have the appearance, at first, of a move into a region of mystery and uncertainty. The lapse of time and the growth of familiarity with it are necessary to the reclamation of a terra incognita.

Before leaving this branch of my subject, I desire to call your attention to the very interesting fact that Mr. Darwin himself once conducted a long series of experiments which, it can hardly be doubted, resulted in the production of mutants and that he just missed the discovery of principles which are now the basis of scientific pedigree cultures and are occupying the attention of investigators of the problems of variation and heredity. In a letter to J. H. Gilbert, dated February 16, 1876, Mr. Darwin writes:

Now, for the last ten years I have been experimenting in crossing and self-fertilizing plants; and one indirect result has surprised me much, namely, that by taking pains to cultivate plants in pots under glass during several successive generations, under nearly similar conditions, and by self-fertilizing them in each generation, the colour of the flowers often changes, and, what is very remarkable, they became in some of the most variable species, such as Mimulus, Carnation, &c., quite constant, like those of a wild species. This fact and several others have led me to the suspicion that the cause of variation must be in different substances absorbed from the soil by these plants when their powers of absorption are not interfered with by other plants with which they grow mingled in a state of nature."2

The point I particularly wish you to notice in this case is that Mr. Darwin was employing practically the methods now used by Professor De Vries, Professor MacDougal and others who are engaged in species testing, by growing naturally variable or mutating plants under conditions of rigid control, so as to exclude crossing or, as De Vries calls it, vicinism. In this view of the matter, it would be interesting to know what percentage of Mr. Darwin's plants exhibited the new and constant characters and through how many generations his mutants were found to breed true, for then we could compare his results with those of investigators of our day. But his attention was centered upon the endeavor to find a cause 52Life and Letters," 1886, Vol. III, p. 343.

for the abrupt variations and not on the formulation of laws of their action. Apparently he considered isolation to be the principal secondary cause or favoring condition, upon which view the obvious comment is that it requires no great stretch of imagination to conceive of similar isolation as occurring in nature and thus favoring mutation among uncultivated forms.

Having now hastily reviewed the oscillations in Darwin's opinions concerning the kinds, the causes and the laws of variation with relation to the origin of species, it is not my purpose to enter upon a discussion of the presentday mutation theory, which has grown out of a closer study, and a more scientific treatment, of the problems of variation and heredity than were attempted, or were perhaps possible in Darwin's time. It is desirable, however, to compare Darwin's views with generalizations from the mutation theory, which we can do, well enough for our present purpose, by merely recalling the seven laws which De Vries claims to be the logical outcome of his twenty years of cultural experiments upon plants. They are, with slight modifications as to wording and order, as follows:

1. New elementary species appear suddenly without intermediate steps.

2. New forms spring laterally from the main stem. 3. New elementary species attain their full constancy

at once.

4. Some of the new strains are elementary species, while others are to be considered as retrograde varieties. 5. The same new species are produced in a large number of individuals.

6. Mutations take place in nearly all directions and are due to unknown causes.

7. Species and varieties have originated by mutation, but are, at present, not known to have originated in any

other way.

Now, looking back over what Darwin wrote concerning variation, I can not believe that he would seriously have

He

disputed any of De Vries's propositions except the last. All would have had to stand or fall with that. recognized the fact that new species had sometimes appeared suddenly without intermediate steps and that the new forms had sprung laterally from the main stem. I think he also substantially admitted that such new species attained their full constancy at once. As to the fourth affirmation of De Vries, with reference to elementary species and retrograde varieties, Darwin had no knowledge, for the distinction is original with De Vries. Darwin believed, as a general proposition, that "species are only strongly marked and permanent varieties, and that each species first existed as a variety, '53 but, of course, in admitted cases of mutation this can not be true; and if Darwin had been obliged to concede De Vries's seventh proposition, the fourth might well have been allowed to go with it. The same is doubtless the case concerning De Vries's fifth law, which sets forth in effect that similar mutants are thrown off by many individuals of the same species at about the same time. As we have already seen, Mr. Darwin was convinced that if, for example, he were to admit the origin by mutation of a species of flying animal, for the reasons urged by Mr. Mivart, he would be compelled to assume that many individuals varied simultaneously." I, therefore, do not see that he would have been interested, from a theoretical point of view, in disputing either of the two last-named declarations of De Vries except in connection with his seventh and last law, to which I shall presently refer. The sixth law of De Vries, which affirms that mutations take place in nearly all directions, is practically the equivalent of Darwin's first law that all organisms vary continually and in every part of their structure, provided it is agreed that mutations are only quantitatively different from Darwin's "individual variations," which was Darwin's own view. In so far as Darwin admitted the occurrence of mutation at all, he must have agreed that it could proceed in any 53Origin of Species," 6th ed., 1882, p. 412.

direction. But now we come to the conclusion of De Vries which we know Darwin would not have accepted, at least in its entirety. As we have seen, he was compelled to concede that what we now call mutation had occasionally taken place and become the starting point of new races, but he was none the less unshaken in the conviction that this process was exceptional and extraordinary, and that, as a rule, a new species originated by the gradual building up of minute and even insignificant deviations from the average characters of an old species, which deviations we now call fluctuations. We know with what tenacity he held this view to the end of his life. For the doctrine of "insensible gradations, which touched mainly a minor premise in his general argument for evolution, Mr. Darwin was, unhappily, almost willing to relinquish the essence of the whole matter, which was his claim to the discovery of a vera in the evolutionary process. Notwithstanding the prior claim of Patrick Matthew, and the partial anticipation of Alfred R. Wallace and others, the establishment of the theory of natural selection was Mr. Darwin's most original and greatest achievement. Time has proved that he could have afforded to stand upon the general validity and applicability of this theory though every step in his argument in its favor had needed review and modification; for each passing year but adds to the impregnable mass of proofs by which it is affirmed and supported. Properly regarded, the mutation theory does not antagonize nor weaken the doctrine of natural selection-on the contrary, it merely offers itself as a helpful substitute

causa

for, or

adjunct to, one of Darwin's subordinate steps in

the approach to a consistent philosophy of the origin of species, leaving the last great cause of evolution as

efficient as ever.

It is, therefore, one of the tragedies of

science that in this matter Darwin should have been ready to surrender his main position rather than to receive and to join forces with those who were coming to his aid, but whom he failed to recognize as friends.

JUVENILE KELPS AND THE RECAPITULATION

THEORY. II

PROFESSOR ROBERT F. GREGGS

OHIO STATE UNIVERSITY

II. THE RECAPITULATION THEORY IN RELATION TO THE KELPS

ANY observations on juvenile kelps must call to mind the recapitulation theory. This theory, though applied both to animals and to plants, was built up exclusively on zoological evidence and has been amplified and discussed chiefly by zoologists. The reason is evident because of the definite proportions and structure of the animal body, the development of which must of necessity follow a very definite course, while among plants the body is of such loose and indefinite proportions that its development can seldom be rigidly described. But while the botanists have had very little to say about the recapitulation theory, they have always approved it and considered that it applied to plants just as truly, though not as conspicuously, as to animals.

It is somewhat surprising then to a botanist to find that this theory is being very vigorously attacked by some of the zoologists. One of the more recent papers is by Montgomery, who gives a review of the literature with a general discussion of the theory in his "Analysis of Racial Descent," 1906. In summing up he says (p. 193):

Therefore we can only conclude that the embryogeny does not furnish any recapitulation of the phylogeny, not even a recapitulation marred at occasional points by secondary change. . . . An analysis of the stages during the life of one individual can in no way present a knowledge of its ancestry; and the method of comparing non-correspondent stages of two species is entirely wrong in principle.

And again at the close of the chapter, p. 203:

The recapitulation hypothesis is scientifically untenable and where there has been transmutation of species, the embryogeny neither in