Lecture Xix

EXPERIMENTAL PEDIGREE-CULTURES

The observation of the production of mutants in the field at Hilversum, and the subsequent cultivation of the new types in the garden at Amsterdam, gives ample proof of the mutability of plants. Furthermore it furnishes an analogy with the hypothetical origin of the swarms of species of Draba and Viola. Last but not least important it affords material for a complete systematic and morphologic study of the newly arisen group of forms.

The physiologic laws, however, which govern this process are only very imperfectly revealed by such a study. The instances are too few. Moreover the seeds from which the mutants spring, escape observation. It is simply impossible to tell from which individual plants they have been derived. The laevifolia and the brevistylis have been found almost every year, the first always recurring on the same spot, the second on various parts of the original field. It is therefore allowable to assume a common origin for all the observed individuals of either strain. But whether, besides this, similar strains are produced anew by the old lamarckiana group, it is impossible to decide on the sole ground of these field-observations.

The same holds good with the other novelties. Even if one of them should germinate repeatedly, without ever opening its flowers, the possibility could not be excluded that the seeds might have come originally from the same capsule but lain dormant in the earth during periods of unequal length.

Other objections might be cited that can only be met by direct and fully controlled experiments. Next to the native locality comes the experimental garden. Here the rule prevails that every plant must be fertilized with pollen of its own, or with pollen of other individuals of known and recorded origin. The visits of insects must be guarded against, and no seeds should be saved from flowers which have been allowed to open without this precaution. Then the seeds of each individual must be saved and sown separately, so as to admit of an appreciation, and if necessary, a numerical determination of the nature of its progeny. And last but not least the experiments should be conducted in a similar manner during a series of successive years.

I have made four such experiments, each comprising the handling of many thousands of individual plants, and lasting through five to nine generations. At the beginning the plants were biennial, as in the native locality, but later I learned to cultivate them in annual generations. They have been started from different plants and seeds, introduced from the original field into my garden at Amsterdam.

It seems sufficient to describe here one of these pedigree-cultures, as the results of all four were similar. In the fall of 1886 I took nine large rosettes from the field, planted them together on an isolated spot in the garden, and harvested their seeds the next year. These nine original plants are therefore to be considered as constituting the first generation of my race. The second generation was sown in 1888 and flowered in 1889. It at once yielded the expected result. 15,000 seedlings were tested and examined, and among them 10 showed diverging characters. They were properly protected, and proved to belong to two new types. 5 of them were lata and 5 nanella. They flowered next year and displayed all the characters as described in our preceding lecture. Intermediates between them and the general type were not found, and no indication of their appearance was noted in their parents. They came into existence at once, fully equipped, without preparation or intermediate steps. No series of generations, no selection, no struggle for existence was needed. It was a sudden leap into another type, a sport in the best acceptation of the word. It fulfilled my hopes, and at once gave proof of the possibility of the direct observation of the origin of species, and of the experimental control thereof.

The third generation was in the main a repetition of the second. I tried some 10,000 seedlings and found three lata and three nanella, or nearly the same proportion as in the first instance. But besides these a rubrinervis made its appearance and flowered the following year. This fact at once revealed the possibility that the instability of lamarckiana might not be restricted to the three new types now under observation. Hence the question arose how it would be possible to obtain other types or to find them if they were present. It was necessary to have better methods of cultivation and examination of the young plants. Accordingly I devoted the three succeeding years to working on this problem.

I found that it was not at all necessary to sow any larger quantities of seed, but that the young plants must have room enough to develop into full and free rosettes. Moreover I observed that the attributes of lata and nanella, which I now studied in the offspring of my first mutants, were clearly discernible in extreme youth, while those of rubrinervis remained concealed some weeks longer. Hence I concluded that the young plants should be examined from time to time until they proved clearly to be only normal lamarckiana. Individuals exhibiting any deviation from the type, or even giving only a slight indication of it, were forthwith taken out of the beds and planted separately, under circumstances as favorable as possible. They were established in pots with well-manured soil and kept under glass, but fully exposed to sunshine. As a rule they grew very fast, and could be planted out early in June. Some of them, of course, proved to have been erroneously taken for mutants, but many exhibited new characters.

All in all I had 334 young plants which did not agree with the parental type. As I examined some 14,000 seedlings altogether, the result was estimated at about 2.5%. This proportion is much larger than in the yields of the two first generations and illustrates the value of improved methods. No doubt many good mutations had been overlooked in the earlier observations.

As was to be expected, lata and nanella were repeated in this third generation (1895). I was sure to get nearly all of them, without any important exceptions, as I now knew how to detect them at almost any age. In fact, I found many of them; as many as 60 nanella and 73 lata, or nearly 5% of each. Rubrinervis also recurred, and was seen in 8 specimens. It was much more rare than the two first-named types.

But the most curious fact in that year was the appearance of oblonga. No doubt I had often seen it in former years, but had not attached any value to the very slight differences from the type, as they then seemed to me. I knew now that any divergence was to be esteemed as important, and should be isolated for further observation. This showed that among the selected specimens not less than 176, or more than 1% belonged to the oblonga type. This type was at that time quite new to me, and it had to be kept through the winter, to obtain stems and flowers. It proved to be as uniform as its three predecessors, and especially as sharply contrasted with lamarckiana. The opportunity for the discovery of any intermediates was as favorable as could be, because the distinguishing marks were hardly beyond doubt at the time of the selection and removal of the young plants. But no connecting links were found.

The same holds good for albida, which appeared in 15 specimens, or in 0.1%, of the whole culture. By careful cultivation these plants proved not to be sickly, but to belong to a new, though weak type. It was evident that I had already seen them in former years, but having failed to recognize them had allowed them to be destroyed at an early age, not knowing how to protect them against adverse circumstances. Even this time I did not succeed in getting them strong enough to keep through the winter.

Besides these, two new types were observed, completing the range of all that have since been recorded to regularly occur in this family. They were scintillans and gigas. The first was obtained in the way just described. The other hardly escaped being destroyed, not having showed itself early enough, and being left in the bed after the end of the selection. But as it was necessary to keep some rosettes through the winter in order to have biennial flowering plants to furnish seeds, I selected in August about 30 of the most vigorous plants, planted them on another bed and gave them sufficient room for their stems and branches in the following summer. Most of them sent up robust shoots, but no difference was noted till the first flowers opened. One plant had a much larger crown of bright blossoms than any of the others. As soon as these flowers faded away, and the young fruits grew out, it became clear that a new type was showing itself. On that indication I removed all the already fertilized flowers and young fruits, and protected the buds from the visits of insects. Thus the isolated flowers were fertilized with their own pollen only, and I could rely upon the purity of the seed saved. This lot of seeds was sown in the spring of 1897 and yielded a uniform crop of nearly 300 young gigas plants.

Having found how much depends upon the treatment, I could gradually decrease the size of my cultures. Evidently the chance of discovering new types would be lessened thereby, but the question as to the repeated production of the same new forms could more easily and more clearly be answered in this way. In the following year (1896) I sowed half as many seeds as formerly, and the result proved quite the same. With the exception of gigas all the described forms sprang anew from the purely fertilized ancestry of normal lamarckianas. It was now the fifth generation of my pedigree, and thus I was absolutely sure that the descendants of the mutants of this year had been pure and without deviation for at least four successive generations.

Owing partly to improved methods of selection, partly no doubt to chance, even more mutants were found this year than in the former. Out of some 8,000 seedlings I counted 377 deviating ones, or nearly 5%, which is a high proportion. Most of them were oblonga and lata, the same types that had constituted the majority in the former year.

Albida, nanella and rubrinervis appeared in large numbers, and even scintillans, of which I had but a single plant in the previous generation, was repeated sixfold.

New forms did not arise, and the capacity of my strain seemed exhausted. This conclusion was strengthened by the results of the next three generations, which were made on a much smaller scale and yielded the same, or at least the mutants most commonly seen in previous years.

Instead of giving the figures for these last two years separately, I will now summarize my whole experiment in the form of a pedigree. In this the normal lamarckiana was the main line, and seeds were only sown from plants after sufficient isolation either of the plants themselves, or in the latter years by means of paper bags enclosing the inflorescences. I have given the number of seedlings of lamarckiana which were examined each year in the table below. Of course by far the largest number of them were thrown away as soon as they showed their differentiating characters in order to make room for the remaining ones. At last only a few plants were left to blossom in order to perpetuate the race. I have indicated for each generation the number of mutants of each of the observed forms, placing them in vertical columns underneath their respective heads. The three first generations were biennial, but the five last annual.

PEDIGREE OF A MUTATING FAMILY OF OENOTHERA LAMARCKIANA IN THE EXPERIMENTAL GARDEN AT AMSTERDAM

Gener: O.gig. albida obl. rubrin. Lam. nanella lata. scint. VIII. 5 1 0 1700 21 1 VII. 9 0 3000 11 VI. 11 29 3 1800 9 5 1 V. 25 135 20 8000 49 142 6 IV. 1 15 176 8 14000 60 73 1 III. 1 10000 3 3 II. 15000 5 5 I. 9

It is most striking that the various mutations of the evening-primrose display a great degree of regularity. There is no chaos of forms, no indefinite varying in all degrees and in all directions. Quite on the contrary, it is at once evident that very simple rules govern the whole phenomenon.

I shall now attempt to deduce these laws from my experiment. Obviously they apply not only to our evening-primroses, but may be expected to be of general validity. This is at once manifest, if we compare the group of new mutants with the swarms of elementary forms which compose some of the youngest systematic species, and which, as we have seen before, are to be considered as the results of previous mutations. The difference lies in the fact that the evening-primroses have been seen to spring from their ancestors and that the drabas have not. Hence the conclusion that in comparing the two we must leave out the pedigree of the evening-primroses and consider only the group of forms as they finally show themselves. If in doing so we find sufficient similarity, we are justified in the conclusion that the drabas and others have probably originated in the same way as the evening-primroses. Minor points of course will differ, but the main lines cannot have complied with wholly different laws. All so-called swarms of elementary species obviously pertain to a single type, and this type includes our evening-primroses as the only controlled case.

Formulating the laws of mutability for the evening-primroses we therefore assume that they hold good for numerous other corresponding cases.

I. The first law is, that new elementary species appear suddenly, without intermediate steps.

This is a striking point, and the one that is in the most immediate contradiction to current scientific belief. The ordinary conception assumes very slow changes, in fact so slow that centuries are supposed to be required to make the differences appreciable. If this were true, all chance of ever seeing a new species arise would be hopelessly small. Fortunately the evening-primroses exhibit contrary tendencies. One of the great points of pedigree-culture is the fact that the ancestors of every mutant have been controlled and recorded. Those of the last year have seven generations of known lamarckiana parents preceding them. If there had been any visible preparation towards the coming mutation, it could not have escaped observation. Moreover, if visible preparation were the rule, it could hardly go on at the same time and in the same individuals in five or six diverging directions, producing from one parent, gigas and nanella, lata and rubrinervis, oblonga and albida and even scintillans.

On the other hand the mutants, that constitute the first representatives of their race, exhibit all the attributes of the new type in full display at once. No series of generations, no selection, no struggle for existence are needed to reach this end. In previous lectures I have mentioned that I have saved the seeds of the mutants whenever possible, and have always obtained repetitions of the prototype only. Reversions are as absolutely lacking as is also a further development of the new type. Even in the case of the inconstant forms, where part of the progeny yearly return to the stature of lamarckiana, intermediates are not found. So it is also with lata, which is pistillate and can only be propagated by cross-fertilization. But though the current belief would expect intermediates at least in this case, they do not occur. I made a pedigree-culture of lata during eight successive generations, pollinating them in different ways, and always obtained cultures which were partly constituted of lata and partly of lamarckiana specimens. But the latas remained lata in all the various and most noticeable characters, never showing any tendency to gradually revert into the original form.

Intermediate forms, if not occurring in the direct line from one species to another, might be expected to appear perhaps on lateral branches. In this case the mutants of one type, appearing in the same year, would not be a pure type, but would exhibit different degrees of deviation from the parent. The best would then have to be chosen in order to get the new type in its pure condition. Nothing of the kind, however, was observed. All the oblonga-mutants were pure oblongas. The pedigree shows hundreds of them in the succeeding years, but no difference was seen and no material for selection was afforded. All were as nearly equal as the individuals of old elementary species.

II. New forms spring laterally from the main stem.

The current conception concerning the origin of species assumes that species are slowly converted into others. The conversion is assumed to affect all the individuals in the same direction and in the same degree. The whole group changes its character, acquiring new attributes. By inter-crossing they maintain a common line of progress, one individual never being able to proceed much ahead of the others.

The birth of the new species necessarily seemed to involve the death of the old one. This last conclusion, however, is hard to understand. It may be justifiable to assume that all the individuals of one locality are ordinarily intercrossed, and are moreover subjected to the same external conditions. They might be supposed to vary in the same direction if these conditions were changed slowly. But this could of course have no possible influence on the plants of the same species growing in distant localities, and it would be improbable they should be affected in the same way. Hence we should conclude that when a species is converted into a new type in one locality this is only to be considered as one of numerous possible ones, and its alteration would not in the least change the aspect of the remainder of the species.

But even with this restriction the general belief is not supported by the evidence of the evening-primroses. There is neither a slow nor a sudden change of all the individuals. On the contrary, the vast majority remain unchanged; thousands are seen exactly repeating the original prototype yearly, both in the native field and in my garden. There is no danger that lamarckiana might die out from the act of mutating, nor that the mutating strain itself would be exposed to ultimate destruction from this cause.

In older swarms, such as Draba or Helianthemum, no such center, around which the various forms are grouped, is known. Are we to conclude therefore that the main strain has died out? Or is it perhaps concealed among the throng, being distinguished by no peculiar character? If our gigas and rubrinervis were growing in equal numbers with the lamarckiana in the native field, would it be possible to decide which of them was the progenitor of the others? Of course this could be done by long and tedious crossing experiments, showing atavism in the progeny, and thereby indicating the common ancestor. But even this capacity seems to be doubtful and connected only with the state of mutability and to be lost afterwards. Therefore if this period of mutation were ended, probably there would be no way to decide concerning the mutual relationship of the single species.

Hence the lack of a recognizable main stem in swarms of elementary species makes it impossible to answer the question concerning their common origin.

Another phase of the opposition between the prevailing view and my own results seems far more important. According to the current belief the conversion of a group of plants growing in any locality and flowering simultaneously would be restricted to one type. In my own experiments several new species arose from the parental form at once, giving a wide range of new forms at the same time and under the same conditions.

III. New elementary species attain their full constancy at once.

Constancy is not the result of selection or of improvement. It is a quality of its own. It can neither be constrained by selection if it is absent from the beginning, nor does it need any natural or artificial aid if it is present. Most of my new species have proved constant from the first. Whenever possible, the original mutants have been isolated during the flowering period and artificially self-fertilized. Such plants have always given a uniform progeny, all children exhibiting the type of the parent. No atavism was observed and therefore no selection was needed or even practicable.

Briefly considering the different forms, we may state that the full experimental proof has been given for the origin of gigas and rubrinervis, for albida and oblonga, and even for nanella, which is to be considered as of a varietal nature; with lata the decisive experiment is excluded by its unisexuality. laevifolia and brevistylis were found originally in the field, and never appeared in my cultures. No observations were made as to their origin, and seeds have only been sown from later generations. But these have yielded uniform crops, thereby showing that there is no ground for the assumption that these two older varieties might behave otherwise than the more recent derivatives.

Scintillans and elliptica constitute exceptions to the rule given. They repeat their character, from pure seed, only in part of the offspring. I have tried to deliver the scintillans from this incompleteness of heredity, but in vain. The succeeding generations, if produced from true representatives of the new type, and with pure fertilization, have repeated the splitting in the same numerical proportions. The instability seems to be here as permanent a quality as the stability in other instances. Even here no selection has been adequate to change the original form.

IV. Some of the new strains are evidently elementary species, while others are to be considered as retrograde varieties.

It is often difficult to decide whether a given form belongs to one or another of these two groups. I have tried to show that the best and strictest conception of varieties limits them to those forms that have probably originated by retrograde or degressive steps. Elementary species are assumed to have been produced in a progressive way, adding one new element to the store. Varieties differ from their species clearly in one point, and this is either a distinct loss, or the assumption of a character, which may be met with in other species and genera. laevifolia is distinguished by the loss of the crinkling of the leaves, brevistylis by the partial loss of the epigynous qualities of the flowers, and nanella is a dwarf. These three new forms are therefore considered to constitute only retrograde steps, and no advance. This conclusion has been fully justified by some crossing experiments with brevistylis, which wholly complies with Mendel's law, and in one instance with nanella, which behaves in the same manner, if crossed with rubrinervis.

On the other hand, gigas and rubrinervis, oblonga and albida obviously bear the characters of progressive elementary species. They are not differentiated from lamarckiana by one or two main features. They diverge from it in nearly all organs, and in all in a definite though small degree. They may be recognized as soon as they have developed their first leaves and remain discernible throughout life. Their characters refer chiefly to the foliage, but no less to the stature, and even the seeds have peculiarities. There can be little doubt but that all the attributes of every new species are derived from one principal change. But why this should affect the foliage in one manner, the flowers in another and the fruits in a third direction, remains obscure. To gain ever so little an insight into the nature of these changes, we may best compare the differences of our evening-primroses with those between the two hundred elementary species of Draba and other similar instances. In doing so we find the same main feature, the minute differences in nearly all points.

V. The same new species are produced in a large number of individuals.

This is a very curious fact. It embraces two minor points, viz: the multitude of similar mutants in the same year, and the repetition thereof in succeeding generations. Obviously there must be some common cause. This cause must be assumed to lie dormant in the Lamarckianas of my strain, and probably in all of them, as no single parent-plant proved ever to be wholly destitute of mutability. Furthermore the different causes for the sundry mutations must lie latent together in the same parent-plant. They obey the same general laws, become active under similar conditions, some of them being more easily awakened than others. The germs of the oblonga, lata and nanella are especially irritable, and are ready to spring into activity at the least summons, while those of gigas, rubrinervis and scintillans are far more difficult to arouse.

These germs must be assumed to lie dormant during many successive generations. This is especially evident in the case of lata and nanella, which appeared in the first year of the pedigree culture and which since have been repeated yearly, and have been seen to arise by mutation also during the last season (1903). Only gigas_ appeared but once, but then there is every reason to assume that in larger sowings or by a prolongation of the experiments it might have made a second appearance.

Is the number of such germs to be supposed to be limited or unlimited? My experiment has produced about a dozen new forms. Without doubt I could easily have succeeded in getting more, if I had had any definite reason to search for them. But such figures are far from favoring the assumption of indefinite mutability. The group of possible new forms is no doubt sharply circumscribed. Partly so by the morphologic peculiarities of lamarckiana, which seem to exclude red flowers, composite leaves, etc. No doubt there are more direct reasons for these limits, some changes having taken place initially and others later, while the present mutations are only repetitions of previous ones, and do not contribute new lines of development to those already existing. This leads us to the supposition of some common original cause, which produced a number of changes, but which itself is no longer at work, but has left the affected qualities, and only these, in the state of mutability.

In nature, repeated mutations must be of far greater significance than isolated ones. How great is the chance for a single individual to be destroyed in the struggle for life? Hundreds of thousands of seeds are produced by lamarckiana annually in the field, and only some slow increase of the number of specimens can be observed. Many seeds do not find the proper circumstances for germination, or the young seedlings are destroyed by lack of water, of air, or of space. Thousands of them are so crowded when becoming rosettes that only a few succeed in producing stems. Any weakness would have destroyed them. As a matter of fact they are much oftener produced in the seed than seen in the field with the usual unfavorable conditions; the careful sowing of collected seeds has given proof of this fact many times.

The experimental proof of this frequency in the origin of new types, seems to overcome many difficulties offered by the current theories on the probable origin of species at large.

VI. The relation between mutability and fluctuating variability has always been one of the chief difficulties of the followers of Darwin. The majority assumed that species arise by the slow accumulation of slight fluctuating deviations, and the mutations were only to be considered as extreme fluctuations, obtained, in the main, by a continuous selection of small differences in a constant direction.

My cultures show that quite the opposite is to be regarded as fact. All organs and all qualities of lamarckiana fluctuate and vary in a more or less evident manner, and those which I had the opportunity of examining more closely were found to comply with the general laws of fluctuation. But such oscillating changes have nothing in common with the mutations. Their essential character is the heaping up of slight deviations around a mean, and the occurrence of continuous lines of increasing deviations, linking the extremes with this group. Nothing of the kind is observed in the case of mutations. There is no mean for them to be grouped around and the extreme only is to be seen, and it is wholly unconnected with the original type. It might be supposed that on closer inspection each mutation might be brought into connection with some feature of the fluctuating variability. But this is not the case. The dwarfs are not at all the extreme variants of structure, as the fluctuation of the height of the lamarckiana never decreases or even approaches that of the dwarfs. There is always a gap. The smallest specimens of the tall type are commonly the weakest, according to the general rule of the relationship between nourishment and variation, but the tallest dwarfs are of course the most robust specimens of their group. Fluctuating variability, as a rule, is subject to reversion. The seeds of the extremes do not produce an offspring which fluctuates around their parents as a center, but around some point on the line which combines their attributes with the corresponding characteristic of their ancestors, as Vilmorin has put it. No reversion accompanies mutation, and this fact is perhaps the completest contrast in which these two great types of variability are opposed to each other.

The offspring of my mutants are, of course, subject to the general laws of fluctuating variability. They vary, however, around their own mean, and this mean is simply the type of the new elementary species.

VII. The mutations take place in nearly all directions.

Many authors assume that the origin of species is directed by unknown causes. These causes are assumed to work in each single case for the improvement of the animals and plants, changing them in a manner corresponding in a useful way to the changes that take place in their environment. It is not easy to imagine the nature of these influences nor how they would bring about the desired effect.

This difficulty was strongly felt by Darwin, and one of the chief purposes of his selection theory may be said to have been the attempt to surmount it. Darwin tried to replace the unknown cause by natural agencies, which lie under our immediate observation. On this point Darwin was superior to his predecessors, and it is chiefly due to the clear conception of this point that his theory has gained its deserved general acceptance. According to Darwin, changes occur in all directions, quite independently of the prevailing circumstances. Some may be favorable, others detrimental, many of them without significance, neither useful nor injurious. Some of them will sooner or later be destroyed, while others will survive, but which of them will survive, is obviously dependent upon whether their particular changes agree with the existing environic conditions or not. This is what Darwin has called the struggle for life. It is a large sieve, and it only acts as such. Some fall through and are annihilated, others remain above and are selected, as the phrase goes. Many are selected, but more are destroyed; daily observation does not leave any doubt upon this point.

How the differences originate is quite another question. It has nothing to do with the theory of natural selection nor with the struggle for life. These have an active part only in the accumulation of useful qualities, and only in so far as they protect the bearers of such characters against being crowded out by their more poorly constituted competitors.

However, the differentiating characteristics of elementary species are only very small. How widely distant they are from the beautiful adaptative organizations of orchids, of insectivorous plants and of so many others! Here the difference lies in the accumulation of numerous elementary characters, which all contribute to the same end. Chance must have produced them, and this would seem absolutely improbable, even impossible, were it not for Darwin's ingenious theory. Chance there is, but no more than anywhere else. It is not by mere chance that the variations move in the required direction. They do go, according to Darwin's view, in all directions, or at least in many. If these include the useful ones, and if this is repeated a number of times, cumulation is possible; if not, there is simply no progression, and the type remains stable through the ages. Natural selection is continually acting as a sieve, throwing out the useless changes and retaining the real improvements. Hence the accumulation in apparently predisposed directions, and hence the increasing adaptations to the more specialized conditions of life. It must be obvious to any one who can free himself from the current ideas, that this theory of natural selection leaves the question as to how the changes themselves are brought about, quite undecided. There are two possibilities, and both have been propounded by Darwin. One is the accumulation of the slight deviations of fluctuating variability, the other consists of successive sports or leaps taking place in the same direction.

In further lectures a critical comparison of the two views will be given. Today I have only to show that the mutations of the evening-primroses, though sudden, comply with the demands made by Darwin as to the form of variability which is to be accepted as the cause of evolution and as the origin of species.

Some of my new types are stouter and others weaker than their parents, as shown by gigas and albida. Some have broader leaves and some narrower, lata and oblonga. Some have larger flowers (gigas) or deeper yellow ones (rubrinervis), or smaller blossoms (scintillans), or of a paler hue (albida). In some the capsules are longer (rubrinervis), or thicker (gigas), or more rounded (lata), or small (oblonga), and nearly destitute of seeds (brevistylis). The unevenness of the surface of the leaves may increase as in lata, or decrease as in laevifolia. The tendency to become annual prevails in rubrinervis, but gigas tends to become biennial. Some are rich in pollen, while scintillans is poor. Some have large seeds, others small. Lata has become pistillate, while brevistylis has nearly lost the faculty to produce seeds. Some undescribed forms were quite sterile, and some I observed which produced no flowers at all. From this statement it may be seen that nearly all qualities vary in opposite directions and that our group of mutants affords wide material for the sifting process of natural selection. On the original field the laevifolia and brevistylis have held their own during sixteen years and probably more, without, however, being able to increase their numbers to any noticeable extent. Others perish as soon as they make their appearance, or a few individuals are allowed to bloom, but probably leave no progeny.

But perhaps the circumstances may change, or the whole strain may be dispersed and spread to new localities with different conditions. Some of the latter might be found to be favorable to the robust gigas, or to rubrinervis, which requires a drier air, with rainfall in the springtime and sunshine during the summer. It would be worth while to see whether the climate of California, where neither O. lamarckiana nor O. biennis are found wild, would not exactly suit the requirements of the new species rubrinervis and gigas.

NOTE. Oenotheras are native to America and all of the species growing in Europe have escaped from gardens directly, or may have arisen by mutation, or by hybridization of introduced species. A fixed hybrid between O. cruciata and O. biennis constituting a species has been in cultivation for many years. The form known as O. biennis in Europe, and used by de Vries in all of the experiments described in these lectures, has not yet been found growing wild in America and is not identical with the species bearing that name among American botanists. Concerning this matter Professor de Vries writes under date of Sept. 12, 1905: "The 'biennis' which I collected in America has proved to be a motley collection of forms, which at that time I had no means of distinguishing. No one of them, so far as they are now growing in my garden is identical with our biennis of the sand dunes." The same appears to be the case with O. muricata. Plants from the Northeastern American seaboard, identifiable with the species do not entirely agree with those raised from seed received from Holland.

O. lamarckiana has not been found growing wild in America in recent years although the evidence at hand seems to favor the conclusion that it was seen and collected in the southern states in the last century. (See MacDougal, Vail, Shull, and Small: Mutants and Hybrids of the Oenotheras. Publication 24. Carnegie Institution. Washington, D.C., 1905.) EDITOR.