Chapter 19

It is worth while to dwell a moment on the capacity of the individuals with red flowers to reproduce the striped type among their offspring. For it is manifest that this latter quality must have lain dormant in them during their whole life. Darwin has already pointed out that when a character of a grandparent, which is wanting in the progeny, reappears in the second generation, this quality must always be assumed to have been present though latent in the intermediate generation. To the many instances given by him of such alternative inheritance, the monochromatic reversionists of the striped varieties are to be added as a new type. It is moreover, a very suggestive type, since the latency is manifestly of quite another character than for instance in the case of Mendelian hybrids, and probably more allied to those instances, [325] where secondary sexual marks, which are as a rule only evolved by one sex, are transferred to the offspring through the other.

Stripes are by no means limited to flowers. They may affect the whole foliage, or the fruits and the seeds, and even the roots. But all such cases occur much more rarely than the striped flowers. An interesting instance of striped roots is afforded by radishes. White and red varieties of different shapes are cultivated. Besides them sometimes a curious motley sort may be seen in the markets, which is white with red spots, which are few and narrow in some samples, and more numerous and broader in others. But what is very peculiar and striking is the circumstance, that these stripes do not extend in a longitudinal, but in a transverse direction. Obviously this must be the effect of the very notable growth in thickness. Assuming that the colored regions were small in the beginning, they must have been drawn out during the process of thickening of the root, and changed into transverse lines. Rarely a streak may have had its greatest extension in a transverse direction from the beginning, in which case it would only be broadened and not definitely changed in its direction.

This variety being a very fine one, and more agreeable to the eye than the uniform colors, is [326] being more largely cultivated in some countries. It has one great drawback: it never comes wholly true from seed. It may be grown in full isolation, and carefully selected, all red or nearly monochromatic samples being rooted out long before blooming, but nevertheless the seed will always produce some red roots. The most careful selection, pursued through a number of years, has not been sufficient to get rid of this regular occurrence of reversionary individuals. Seed-growers receive many complaints from their clients on this account, but they are not able to remove the difficulty. This experience is in full agreement with the experimental evidence given by the snapdragon, and it would certainly be very interesting to make a complete pedigree-culture with the radishes to test definitely their compliance with the rules observed for striped flowers.

Horticulturists in such cases are in the habit of limiting themselves to the sale of so-called mixed seeds. From these no client expects purity, and the normal and hereditary diversity of types is here in some sense concealed under the impurities included in the mixture from lack of selection. Such cases invite scrutiny, and would, no doubt, with the methods of isolation, artificial pollination, and the sowing of the seeds separately from each parent, yield [327] results of great scientific value. Any one who has a garden, and sufficient perseverance to make pure cultures during a series of years might make important contributions to scientific knowledge in this way.

Choice might be made from among a wide range of different types. A variety of corn called "Harlequin" shows stripes on its kernels, and one ear may offer nearly white and nearly red seeds and all the possible intermediate steps between them. From these seeds the next generation will repeat the motley ears, but some specimens will produce ears of uniform kernels of a dark purple, showing thus the ordinary way of reversion. Some varieties of beans have spotted seeds, and among a lot of them one may be sure to find some purely red ones. It remains to be investigated what will be their offspring, and whether they are due to partial or to individual variation.

The cockscomb (_Celosia cristata_) has varieties of nearly all colors from white and yellow to red and orange, and besides them some striped varieties occur in our gardens, with the stripes going from the lower parts of the stem up to the very crest of the comb. They are on sale as constant varieties, but nothing has as yet been recorded concerning their peculiar behavior in the inheritance of the stripes. [328] Striped grapes, apples and other fruits might be mentioned in this connection.

Before leaving the striped varieties, attention is called to an interesting deduction, which probably gives an explanation of one of the most widely known instances of ever-sporting garden plants. Striped races always include two types. Both of them are fertile, and each of them reproduces in its offspring both its own and the alternate type. It is like a game of ball, in which the opposing parties always return the ball. But now suppose that only one of the types were fertile and the other for some reason wholly sterile, and assume the reversionary, or primitive monochromatic individuals to be fertile, and the derivative striped specimens to bloom without seed. If this were the case, knowledge concerning the hereditary qualities would be greatly limited. In fact the whole pedigree would be reduced to a monochromatic strain, which would in each generation sport in some individuals into the striped variety. But, being sterile, they would not be able to propagate themselves.

Such seems to be the case with the double flowered stocks. Their double flowers produce neither stamens nor pistils, and as each individual is either double or single in all its flowers, the doubles are wholly destitute of seed. [329] Nevertheless, they are only reproduced by seed from single flowers, being an annual or biennial species.

Stocks are a large family, and include a wonderful variety of colors, ranging from white and yellow to purple and red, and with some variations toward blue. They exhibit also diversity in the habit of growth. Some are annuals, including the ten-week and pyramidal forms; others are intermediates and are suitable for pot-culture; and the biennial sorts include the well-known "Brompton" and "Queen" varieties. Some are large and others are small or dwarf. For their brightness, durability and fragrance, they are deservedly popular. There are even some striped varieties. Horticulturists and amateurs generally know that seed can be obtained from single stocks only, and that the double flowers never produce any. It is not difficult to choose single plants that will produce a large percentage of double blossoms in the following generation. But only a percentage, for the experiments of the most skilled growers have never enabled them to save seed, which would result entirely in double flowering plants. Each generation in its turn is a motley assembly of singles and doubles.

Before looking closer into the hereditary peculiarities of this old and interesting ever-sporting [330] variety, it may be as well to give a short description of the plants with double flowers. Generally speaking there are two principal types of doubles. One is by the conversion of stamens into petals, and the other is an anomaly, known under the name of _petalomany_.

The change of stamens into petals is a gradual modification. All intermediate steps are easily to be found. In some flowers all stamens may be enlarged, in others only part of them. Often the broadened filaments bear one or two fertile anthers. The fertility is no doubt diminished, but not wholly destroyed. Individual specimens may occur, which cannot produce any seed, but then others of the same lot may be as fertile as can be desired. As a whole, such double varieties are regularly propagated by seed.

Petalomany is the tendency of the axis of some flowers never to make any stamens or pistils, not even in altered or rudimentary form. Instead of these, they simply continue producing petals, going on with this production without any other limit than the supply of available food. Numerous petals fill the entire space within the outer rays, and in the heart of the flower innumerable young ones are developed half-way, not obtaining food enough to attain [331] full size. Absolute sterility is the natural consequence of this state of things.

Hence it is impossible to have races of petalomanous types. If the abnormality happens to show itself in a species, which normally propagates itself in an asexual way, the type may become a vegetative variety, and be multiplied by bulbs, buds or cuttings, etc. Some cultivated anemones and crowfoots (_Ranunculus_) are of this character, and even the marsh-marigold (_Caltha palustris_) has a petalomanous variety. I once found in a meadow such a form of the meadow-buttercup (_Ranunculus_ acris_), and succeeded in keeping it in my garden for several years, but it did not make seeds and finally died. Camellias are known to have both types of double flowers. The petalomanous type is highly regular in structure, so much so as to be too uniform in all its parts to be pleasing, while the conversion of stamens into petals in the alternative varieties gives to these flowers a more lively diversity of structure. Lilies have a variety called _Lilium candidum flore pleno_, in which the flowers seem to be converted into a long spike of bright, white narrow bracts, crowded on an axis which never seems to cease their production.

It is manifestly impossible to decide how all such sterile double flowers have originated. [332] Perhaps each of them originally had a congruent single-flowered form, from which it was produced by seed in the same way as the double stocks now are yearly. If this assumption is right, the corresponding fertile line is now lost; it has perhaps died out, or been masked. But it is not absolutely impossible that such strains might one day be discovered for one or another of these now sterile varieties.

Returning to the stocks we are led to the conception that some varieties are absolutely single, while others consist of both single-flowered and double-flowered individuals. The single varieties are in respect to this character true to the original wild type. They never give seed which results in doubles, providing all intercrossing is excluded. The other varieties are ever-sporting, in the sense of this term previously assumed, but with the restriction that the sports are exclusively one-sided, and never return, owing to their absolute sterility.

The oldest double varieties of stocks have attained an age of a century and more. During all this time they have had a continuous pedigree of fertile and single-flowered individuals, throwing off in each generation a definite number of doubles. This ratio is not at all dependent on chance or accident, nor is it even variable to a remarkable degree. Quite on the contrary [333] it is always the same, or nearly the same, and it is to be considered as an inherent quality of the race. If left to themselves, the single individuals always produce singles and doubles in the same quantity; if cultivated after some special method, the proportion may be slightly changed, bringing the proportion of doubles up to 60% or even more.

Ordinarily the single and double members of such a race are quite equal in the remainder of their attributes, especially in the color of their flowers. But this is not always the case. The colors of such a race may repeat for themselves the peculiarities of the ever-sporting characters. It often happens that one color is more or less strictly allied to the doubles, and another to the singles. This sometimes makes it difficult to keep the various colors true. There are certain sorts, which invariably exhibit a difference in color between the single and the double flowers. The sulphur-yellow varieties may be adduced as illustrative examples, because in them the single flowers always come white. Hence in saving seed, it is impossible so to select the plant, that an occasional white does not also appear among the double flowers, agreeing in this deviation with the general rule of the eversporting varieties.

I commend all the above instances to those [334] who wish to make pedigree-cultures. The cooperation of many is needed to bring about any notable advancement, since the best way to secure isolation is to restrict one's self to the culture of one strain, so as to avoid the intermixture of others. So many facts remain doubtful and open to investigation, that almost any lot of purchased seed may become the starting point for interesting researches. Among these the sulphur-yellow varieties should be considered in the first place.

In respect to the great questions of heredity, the stocks offer many points of interest. Some of these features I will now try to describe, in order to show what still remains to be done, and in what manner the stocks may clear the way for the study of the ever-sporting varieties.

The first point, is the question, which seeds become double-flowered and which single-flowered plants? Beyond all doubt, the determination has taken place before the ripening of the seed. But though the color of the seed is often indicative of the color of the flowers, as in some red or purple varieties, and though in balsams and some other instances the most "highly doubled" flowers are to be obtained from the biggest and plumpest seeds, no such rule seems to exist respecting the double stocks. Now if one half of the seeds gives doubles, and [335] the other half singles, the question arises, where are the singles and the doubles to be found on the parent-plant?

The answer is partly given by the following experiment. Starting from the general rule of the great influence of nutrition on variability, it may be assumed that those seeds will give most doubles, that are best fed. Now it is manifest that the stem and larger branches are, in a better condition than the smaller twigs, and that likewise the first fruits have better chances than the ones formed later. Even in the same pod the uppermost seeds will be in a comparatively disadvantageous position. This conception leads to an experiment which is the basis of a practical method much used in France in order to get a higher percentage of seeds of double-flowering plants.

This method consists in cutting off, in the first place the upper parts of all the larger spikes, in the second place, the upper third part of each pod, and lastly all the small and weak twigs. In doing so the percentage is claimed to go up to 67-70%, and in some instances even higher. This operation is to be performed as soon as the required number of flowers have ceased blossoming. All the nutrient materials, destined for the seeds, are now forced to flow into these relatively few embryos, and it is clear that [336] they will be far better nourished than if no operation were made.

In order to control this experiment some breeders have made the operation on the fruits when ripe, instead of on the young pods, and have saved the seeds from the upper parts separately. This seed, produced in abundance, was found to be very poor in double flowers, containing only some 20-30%. On the contrary the percentage of doubles in the seed of the lower parts was somewhat augmented, and the average of both would have given the normal proportion of 50%.

Opposed to the French method is the German practice of cultivating stocks, as I have seen it used on a very large scale at Erfurt and at other places. The stocks are grown in pots on small scaffolds, and not put on or into the earth. The obvious aim of this practice is to keep the earth in the pots dry, and accordingly they are only scantily watered. In consequence they cannot develop as fully as they would have done when planted directly in the beds, and they produce only small racemes and no weak twigs, eliminating thereby without further operation the weaker seeds as by the French method. The effect is increased by planting from 6-10 separate plants in each pot.

It would be very interesting to make comparative [337] trials of both methods, in order to discover the true relation between the practice and the results reached. Bath should also be compared with cultures on open plots, which are said to give only 50% of doubles. This last method of culture is practiced wherever it is desired to produce great quantities of seeds at a low cost. Such trials would no doubt give an insight into the relations of hereditary characters to the distribution of the food within the plant.

A second point is the proportional increase of the double-flowering seeds with age. If seed is kept for two or three years, the greater part of the grains will gradually die, and among the remainder there is found on sowing, a higher percentage of double ones. Hence we may infer that the single-flowered seeds are shorter lived than the doubles, and this obviously points to a greater weakness of the first. It is quite evident that there is some common cause for these facts and for the above cited experience, that the first and best pods give more doubles. Much, however, remains to be investigated before a satisfactory answer can be made to these questions.

A third point is the curious practice, called by the French "esimpler," and which consists in pulling out the singles when very young. It seems to be done at an age when the flower-buds [338] are not yet visible, or at least are not far enough developed to show the real distinctive marks. Children may be employed to choose and destroy the singles. There are some slight differences in the fullness and roundness of the buds and the pubescence of the young leaves. Moreover the buds of the doubles are said to be sweeter to the taste than those of the singles. But as yet I have not been able to ascertain, whether any scientific investigation of this process has ever been made, though according to some communications made to me by the late Mr. Cornu, the practice seems to be very general in the environs of Paris. In summer large fields may be seen, bearing exclusively double flowers, owing to the weeding out of the singles long before flowering.

Bud-variation is the last point to be taken up. It seems to be very rare with stocks, but some instances have been recorded in literature. Darwin mentions a double stock with a branch bearing single flowers, and other cases are known to have occurred. But in no instance does the seed of such a bud-variant seem to have been saved. Occasionally other reversions also occur. From time to time specimens appear with more luxurious growth and with divergent instead of erect pods. They are called, in Erfurt, "generals" on account [339] of their stiff and erect appearance, and they are marked by more divergent horns crowning the pods. They are said to produce only a relatively small number of doubles from their seeds, and even this small number might be due to fertilization with pollen of their neighbors. I saw some of these reversionary types; when inspecting the nurseries of Erfurt, but as they are, as a rule, thrown out before ripening their seed, nothing is exactly known about their real hereditary qualities.

Much remains to be cleared up, but it seems that one of the best means to find a way through the bewildering maze of the phenomena of inheritance, is to make groups of related forms and to draw conclusions from a comparison of the members of such groups. Such comparisons must obviously give rise to questions, which in their turn will directly lead to experimental investigation.

[340]

LECTURE XII

FIVE-LEAVED CLOVER

Every one knows the "four-leaved" clover. It is occasionally found on lawns, in pastures and by the roadsides. Specimens with five leaflets may be found now and then in the same place, or on the same plant, but these are rarer. I have often seen isolated plants with quaternate leaves, but only rarely have I observed individuals with more than one such leaf.

The two cases are essentially dissimilar. They may appear to differ but little morphologically, but from the point of view of heredity they are quite different. Isolated quaternate leaves are of but little interest, while the occurrence of many on the same individual indicates a distinct variety. In making experiments upon this point it is necessary to transplant the divergent individuals to a garden in order to furnish them proper cultural conditions and to keep them under constant observation. When a plant bearing a quaternate leaf is thus transplanted however, it rarely repeats the [341] anomaly. But when plants with two or more quaternate leaves on the same individual are chosen it indicates that it belongs to a definite race, which under suitable conditions may prove to become very rich in the anomalies in question.

Obviously it is not always easy to decide definitely whether a given individual belongs to such a race or not. Many trials may be necessary to secure the special race. I had the good fortune to find two plants of clover, bearing one quinate and several quaternate leaves, on an excursion in the neighborhood of Loosdrecht in Holland. After transplanting them into my garden, I cultivated them during three years and observed a slowly increasing number of anomalous leaves. This number in one summer amounted to 46 quaternate and 16 quinate leaves, and it was evident that I had secured an instance of the rare "five-leaved" race which I am about to describe.

Before doing so it seems desirable to look somewhat closer into the morphological features of the problem. Pinnate and palmate leaves often vary in the number of their parts. This variability is generally of the nature of a common fluctuation, the deviations grouping themselves around an average type in the ordinary way. Ash leaves bear five pairs, and [342] the mountain-ash (_Sorbus Aucuparia_) has six pairs of leaflets in addition to the terminal one. But this number varies slightly, the weaker leaves having less, the stronger more pairs than the average. Such however, is not the case, with ternate leaves, which seem to be quite constant. Four leaflets occur so very rarely that one seems justified in regarding them rather as an anomaly than, as a fluctuation. And this is confirmed by the almost universal absence of two-bladed clover-leaves.

Considering the deviation as an anomaly, we may look into its nature. Such an inquiry shows that the supernumerary leaflets owe their origin to a splitting of one or more of the normal ones. This splitting is not terminal, as is often the case with other species, and as it may be seen sometimes in the clover. It is for the most part lateral. One of the lateral nerves grows out becoming a median nerve of the new leaflet. Intermediate steps are not wanting, though rare, and they show a gradual separation of some lateral part of a leaflet, until this division reaches the base and divides the leaflet into two almost equal parts. If this splitting occurs in one leaflet we get the "four-leaved" Clover, if it occurs in two there will be five leaflets. And if, besides this, the terminal leaflet produces a derivative on one or both of its sides, [343] we obtain a crown of six or seven leaflets on one stalk. Such were often met with in the race I had under cultivation, but as a rule it did not exceed this limit.