492 



SCIENCE 



[N. S. Vol. XXXIV. No. 876 



The publication of volume two wUl help to 

 dispel the erroneous, but still quite prevalent, 

 notion that the theory of mutation is based 

 entirely on observations of the evening-prim- 

 rose. Even one who has himself carried on 

 experimental pedigreed cultures can not but 

 admire the thoroughness and patience with 

 which thousands of individual plants of scores 

 of different species were examined with 

 minutest care in order to insure adequate 

 grounds for inductive inference, or to secure 

 sufficient data for the confirmation or rejec- 

 tion of a hypothesis. The conception and 

 elaboration of this hypothesis of mutation is 

 the most Darwin-like performance since Dar- 

 win, and is, without doubt, one of the most 

 important fruits of Darwin's labors. Like the 

 source of its inspiration (the " Origin of 

 Species"), "Die Mutationstheorie " has given 

 color and direction to all lines of biological 

 inquiry, which will persist for decades to 

 come. 



As in volume one, so also throughout vol- 

 ume two, the author keeps close to Darwin's 

 Darwinism, and insists that, far from being 

 intended to supplant the theory of selection, 

 as Darwin held it, the mutation theory is in- 

 tended merely to complement the other. Thus 

 on page 609 : " To Darwin's mind the essential 

 point was . . . that natural selection is a sieve. 

 ... It creates nothing, as is so often assumed; 

 it only sifts. . . . How the struggle for exist- 

 ence sifts is one question; how that which is 

 sifted arose is another." It is really difficult 

 to conceive how careful readers could ever 

 have confused the issue on this point. Any 

 attempt to restate in this periodical the es- 

 sence of the mutation-theory would now be out 

 of place. 



That phase of de Vries's philosophy which 

 has perhaps met with the greatest opposition 

 is his hypothesis of intracellular pangenesis. 

 It has been rejected as too mechanical and too 

 formal, one author implying that pangens are 

 more " mechanical" than atoms and molecules ! 

 This is not the place to discuss the validity of 

 intracellular pangenesis, but it must surely be 

 recognized that as a working hypothesis it has 

 fully justified itself, since it lies at the bot- 



tom of all of de Vries's experiments, and of 

 his own explanation of the results. Putting 

 aside the question of its heuristic value, its 

 framer says (p. 643) : " for myself pangenesis 

 has always been the starting point of my 

 inquiries; at first only in a theoretical way, 

 but afterwards also for the experimental in- 

 vestigations described in this book. Espe- 

 ■ cially is it this hypothesis which has led me to 

 search for mutations in the field." It is doubt- 

 ful whether the field observations which led to 

 the classical experiments with Lamarck's even- 

 ing-primrose and thus to the actual observa- 

 tion of the origin of elementary species, would 

 ever have been made if the hypothesis of 

 intracellular pangenesis had not first taken 

 form in our author's thought (see footnote 3, 

 p. 643, and " Intracellular Pangenesis," Eng- 

 lish edition, p. 74, footnote). 



Whether we accept intracellular pangenesis 

 as an expression of truth or not, and even if 

 we reject it as a working hypothesis, a clear 

 understanding of it is absolutely essential in 

 order to interpret the theory of mutation as it 

 exists in the mind of de Vries. It was largely 

 for this reason that the present writer thought 

 it worth while to translate " Intracellular 

 Pangenesis " into English. 



In the language of intracellular pangenesis : 



1. Premutation consists in the formation of 

 a new pangen. 



2. Progressive mutation consists in premu- 

 tation, plus the initial activation of the new 

 pangen. The result is a new elementary 

 species. 



3. Retrogressive mutation is the reverse of 

 progressive mutation; it consists in the re- 

 turn of a pangen from an active to a latent 

 condition. White-flowered varieties are thus 

 caused. 



4. Degressive mutation consists in such a 

 transposition of pangens that either (a) the 

 more recently activated pangens become semi- 

 latent, being active in rare instances only, 

 thus giving rise to a half-race (e. g., wild four- 

 leaved clovers, and other teratological forms) ; 

 or (b) the active pangens become semi-active, 

 giving rise to ever-sporting varieties, middle 

 races (e. g., Trifolium ■^atense quinquefolium 



