He dealt with both methods extensively. New forms are
considered as spontaneous variations occurring or originating without
human aid. They have only to be selected and isolated, and their progeny
at once yields a constant and pure race. This race retains its character
as long as it is protected against the admixture of other minor
varieties, either by cross-pollination, or by accidental seeds.
Improvement, on the other hand, is the work of man. New varieties of
course can only be isolated if chance offers them; the improvement is
not incumbent on chance. It does not create really anything new, but
develops characters, which were already existing. It brings [95] the
race above its average, and must guard constantly against the regression
towards this average which usually takes place.
Hays has repeatedly insisted upon the principle of the choice of the
most favorable varieties as the foundation for all experiments in
improving races. He asserts that half the battle is won by choosing the
variety which is to serve as a foundation stock, while the other half
depends upon the selection of parent-plants within the chosen variety.
Thus the choice of the variety is the first principle to be applied in
every single case; the so-called artificial selection takes only a
secondary place. Calling all minor units within the botanic species by
the common name of varieties, without regard to the distinction between
elementary species and retrograde varieties, the principle is designated
by the term of "variety-testing." This testing of varieties is now, as
is universally known, one of the most important lines of work of the
agricultural experiment stations. Every state and every region, in some
instances even the larger farms, require a separate variety of corn, or
wheat, or other crops. They must be segregated from among the hundreds
of generally cultivated forms, within each single botanic species. Once
found, the type may be ameliorated according to the local conditions
[96] and needs, and this is a question of improvement.
The fact that our cultivated plants are commonly mixtures of different
sorts, has not always been known. The first to recognize it seems to
have been the Spanish professor of botany, Mariano Lagasca, who
published a number of Spanish papers dealing with useful plants and
botanical subjects between 1810 and 1830, among them a catalogue of
plants cultivated in the Madrid Botanical Garden. Once when he was on a
visit to Colonel Le Couteur on his farm in Jersey, one of the Channel
Islands off the coast of France, in discussing the value of the fields
of wheat, he pointed out to his host, that they were not really pure and
uniform, as was thought at that time, and suggested the idea that some
of the constituents might form a larger part in the harvest than others.
In a single field he succeeded in distinguishing no less than 23
varieties, all growing together. Colonel Le Couteur took the hint, and
saved the seeds of a single plant of each supposed variety separately.
These he cultivated and multiplied till he got large lots of each and
could compare their value. From among them he then chose the variety
producing the greatest amount of the finest, whitest and most nutritious
flour. This he eventually placed in the [97] market under the name of
"Talavera de Bellevue." It is a tall, white variety, with long and
slender white heads, almost without awns, and with fine white pointed
kernels. It was introduced into commerce about 1830, and is still one of
the most generally cultivated French wheats. It was highly prized in the
magnificent collection of drawings and descriptions of wheats, published
by Vilmorin under the title "Les meilleurs bles" and is said to have
quite a number of valuable qualities, branching freely and producing an
abundance of good grain and straw. It is however, sensitive to cold
winters in some degree and thereby limited in its distribution. Hallett,
the celebrated English wheat-breeder, tried in vain to improve the
peculiar qualities of this valuable production of Le Couteur's.
Le Couteur worked during many years along this line, long before the
time when Vilmorin conceived the idea of improvement by race selections,
and he used only the simple principle of distinguishing and isolating
the members of his different fields. Later he published his results in a
work on the varieties, peculiarities and classification of wheat (1843),
which though now very rare, has been the basis and origin of the
principle of variety-testing.
The discovery of Lagasca and Le Couteur was [98] of course not
applicable to the wheat of Jersey alone. The common cultivated sorts of
wheat and other grains were mixtures then as they are even now. Improved
varieties are, or at least should be, in most cases pure and uniform,
but ordinary sorts, as a rule, are mixtures. Wheat, barley and oats are
self-fertile and do not mix in the field through cross-pollination.
Every member of the assemblage propagates itself, and is only checked by
its own greater or less adaptation to the given conditions of life.
Rimpau has dealt at large with the phenomenon as it occurs in the
northern and middle parts of Germany. Even Rivett's "Bearded wheat,"
which was introduced from England as a fine improved variety, and has
become widely distributed throughout Germany, cannot keep itself pure.
It is found mingled almost anywhere with the old local varieties, which
it was destined to supplant. Any lot of seed exhibits such impurities,
as I have had the opportunity of observing myself in sowings in the
experimental-garden. But the impurities are only mixtures, and all the
plants of Rivett's "Bearded wheat," which of course constitute the large
majority, are of pure blood. This may be confirmed when the seeds are
collected and sown separately in cultures that can be carefully guarded.
[99] In order to get a closer insight into the causes of this confused
condition of ordinary races, Rimpau made some observations on Rivett's
wheat. He found that it suffers from frost during winter more than the
local German varieties, and that from various causes, alien seeds may
accidentally, and not rarely, become mixed with it. The
threshing-machines are not always as clean as they should be and may be
the cause of an accidental mixture. The manure comes from stables, where
straw and the dust from many varieties are thrown together, and
consequently living kernels may become mixed with the dung. Such stray
grains will easily germinate in the fields, where they find more
congenial conditions than does the improved variety. If winter arrives
and kills quantities of this latter, the accidental local races will
find ample space to develop. Once started, they will be able to multiply
so rapidly, that in one or two following generations they will
constitute a very considerable portion of the whole harvest. In this way
the awnless German wheat often prevails over the introduced English
variety, if the latter is not kept pure by continuous selection.
The Swiss wheat-breeder Risler made an experiment which goes to prove
the certainty of the explanation given by Rimpau. He observed on his
farm at Saleves near the lake of Geneva that after a lapse of time the
"Galland wheat" deteriorated and assumed, as was generally believed, the
characters of the local sorts. In order to ascertain the real cause of
this apparent change, he sowed in alternate rows in a field, the
"Galland" and one of the local varieties. The "Galland" is a race with
obvious characters and was easily distinguished from the other at the
time when the heads were ripe. They are bearded when flowering, but
afterwards throw off the awns. The kernels are very large and yield an
extraordinarily good, white flour.
During the first summer all the heads of the "Galland" rows had the
deciduous awns but the following year these were only seen on half of
the plants, the remainder having smooth heads, and the third year the
"Galland" had nearly disappeared, being supplanted by the competing
local race. The cause of this rapid change was found to be twofold.
First the "Galland," as an improved variety, suffers from the winter in
a far higher degree than the native Swiss sorts, and secondly it ripens
its kernels one or two weeks later. At the time of harvest it may not
have become fully ripe, while the varieties mixed with it had reached
maturity. The wild oat, _Avena fatua_, is very common in [101] Europe
from whence it has been introduced in the United States. In summers
which are unfavorable to the development of the cultivated oats it may
be observed to multiply with an almost incredible rapidity. It does not
contribute to the harvest, and is quite useless. If no selection were
made, or if selection were discontinued, it would readily supplant the
cultivated varieties.
From these several observations and experiments it may be seen, that it
is not at all easy to keep the common varieties of cereals pure and that
even the best are subject to the encroachment of impurities. Hence it is
only natural that races of cereals, when cultivated without the utmost
care, or even when selected without an exact knowledge of their single
constituents, are always observed to be more or less in a mixed
condition. Here, as everywhere with cultivated and wild plants, the
systematic species consist of a number of minor types, which pertain to
different countries and climates, and are growing together in the same
climate and under the same external conditions. They do not mingle, nor
are their differentiating characters destroyed by intercrossing. They
each remain pure, and may be isolated whenever and wherever the
desirability for such a proceeding should arise. The purity of [102] the
races is a condition implanted in them by man, and nature always strives
against this arbitrary and one-sided improvement. Numerous slight
differences in characters and numerous external influences benefit the
minor types and bring them into competition with the better ones.
Sometimes they tend to supplant the latter wholly, but ordinarily sooner
or later a state of equilibrium is reached, in which henceforth the
different sorts may live together. Some are favored by warm and others
by cool summers, some are injured by hard winters while others thrive
then and are therefore relatively at an advantage. The mixed condition
is the rule, purity is the exception.
Different sorts of cereals are not always easily distinguishable by the
layman and therefore I will draw your attention to conditions in
meadows, where a corresponding phenomenon can be observed in a much
simpler way.
Only artificial pasture-grounds are seen to consist of a single species
of grass or clover. The natural condition in meadows is the occurrence
of clumps of grasses and some clovers, mixed up with perhaps twenty or
more species of other genera and families. The numerical proportion of
these constituents is of great interest, and has been studied at
Rothamstead in England and on a number of other farms. It is [103]
always changing. No two successive years show exactly the same
proportions. At one time one species prevails, at another time one or
two or more other species. The weather during the spring and summer
benefits some and hurts others, the winter may be too cold for some, but
again harmless for others, the rainfall may partly drown some species,
while others remain uninjured. Some weeds may be seen flowering
profusely during some years, while in other summers they are scarcely to
be found in the same meadow. The whole population is in a fluctuating
state, some thriving and others deteriorating. It is a continuous
response to the ever changing conditions of the weather. Rarely a
species is wholly annihilated, though it may apparently be so for years;
but either from seeds or from rootstocks, or even from neighboring
lands, it may sooner or later regain its foothold in the general
struggle for life.
This phenomenon is a very curious and interesting one. The struggle for
life, which plays so considerable a part in the modern theories of
evolution, may be seen directly at work. It does not alter the species
themselves, as is commonly supposed, but it is always changing their
numerical proportion. Any lasting change in the external conditions will
of course alter the average oscillation and the influence [104] of such
alterations will manifest itself in most cases simply in new numerical
proportions. Only extremes have extreme effects, and the chance for the
weaker sorts to be completely overthrown is therefore very small.
Any one, who has the opportunity of observing a waste field during a
series of years, should make notes concerning the numerical proportions
of its inhabitants. Exact figures are not at all required; approximate
estimates will ordinarily prove to be sufficient, if only the standard
remains the same during the succeeding years.
The entire mass of historic evidence goes to prove that the same
conditions have always prevailed, from the very beginning of cultivation
up to the present time. The origin of the cultivation of cereals is to
be sought in central Asia. The recent researches of Solms Laubach show
it to be highly probable that the historic origin of the wheat
cultivated in China, is the same as that of the wheat of Egypt and
Europe. Remains of cereals are found in the graves of Egyptian mummies,
in the mounds of waste material of the lake-dwellings of Central Europe,
and figures of cereals are to be seen on old Roman coins. In the
sepulchre of King Ra-n-Woser of the Fifth Dynasty of Egypt, who lived
about 2000 years B.C., two [105] tombs have recently been opened by the
German Oriental Society. In them were found quantities of the tares of
the _Triticum dicoccum_, one of the more primitive forms of wheat. In
other temples and pyramids and among the stones of the walls of Dashur
and El Kab studied by Unger, different species and varieties of cereals
were discovered in large quantities, that showed their identity with the
present prevailing cultivated races of Egypt.
The inhabitants of the lake-dwellings in Switzerland possessed some
varieties of cereals, which have entirely disappeared. They are
distinguished by Heer under special names. The small barley and the
small wheat of the lake-dwellers are among them. All in all there were
ten well distinguished varieties of cereals, the Panicum and the Setaria
or millet being of the number. Oats were evidently introduced only
toward the very last of the lake-dwelling period, and rye is of far
later introduction into western Europe. Similar results are attained by
the examination of the cereals figured by the Romans of the same period.
All these are archaeologic facts, and give but slight indications
concerning the methods of cultivation or the real condition of the
cultivated races of that time. Virgil has left us some knowledge of the
requirements of methodical [106] culture of cereals of his time. In his
poem _Georgics_ (I. 197) the following lines are found:
_Vidi lecta din, et multo spectata labore
Degenerare tamen, ni vis humana quotannis
Maxima quaeque manu legeret_.
(The chosen seed, through years and labor improved,
Was seen to run back, unless yearly
Man selected by hand the largest and fullest of ears.)
Elsewhere Virgil and also some lines of Columella and Varro go to prove
in the same way that selection was applied by the Romans to their
cereals, and that it was absolutely necessary to keep their races pure.
There is little doubt, but that it was the same principle as that which
has led, after many centuries, to the complete isolation and improvement
of the very best races of the mixed varieties. It further proves that
the mixed conditions of the cereals was known to man at that time,
although distinct ideas of specific marks and differences were of course
still wholly lacking. It is proof also that cultivated cereals from the
earliest times must have been built up of numerous elementary forms.
Moreover it is very probable, that in the lapse of centuries a goodly
number of such types must have disappeared. [107] Among the vanished
forms are the special barley and wheat of the lake-dwellings, the
remains of which have been accidentally preserved, but most of the forms
must have disappeared without leaving any trace.
This inference is supported by the researches of Solms-Laubach, who
found that in Abyssinia numerous primitive types of cereals are still in
culture. They are not adequate to compete with our present varieties,
and would no doubt also have disappeared, had they not been preserved by
such quite accidental and almost primitive isolation.
Closing this somewhat long digression into history we will now resume
our discussion concerning the origin of the method of selecting cereals
for isolation and segregate-cultivation. Some decades after Le Couteur,
this method was taken up by the celebrated breeder Patrick Sheriff of
Haddington in Scotland. His belief, which was general at that time, was
"That cultivation has not been found to change well defined kinds, and
that improvement can be best attained by selecting new and superior
varieties, which nature occasionally produces, as if inviting the
husbandman to stretch forth his hand and cultivate them."
Before going into the details of Sheriff's work it is as well to say
something concerning [108] the use of the word "selection." This word
was used by Sheriff as seen in the quotation given, and it was obviously
designed to convey the same idea as the word "lecta" in the quotation
from Virgil. It was a choice of the best plants from among known mixed
fields, but the chosen individuals were considered to be representatives
of pure and constant races, which could only be isolated, but not
ameliorated. Selection therefore, in the primitive sense of the word, is
the choice of elementary species and varieties, with no other purpose
than that of keeping them as pure as possible from the admixture of
minor sorts. The Romans attained this end only imperfectly, simply
because the laws governing the struggle for life and the competition of
numerous sorts in the fields were unsuspected by them.
Le Couteur and Sheriff succeeded in the solution of the problem, because
they had discovered the importance of isolation. The combination of a
careful choice with subsequent isolation was all they knew about it, and
it was one of the great achievements to which modern agriculture owes
its success.
The other great principle was that of Vilmorin. It was the improvement
within the race, or the "amelioration of the race" as it was termed by
him. It was introduced into [109] England by F.F. Hallett of Brighton in
Sussex, who at once called it "pedigree-culture," and produced his first
new variety under the very name of "Pedigree-wheat." This principle,
which yields improved strains, that are not constant but dependent on
the continued and careful choice of the best plants in each succeeding
generation, is now generally called "selection." But it should always be
remembered that according to the historic evolution of the idea, the
word has the double significance of the distinction and isolation of
constant races from mixtures, and that of the choice of the best
representatives of a race during all the years of its existence. Even
sugar-beets, the oldest "selected" agricultural plants, are far from
having freed themselves from the necessity of continuous improvement.
Without this they would not remain constant, but would retrograde with
great rapidity.
The double meaning of the word selection still prevailed when Darwin
published his "Origin of Species." This was in the year 1859, and at
that time Shirreff was the highest authority and the most successful
breeder of cereals. Vilmorin's method had been applied only to beets,
and Hallett had commenced his pedigree-cultures only a few years before
and his first publication of the "Pedigree-wheat" [110] appeared some
years later at the International Exhibition of London in 1862. Hence,
whenever Darwin speaks of selection, Shirreff's use of the word may as
well be meant as that of Vilmorin.
However, before going deeper into such theoretical questions, we will
first consider the facts, as given by Shirreff himself.
During the best part of his life, in fact during the largest part of the
first half of the nineteenth century, Shirreff worked according to a
very simple principle. When quite young he had noticed that sometimes
single plants having better qualities than the average were seen in the
fields. He saved the grains, or sometimes the whole heads of such plants
separately, and tried to multiply them in such manner as to avoid
intermixtures.
His first result was the "Mungoswell's wheat." In the spring of 1819 he
observed quite accidentally in a field of the farm of that name, a
single plant which attracted his attention by a deeper green and by
being more heavily headed out. Without going into further details, he at
once chose this specimen as the starting point of a new race. He
destroyed the surrounding plants so as to give it more space, applied
manure to its roots, and tended it with special care. It yielded 63
heads and nearly [111] 2500 grains. All of these were sown the
following fall, and likewise in the succeeding years the whole harvest
was sown in separate lots. After two years of rapid multiplication it
proved to be a good new variety and was brought into commerce. It has
become one of the prominent varieties of wheat in East Lothian, that
county of Scotland of which Haddington is the principal borough.
The grains of "Mungoswell's wheat" are whiter than those of the allied
"Hunter's wheat," more rounded but otherwise of the same size acid
weight. The straw is taller and stronger, and each plant produces more
culms and more heads.
Shirreff assumed, that the original plant of this variety was a sport
from the race in which he had found it, and that it was the only
instance of this sport. He gives no details about this most interesting
side of the question, omitting even to tell the name of the parent
variety. He only asserts that it was seen to be better, and afterwards
proved so by the appreciation of other breeders and its success in
trade. He observed it to be quite constant from the beginning, no
subsequent selection being needed. This important feature was simply
assumed by him to be true as a matter of course.
[112] Some years afterwards, in the summer of 1824, he observed a large
specimen of oats in one of the fields of the same farm. Being at that
time occupied in making a standard collection of oats for a closer
comparison of the varieties, he saved the seeds of that plant and sowed
them in a row in his experiment-field. It yielded the largest culms of
the whole collection and bore long and heavy kernels with a red streak
on the concave side and it excelled all other sorts by the fine
qualities of its very white meal. In the unequal length of its stalks it
has however a drawback, as the field appears thinner and more meager
than it is in reality. "Hopetown oats," as it is called, has found its
way into culture extensively in Scotland and has even been introduced
with success into England, Denmark and the United States. It has been
one of the best Scottish oats for more than half a century.
The next eight years no single plant judged worthy of selection on his
own farm attracted Shirreff's attention. But in the fall of 1832 he saw
a beautiful plant of wheat on a neighboring farm and he secured a head
of it with about 100 grains. From this he produced the "Hopetown wheat."
After careful separation from the kernels this original ear was
preserved, and was afterwards exhibited at the Stirling Agricultural
[113] Museum. The "Hopetown wheat" has proved to be a constant variety,
excelling the ordinary "Hunter's wheat" by larger grains and longer
heads; it yields likewise a straw of superior quality and has become
quite popular in large districts of England and Scotland, where it is
known by the name of "White Hunter's" from its origin and the brilliant
whiteness of its heads.
In the same way Shirreff's oats were discovered in a single plant in a
field where it was isolated in order to be brought into commerce after
multiplication. It has won the surname of "Make-him-rich." Nothing is on
record about the details of its origin.
Four valuable new varieties of wheat and oats were obtained in this way
in less than forty years. Then Shirreff changed his ideas and his method
of working. Striking specimens appeared to be too rare, and the
expectation of a profitable result too small. Therefore he began work on
a larger scale. He sought and selected during the summer of 1857 seventy
heads of wheat, each from a single plant showing some marked and
presumably favorable peculiarity. These were not gathered on one field,
but were brought together from all the fields to which he had access in
his vicinity. The grains of each of these selected heads were [114] sown
separately, and the lots compared during their whole life-period and
chiefly at harvest time. Three of the lots were judged of high
excellence, and they alone were propagated, and proving to be constant
new varieties from the outset were given to the trade under the names of
"Shirreff's bearded white," "Shirreff's bearded red," and "Pringle's
wheat." They have found wide acceptance, and the first two of them are
still considered by Vilmorin as belonging to the best wheats of France.
This second method of Shirreff evidently is quite analogous to the
principle of Lagasca and Le Couteur. The previous assumption that new
varieties with striking features were being produced by nature from time
to time, was abandoned, and a systematic inquiry into the worth of all
the divergent constituents of the fields was begun. Every single ear at
once proved to belong to a constant and pure race, but most of these
were only of average value. Some few however, excelled to a degree,
which made them worth multiplying, and to be introduced into trade as
separate varieties.
Once started, this new method of comparison, selection and isolated
multiplication was of course capable of many improvements. The culture
in the experiment-field was improved, so as to insure a fuller and more
rapid growth.
[115] The ripe heads had to be measured and counted and compared with
respect to their size and the number of their kernels. Qualities of
grain and of meal had to be considered, and the influence of climate and
soil could not be overlooked.
Concerning the real origin of his new types Shirreff seems never to have
been very inquisitive. He remarks that only the best cultivated
varieties have a chance to yield still better types, and that it is
useless to select and sow the best heads of minor sorts. He further
remarks that it is not probable that he found a new sport every time; on
the contrary he assumes that his selections had been present in the
field before, and during a series of succeeding generations. How many
years old they were, was of course impossible to determine. But there is
no reason to believe that the conditions in the fields of Scotland were
different from those observed on the Isle of Jersey by Le Couteur.
In the year 1862 Shirreff devoted himself to the selection of oats,
searching for the best panicles from the whole country, and comparing
their offspring in his experimental garden. "Early Fellow," "Fine
Fellow," "Longfellow" and "Early Angus" are very notable varieties
introduced into trade in this way.
[116] Some years later Patrick Shirreff described his experiments and
results in a paper entitled, "On the improvement of cereals," but the
descriptions are very short, and give few details of systematic value.
The leading principle, however, is clearly indicated, and anyone who
studies with care his method of working, may confidently attempt to
improve the varieties of his own locality in the same way.
This great principle of "variety-testing," as it has been founded by Le
Couteur and Patrick Shirreff, has increased in importance ever since.
Two main features are to be considered here. One is the production of
local races, the other the choice of the best starting-point for
hybridizing experiments, as is shown in California by the work of Luther
Burbank in crossing different elementary species of _Lilium pardalinum_
and others.
Every region and locality has its own conditions of climate and soil.
Any ordinary mixed race will contain some elementary forms which are
better adapted to a given district, while others are more suitable to
divergent conditions. Hence it can readily be inferred that the choice
cannot be the same for different regions. Every region should select its
own type from among the various forms, and variety testing therefore
becomes a task which every [117] one must undertake under his own
conditions. Some varieties will prove, after isolation, to be profitable
for large districts and perhaps for whole states. Others will be found
to be of more local value, but in such localities to excel all others.
As an example we may take one of the varieties of wheat originated by
the Minnesota Experiment Station. Hays described it as follows. It was
originated from a single plant. From among 400 plants of "Blue stem"
several of the best were chosen, each growing separately, a foot apart
in every direction. Each of the selected plants yielded 500 or more
grains of wheat, weighing 10 or more grams. The seeds from these
selected plants were raised for a few years until sufficient was
obtained to sow a plot. Then for several years the new strains were
grown in a field beside the parent-variety. One of them was so much
superior that all others were discarded. It was the one named "Minnesota
No. 169." For a large area of Minnesota this wheat seems capable of
yielding at least 1 or 2 bushels more grain per acre than its parent
variety, which is the best kind commonly and almost universally found on
the farms in southern and central Minnesota.
It would be quite superfluous for our present purpose to give more
instances. The fact of [118] the compound nature of so-called species of
cultivated plants seems to be beyond all doubt, and its practical
importance is quite obvious.
Acclimatization is another process, which is largely dependent on the
choice of adequate varieties. This is shown on a large scale by the slow
and gradual dispersion of the varieties of corn in this country. The
largest types are limited to temperate and subtropical regions, while
the varieties capable of cultivation in more northern latitudes are
smaller in size and stature and require a smaller number of days to
reach their full development from seed to seed. Northern varieties are
small and short lived, but the "Forty-day-corn" or "Quarantino maize" is
recorded to have existed in tropical America at the time of Columbus. In
preference, or rather to the entire exclusion of taller varieties, it
has thriven on the northern boundaries of the corn-growing states of
Europe since the very beginning of its cultivation.
According to Naudin, the same rule prevails with melons, cucumbers and
gherkins, and other instances could easily be given.
Referring now to the inferences that may be drawn from the experience of
the breeders in order to elucidate the natural processes, we will return
to the whitlow-grasses and pansies.
[119] Nature has constituted them as groups of slightly different
constant forms, quite in the same way as wheat and oats and corn.
Assuming that this happened ages ago somewhere in central Europe, it is
of course probable that the same differences in respect to the influence
of climatic conditions will have prevailed as with cereals. Subsequent
to the period which has produced the numerous elementary species of the
whitlow-grass came a period of widespread distribution. The process must
have been wholly comparable with that of acclimatization. Some species
must have been more adapted to northern climates, others to the soils of
western or eastern regions and so on. These qualities must have decided
the general lines of the distribution, and the species must have been
segregated according to their respective climatic qualities, and their
adaptability to soil and weather. A struggle for life and a natural
selection must have accompanied and guided the distribution, but there
is no reason to assume that the various forms were changed by this
process, and that we see them now endowed with other qualities than they
had at the outset.
Natural selection must have played, in this and in a large number of
other cases, quite the same part as the artificial method of variety
testing.
[120] Indeed it may be surmised that this has been its chief and
prominent function. Taking up again our metaphor of the sieve we can
assert that in such cases climate and soil exercise sifting action and
in this way the application of the metaphor becomes more definite. Of
course, next to the climate and soil in importance, come ecological
conditions, the vegetable and animal enemies of the plants and other
influences of the same nature.
In conclusion it is to be pointed out that this side of the problem of
natural selection and the struggle for life appears to offer the best
prospects for experimental, or for continued statistical inquiry. Direct
observations are possible and any comparison of numerical proportions of
species in succeeding years affords clear proof of the part it plays.
And above all, such observations can be made quite independently of
doubtful theoretical considerations about presumed changes of character.
The fact of natural selection is plain and it should be studied in its
most simple conditions.
[121]
C. RETROGRADE VARIETIES