Species and Varieties, Their Origin by Mutation Part 6

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 s.h.i.+rreff 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 a.s.sumes 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 s.h.i.+rreff 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 s.h.i.+rreff described his experiments and results in a paper ent.i.tled, "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 s.h.i.+rreff, 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 lat.i.tudes 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, cuc.u.mbers 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-gra.s.ses and pansies.

[119] Nature has const.i.tuted them as groups of slightly different constant forms, quite in the same way as wheat and oats and corn.

a.s.suming 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-gra.s.s 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 a.s.sume 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 a.s.sert 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

LECTURE V

CHARACTERS OF RETROGRADE VARIETIES

Every one admires the luxuriance of garden-flowers, and their diversity of color and form. All parts of the world have contributed to their number and every taste can find its preference among them. New forms produced by the skill of the breeder are introduced every year. This has been done mostly by crossing and intermingling the characters of introduced species of the same genus. In some of the cases the history of our flowers is so old that their hybrid origin is forgotten, as in the case of the pansies. Hybridizations are still going on in other groups on a large scale, and new forms are openly claimed to be of hybrid origin.

Breeders and amateurs generally have more interest in the results than in the way in which they have been brought about. Excellent flowers and fruit recommend themselves and there seems to be no reason for inquiring [122] about their origin. In some cases the name of the originator may be so widely known that it adds weight to the value of the new form, and therefore may advantageously be coupled with it. The origin and history of the greater part of our garden-flowers, fruits and vegetables are obscure; we see them as they are, and do not know from whence they came.

The original habitat for a whole genus or for a species at large, may be known, but questions as to the origin of the single forms, of which it is built up, ordinarily remain unanswered.

For these reasons we are restricted in most cases to the comparison of the forms before us. This comparison has led to the general use of the term "variety" in opposition to "species." The larger groups of forms, which are known to have been introduced as such are called species. All forms which by their characters belong to such a species are designated as varieties, irrespective of their systematic relation to the form, considered as the ancestor of the group.

Hence, we distinguish between "hybrid varieties" and "pure varieties"

according to their origin from different parents or from a single line of ancestors. Moreover, in both groups the forms may be propagated by seeds, or in the vegetative way by buds, by grafting or [123] by cutting, and this leads to the distinction of "seed-varieties" and "vegetative varieties." In the first case the inheritance of the special characters through the seeds decides the status of the variety, in the latter case this point is left wholly out of consideration.

Leaving aside all these different types, we are concerned here only with the "seed-varieties" of pure origin, or at least with those, that are supposed to be so. Hybridization and vegetative multiplication of the hybrids no doubt occur in nature, but they are very rare, when compared with the ordinary method of propagation by seed. "Seed-varieties" may further be divided into constant and inconstant ones. The difference is very essential, but the test is not always easy to apply. Constant varieties are as sharply defined and as narrowly limited as are the best wild species, while inconstant types are cultivated chiefly on account of their wide range of form and color. This diversity is repeated yearly, even from the purest seed. We will now discuss the constant seed-varieties, leaving the inconstant and eversporting types to a subsequent lecture.

In this way we may make an exact inquiry into the departures from the species which are ordinarily considered to const.i.tute the essential character of such a constant and pure seed-variety [124] and need only compare these differences with those that distinguish the elementary species of one and the same group from each other.

Two points are very striking. By far the greatest part of the ordinary garden-varieties differ from their species by a single sharp character only. In derivative cases two, three or even more such characters may be combined in one variety, for instance, a dwarfed variety of the larkspur may at the same time bear white flowers, or even double white flowers, but the individuality of the single characters is not in the least obscured by such combinations.

The second point is the almost general occurrence of the same variety in extended series of species. White and double flowers, variegated leaves, dwarfs and many other instances may be cited. It is precisely this universal repet.i.tion of the same character that strikes us as the essential feature of a variety.

And again these two characteristics may now be considered separately.

Let us begin with the sharpness of the varietal characters. In this respect varieties differ most obviously from elementary species. These are distinguished from their nearest allies in almost all organs. There is no prominent distinctive feature between the single forms of _Draba_ [125] _Verna_, _Helianthemum_ or of _Taraxac.u.m_; all characters are almost equally concerned. The elementary species of _Draba_ are characterized, as we have seen, by the forms and the hairiness of the leaves, the number and height of the flower-stalks, the breadth and incision of the petals, the forms of the fruits, and so on. Every one of the two hundred forms included in this collective species has its own type, which it is impossible to express by a single term. Their names are chosen arbitrarily. Quite the contrary is the case with most of the varieties, for which one word ordinarily suffices to express the whole difference.

White varieties of species with red or blue flowers are the most common instances. If the species has a compound color and if only one of the const.i.tuents is lost, partially colored types arise as in _Agrostemma Coronaria bicolor_. Or the spots may disappear and the color become uniform as in _Gentiana punctata concolor_ and the spotless Arum or _Arum maculatum immaculatum_. Absence of hairs produces forms as _Biscutella laevigata glabra_; lack of p.r.i.c.kles gives the varieties known as _inermis, as for instance, _Ranunculus arvensis inermis_.

_Cytisus prostratus_ has a variety _ciliata_, and _Solanum Dulcamara_, or the bitter-sweet, has a variety called _tomentosum_. The curious monophyllous [126] variety of the strawberry and many other forms will be discussed later.

To enlarge this list it would only be necessary to extract from a flora, or from a catalogue of horticultural plants, the names of the varieties enumerated therein. In nearly every instance, where true varieties and not elementary species are concerned, a single term expresses the whole character.

Such a list would also serve to ill.u.s.trate the second point since the same names would recur frequently. Long lists of varieties are called alba, or inermis, or canescens or lutea, and many genera contain the same appellations. In some instances the systematists use a diversity of names to convey exactly the same idea, as if to conceal the monotony of the character, as for instance in the case of the lack of hairs, which is expressed by the varietal names of _Papaver dubium glabrum_, _Arabis ciliata glabrata_, _Arabis hirsuta glaberrima_, _Veronica spicata nitens_, _Amygdalus persica laevis_, _Paeonia corallina Leiocarpa_, &c.

On the contrary we find elementary species in different genera based on the greatest possible diversity of features. The forms of _Taraxac.u.m_ or _Helianthemum_ do not repeat those of _Draba_ or _Viola_. In roses and brambles the distinguis.h.i.+ng features are characteristic of the type, as [127] they are evidently derived from it and limited to it. And this is so true that n.o.body claims the grade of elementary species for white roses or white brambles, but everyone recognizes that forms diverging from the nearest species by a single character only, are to be regarded as varieties.

This general conviction is the basis on which we may build up a more sharply defined distinction between elementary species and varieties. It is an old rule in systematic botany, that no form is to be const.i.tuted a species upon the basis of a single character. All authors agree on this point; specific differences are derived from the totality of the attributes, not from one organ or one quality. This rule is intimately connected with the idea that varieties are derived from species. The species is the typical, really existing form from which the variety has originated by a definite change. In enumerating the different forms the species is distinguished by the term of genuine or typical, often only indicated as _a_ or the first; then follow the varieties sometimes in order of their degree of difference, sometimes simply in alphabetical order. In the case of elementary species there is no real type; no one of them predominates because all are considered to be equal in rank, and the systematic species to which they [128] are referred is not a really existing form, but is the abstraction of the common type of all, just as it is in the case of a genus or of a family.

Summarizing the main points of this discussion, we find that elementary species are of equal rank and together build up the collective or systematic ideal species. Varieties on the other hand are derived from a real and commonly, still existing type.

I hope that I have succeeded in showing that the difference between elementary species, or, as they are often called, smaller or subspecies, on the one hand and varieties on the other, is quite a marked one.

However, in order to recognize this principle it is necessary to limit the term variety, to those propagating themselves by seed and are of pure and not of hybrid origin.

But the principle as stated here, does not involve an absolute contrast between two groups of characters. It is more a difference in our knowledge and appreciation of them than a difference in the things themselves. The characters of elementary species are, as a rule, new to us, while those of varieties are old and familiar. It seems to me that this is the essential point.

And what is it that makes us familiar with them? Obviously the continuous recurrence of the same changes, because by a constant repet.i.tion they must of course lose their novelty.

[129] Presently we shall look into these characters more in detail and then we shall find that they are not so simple as might be supposed at first sight; but precisely because we are so familiar with them, we readily see that their different features really belong to a single character; while in elementary species everything is so new that it is impossible for us to discern the unities of the new attributes.

If we bear in mind all these difficulties we cannot wonder at the confusion on this question that seems to prevail everywhere. Some authors following Linnaeus simply call all the subdivisions of species, varieties; others follow Jordan and avoid the difficulty by designating all smaller forms directly as species. The ablest systematists prefer to consider the ordinary species as collective groups, calling their const.i.tuents "The elements of the species," as was done by A.P. De Candolle, Alph. De Candolle and Lindley.

By this method they clearly point out the difference between the subdivisions of wild species as they ordinarily occur, and the varieties in our gardens, which would be very rare, were they not singled out and preserved.

Our familiarity with a character and our grounds for calling it an old acquaintance may result from two causes, which in judging a new [130]

variety are essentially different. The character in question may be present in the given species or it may be lacking, but present in the other group. In the first case a variety can only be formed by the loss of the character, in the second case it arises by the addition of a new one.

The first mode may be called a negative process, while the second is then to be designated as positive. And as it is more easy to lose what one has than to obtain something new, negative varieties are much more common than are positive ones.