Chapter 23

In conclusion something is to be said about the choice of the seed. Obviously it is possible to compare seeds of different origin by sowing and treating them in the same way, giving attention to all the points above mentioned. In doing so the first question will be, whether there is a difference between the seeds of strong plants with a bright crown around the head and those of weaker individuals with lesser development of the anomaly. It is evident that such a difference must be expected, since the nutrition of the seed takes place during the period of the greatest sensitiveness.

But the experiments will show whether this effect holds good against the influences which tend to change the direction of the development of the anomaly during the time of germination. [398] The result of my attempt has shown that the choice of the seeds has a manifest influence upon the ultimate development of the monstrosity, but that this influence is not strong enough to overwhelm all other factors.

The choice of the fullest or smallest crowns may be repeated during succeeding generations, and each time compared with a culture under average conditions. By this means we come to true selection-experiments, and these result in a notable and rapid change of the whole strain. By selecting the brightest crowns I have come up in three years from 40 to 90 and ultimately to 120 converted stamens in the best flower of my culture, and in selecting the smallest crowns I was able in three years to exclude nearly all good crowns, and to make cultures in which heads with less than half-filled crowns constituted the majority. But such selected strains always remain very sensitive to treatment, and by changing the conditions the effect may be wholly lost in a single year, or even turned in the contrary direction. In other words, the anomaly is more dependent on external conditions during the germinating period than on the choice of the seeds, providing these belong to the pistilloid variety and have not deteriorated by some crossing with other sorts.

At the beginning of this lecture I stated that [399] no selection is adequate to produce either a pure strain of brightly crowned flower-heads without atavism, or to conduce to an absolute and permanent loss of the anomaly. During a series of years I have tested my plants in both directions, but without the least effect. Limits are soon reached on both sides, and to transgress these seems quite impossible.

Taking these limits as the marks of the variety, and considering all fluctuations between them as responses to external influences working during the life of the individual or governing the ripening of the seeds, we get a clear picture of a permanent ever-sporting type. The limits are absolutely permanent during the whole existence of this already old variety. They never change. But they include so wide a range of variability, that the extremes may be said to sport into one another, so much the more so as one of the extremes is to be considered morphologically as the type of the variation, while the other extreme can hardly be distinguished from the normal form of the species.

[400]

LECTURE XIV

MONSTROSITIES

I have previously dealt with the question of the hereditary tendencies that cause monstrosities. These tendencies are not always identical for the same anomaly. Two different types may generally, be distinguished. One of them constitutes a poor variety, the other a rich one. But this latter is abundant and the first one is poor in instances of exactly the same conformation. Therefore the difference only lies in the frequency of the anomaly, and not in its visible features. In discovering an instance of any anomaly it is therefore impossible to tell whether it belongs to a poor or to a rich race. This important question can only be answered by direct sowing-experiments to determine the degree of heredity.

Monstrosities are often considered as accidents, and rightfully so, at least as long as they are considered from a morphological point of view. Physiology of course excludes all accidentality. And in our present ease it shows [401] that some internal hereditary quality is present, though often latent, and that the observed anomalies are to be regarded as responses of this innate tendency to external conditions. Our two types differ in the frequency of these responses. Rare in the poor race, they are numerous in the rich variety. The external conditions being the same for both, the hereditary factor must be different. The tendency is weak in the one and strong in the other. In both cases, according to my experience, it may be weakened or strengthened by selection and by treatment. Often to a very remarkable degree, but not so far as to transgress the limits between the two races. Such transgression may apparently be met with from time to time, but then the next generation generally shows the fallacy of the conclusion, as it returns more or less directly to the type from which the strain had been derived. Monstrosities should always be studied by physiologists from this point of view. Poor and rich strains of the same anomaly seem at first sight to be so nearly allied that it might be thought to be very easy to change the one into the other. Nevertheless such changes are not on record, and although I have made several attempts in this line, I never succeeded in passing the limit. I am quite convinced that sometime [402] a method will be discovered of arbitrarily producing such conversions, and perhaps the easiest way to attain artificial mutations may lie concealed here. But as yet not the slightest indication of this possibility is to be found, save the fallacious conclusions drawn from too superficial observations.

Unfortunately the poor strains are not very interesting. Their chance of producing beautiful instances of the anomaly for which they are cultivated is too small. Exceptions to this rule are only afforded by those curious and rare anomalies, which command general attention, and of which, therefore, instances are always welcome. In such cases they are searched for with perseverance, and the fact of their rarity impresses itself strongly on our mind.

Twisted stems are selected as a first example. This monstrosity, called _biastrepsis_, consists of strongly marked torsions as are seen in many species with decussate leaves, though as a rule it is very rare. Two instances are the most generally known, those of the wild valerian (_Valeriana officinalis_) and those of cultivated and wild sorts of teasels (_Dipsacus fullonum_, _D. sylvestris_, and others). Both of these I have cultivated during upwards of fifteen years, but with contradictory results. The valerian is a perennial herb, multiplying itself yearly by [403] slender rootstocks or runners producing at their tips new rosettes of leaves and in the center of these the flowering stem. My original plant has since been propagated in this manner, and during several years I preserved large beds with hundreds of stems, in others I was compelled to keep my culture within more restricted limits. This plant has produced twisted stems of the curious shape, with a nearly straight flag of leaves on one side, described by De Candolle and other observers, nearly every year. But only one or two instances of abnormal stems occurred in each year, and no treatment has been found that proved adequate to increase this number in any appreciable manner. I have sown the seeds of this plant repeatedly, either from normal or from twisted stems, but without better results. It was highly desirable to be able to offer instances of this rare and interesting peculiarity to other universities and museums, but no improvement of the race could be reached and I have been constrained to give it up. My twisted valerian is a poor race, and hardly anything can be done with it. Perhaps, in other countries the corresponding rich race may be hidden somewhere, but I have never had the good fortune of finding it.

This good fortune however, I did have with the wild teasel or _Dipsacus sylvestris_. [404] Stems of this and of allied species are often met with and have been described by several writers, but they were always considered as accidents and nobody had ever tried to cultivate them. In the summer of 1885 I saw among a lot of normal wild teasels, two nicely twisted stems in the botanical garden of Amsterdam. I at once proposed to ascertain whether they would yield a hereditary race and had all the normal individuals thrown away before the flowering time. My two plants flowered in this isolated condition and were richly pollinated by insects. Of course, at that time, I knew nothing of the dependency of monstrosities on external conditions, and made the mistake of sowing the seeds and cultivating the next generation in too great numbers on a small space. But nevertheless the anomaly was repeated, and the aberrant individuals were once more isolated before flowering. The third generation repeated the second, but produced sixty twisted stems on some 1,600 individuals. The result was very striking and quite sufficient for all further researches, but the normal condition of the race was not reached. This was the case only after I had discovered the bad effects of growing too many plants in a limited space. In the fourth generation I restricted my whole culture to about 100 individuals, and by this simple [405] means at once got up to 34% of twisted stems. This proportion has since remained practically the same. I have selected and isolated my plants during five succeeding generations, but without any further result, the percentage of twisted stems fluctuating between 30 and about 45 according to the size of the cultures and the favorableness or unfavorableness of the weather.

It is very interesting to note that all depends on the question whether one has the good fortune of finding a rich race or not, as this pedigree-culture shows. Afterwards everything depends on treatment and very little on selection. As soon as the treatment becomes adequate, the full strength of the race at once displays itself, but afterwards no selection is able to improve it to any appreciable amount. Of course, in the long run, the responses will be the same as those of the pistilloid poppies on the average, and some influence of selection will show itself on closer scrutiny.

Compared with the polycephalous poppies my race of twisted teasels is much richer in atavists. They are never absent, and always constitute a large part of each generation and each bed, comprising somewhat more than half of the individuals. Intermediate stages between them and the wholly twisted stems are not wanting, [406] and a whole series of steps may easily be observed from sufficiently large cultures. But they are always relatively rare, and any lot of plants conveys the idea of a dimorphous race, the small twisted stems contrasting strongly with the tall straight ones.

A sharper contrast between good representatives of a race and their atavists is perhaps to be seen in no other instance. All the details contribute to the differentiation in appearance. The whole stature of the plants is affected by the varietal mark. The atavists are not, as in the case of the poppies, obviously allied with the type by a full range of intermediate steps, but quite distant from it by their rarity. There seems to be a gap in the same way as between the striped flowers of the snapdragon and their uniform red atavists, while with the poppies the atavists may be viewed as being only the extremes of a series of variations fluctuating around some average type.

From this reason it is as interesting to appreciate the hereditary position of the atavists of twisted varieties as it was for the red-flowered descendants of the striped flowers. In order to ascertain this relation it is only necessary to isolate some of them during the blooming-period. I made this experiment in the summer of 1900 with the eighth generation of my race, and contrived [407] to isolate three groups of plants by the use of parchment bags, covering them alternately, so the flowers of only one group were accessible to insects, at a time. I made three groups, because the atavists show two different types. Some specimens have decussate stems, others bear all their leaves in whorls of three, but in respect to the hereditary tendency of the twisting character this difference does not seem to be of any importance.

In this way I got three lots of seeds and sowed enough of them to have three groups of plants each containing about 150-200 well developed stems. Among these I counted the twisted individuals, and found nearly the same numbers for all three. The twisted parents gave as many as 41% twisted children, but the decussate atavists gave even somewhat more, viz., 44%, while the ternate specimens gave 37%. Obviously the divergences between these figures are too slight to be dwelt upon, but the fact that the atavists are as true or nearly as true inheritors of the twisted race as the best selected individuals is clearly proved by this experience.

It is evident that here we have a double race, including two types, which may be combined in different degrees. These combinations determine a wide range of changes in the stature of the plants, and it seems hardly right to use the [408] same term for such changes as for common variations. It is more a contention of opposite characters than a true phenomenon of simple variability. Or perhaps we might say that it is the effect of the cooperation of a very variable mark, the twisting, with a scarcely varying attribute of the normal structure of the stem. Between the two types an endless diversity prevails, but outwardly there are limits which are never transgressed. The double race is as permanent, and in this sense as constant, as any ordinary simple variety, both in external form, and in its intimate hereditary qualities.

I have succeeded in discovering some other rich races of twisted plants. One of them is the Sweet William (_Dianthus barbatus_), which yielded, after isolation, in the second generation, 25% of individuals with twisted stems, and as each individual produces often 10 and more stems, I had a harvest of more than half a thousand of instances of this curious, and ordinarily very rare anomaly. My other race is a twisted variety of _Viscaria oculata_, which is still in cultivation, as it has the very consistent quality of being an annual. It yielded last summer (1903) as high a percentage as 65 of twisted individuals, many of them repeating the monstrosity on several branches. After some occasional observations _Gypsophila paniculata_ [409] seems to promise similar results. On the other hand I have sowed in vain the seeds of twisted specimens of the soapwort and the cleavewort (_Saponaria officinalis_ and _Galium Aparine_). These and some others seem to belong to the same group as the valerian and to constitute only poor or so-called half-races.

Next to the torsions come the fasciated stems. This is one of the most common of all malformations, and consists, in its ordinary form, of a flat ribbon-like expansion of the stems or branches. Below they are cylindrical, but they gradually lose this form and assume a flattened condition. Sometimes the rate of growth is unequal on different portions or on the opposite sides of the ribbon, and curvatures are produced and these often give to the fasciation a form that might be compared with a shepherd's crook. It is a common thing for fasciated branches and stems to divide at the summit into a number of subdivisions, and ordinarily this splitting occurs in the lower part, sometimes dividing the entire fasciated portion. In biennial species the rosette of the root-leaves of the first year may become changed by the monstrosity, the heart stretching in a transverse direction so as to become linear. In the next year this line becomes the base from which the stem grows. In such cases the fasciated stems [410] are broadened and flattened from the very beginning, and often retain the incipient breadth throughout their further development. Species of primroses (_Primula japonica_ and others), of buttercups (_Ranunculus bulbosus_), the rough hawksbeard (_Crepis biennis_), the Aster _Tripolium_, and many others could be given as instances.

Some of these are so rare as to be considered as poor races, and in cultural trials do not produce the anomaly except in a very few instances. Heads of rye are found in a cleft condition from time to time, single at their base and double at the top, but this anomaly is only exceptionally repeated from seed. Flattened stems of _Rubia tinctorum_ are not unfrequently met with on the fields, but they seem to have as little hereditary tendency as the split rye (_Secale Cereale_). Many other instances could be given. Both in the native localities and in pedigree-cultures such ribboned stems are only seen from time to time, in successive years, in annual and biennial as well as in perennial species. The purple pedicularis (_Pedicularis palustris_) in the wild state, and the sunflower among cultivated plants, may be cited instead of giving a long list of analogous instances.

On the other hand rich races of flattened stems are not entirely lacking. They easily betray [411] themselves by the frequency of the anomaly, and therefore may be found, and tried in the garden. Under adequate cultivation they are here as rich in aberrant individuals as the twisted races quoted above, producing in good years from 30-40% and often more instances. I have cultivated such rich races of the dandelion (_Taraxacum officinale_), of _Thrincia hirta_, of the dame's violet (_Hesperis matronalis_), of the hawkweed (_Picris hieracioides_), of the rough hawksbeard (_Crepis biennis_), and others.

Respecting the hereditary tendencies these rich varieties with flattened stems may be put in the same category with the twisted races. Two points however, seem to be of especial interest and to deserve a separate treatment.

The common cockscomb or _Celosia cristata_, one of the oldest and most widely cultivated fasciated varieties may be used to illustrate the first point. In beds it is often to be seen in quite uniform lots of large and beautiful crests, but this uniformity is only secured by careful culture and selection of the best individuals. In experimental trials such selection must be avoided, and in doing so a wide range of variability at once shows itself. Tall, branched stems with fan-shaped tops arise, constituting a series of steps towards complete atavism. This last [412] however, is not to be reached easily. It often requires several successive generations grown from seed collected from the most atavistic specimens. And even such selected strains are always reverting to the crested type. There is no transgression, no springing over into a purely atavistic form, such as may be supposed to have once been the ancestor of the present cockscomb. The variety includes crests and atavists, and may be perpetuated from both. Obviously every gardener would select the seeds of the brightest crests, but with care the full crests may be recovered, even from the worst reversionists in two or three generations. It is a double race of quite the same constitution as the twisted teasels.

My second point is a direct proof of this assertion, but made with a fasciated variety of a wild species. I took for my experiment the rough hawksbeard. In the summer of 1895 I isolated some atavists of the fifth generation of my race, which, by ordinary selection, gave in the average from 20-40% of fasciated stems. My isolated atavists bore abundant fruit, and from these I had the next year a set of some 350 plants, out of which about 20% had broadened and linear rosettes. This proportion corresponds with the degree of inheritance which is shown in many years by the largest and strongest [413] fasciated stems. It strengthens our conclusion as to the innermost constitution of the double races or ever-sporting varieties.

Twisted stems and fasciations are very striking monstrosities. But they are not very good for further investigation. They require too much space and too much care. The calculation of a single percentage requires the counting of some hundreds of individuals, taking many square meters for their cultivation, and this, as my best races are biennial, during two years. For this reason the countings must always be very limited, and selection is restrained to the most perfect specimens.

Now the question arises, whether this mark is the best upon which to found selection. This seems to be quite doubtful. In the experiments on the heredity of the atavists, we have seen that they are, at least often, in no manner inferior to even the best inheritors of the race. This suggests the idea that it is not at all certain that the visible characters of a given individual are a trustworthy measure of its value as to the transmission of the same character to the offspring. In other words, we are confronted with the existence of two widely different groups of characters in estimating the hereditary tendency. One is the visible quality of the individuals and the other is the direct observation [414] of the degree in which the attribute is transmitted. These are by no means parallel, and seem in some sense to be nearly independent of each other. The fact that the worst atavists may have the highest percentage of varietal units seems to leave no room for another explanation.

Developing this line of thought, we gradually arrive at the conclusion that the visible attribute of a varying individual is perhaps the most untrustworthy and the most unreliable character for selection, even if it seems in many cases practically to be the only available one. The direct determination of the degree of heredity itself is obviously preferable by far. This degree is expressed by the proportion of its inheritors among the offspring, and this figure therefore should be elevated to the highest rank, as a measure of the hereditary qualities. Henceforward we will designate it by the name of hereditary percentage.

In scientific experiments this figure must be determined for every plant of a pedigree-culture singly, and the selection should be founded exclusively or at least mainly on it. It is easily seen that this method requires large numbers of individuals to be grown and counted. Some two or three hundred progeny of one plant are needed to give the decisive figure for this one [415] individual, and selection requires the comparison of at least fifty or more individuals. This brings the total amount of specimens to be counted up to some tens of thousands. In practice, where important interests depend upon the experiments, such numbers are usually employed and often exceeded, but for the culture of monstrosities, other methods are to be sought in order to avoid these difficulties.