74 



SCIENCE 



[N. S. Vol. LI. No. 1308 



continuity as against discontinuity in tlie 

 phenomena of variation, inheritance and evo- 

 lution." And with this verdict his reviewer 

 is not inclined to disagree, because as a care- 

 ful study of Whitman's evidence and mean- 

 ing shows, there is not much difference be- 

 tween what he understood by continuity and 

 what is to-day called more often discontinuity. 



In the introductory chapter from a manu- 

 script written in 1909 that formed part of a 

 lecture given at Clark University, the keynote 

 to Whitman's antagonism to the mutation 

 theory of de Vries is struck — a note that 

 recurs throughout the first two volumes. 

 Weismann, he says, taught us to look to 

 germinal variation as the source of all varia- 

 tion that is hereditary. Then follows a para- 

 graph that takes us to the heart of the matter : 

 " Do we not have, then, in germinal variation, 

 a better criterion of what is specific than we 

 get in sudden appearance? Indeed, is it not 

 here that the seeming suddenness of first ap- 

 pearance finds its explanation, and likewise the 

 fact that so-called mutations involve the whole 

 organism ? If we are to accept the physiolog- 

 ical conception of development, as is inevit- 

 able in my opinion, it is easy to see that a 

 change, however slight, in the primordial con- 

 stitution of the germ would tend to correlate 

 itself with every part of the whole germ-sys- 

 tem, so that the end stage of development 

 would present a new facies and appear as a 

 total modification, answering to what de Vries 

 would call a mutation. That some thing of 

 this order does sometimes occiu- I have in- 

 dubitable evidence, and in such form as to 

 dispel the idea of discontinuity and sudden 

 gaps in transformation." 



With a slight shift of wording and emphasis 

 the essential part of this statement is not very 

 different from what we think to-day, for who 

 will dispute now that a change (mutation) in 

 the germ-plasm may affect many parts of the 

 organism that develops out of such a changed 

 germ-plasm ? Such a view has not been found 

 to dispel the idea of " discontinuity " of 

 characters; on the contrary it is in full accord 

 with it. 



But the unit character is Whitman's ieie 

 noir. "The idea of unit-characters, however. 



as distinct elements that can be removed or 

 introduced bodily into the germ does not 

 appeal to me as removing difficulties, but 

 rather as hiding them; in short, as a return 

 to the old pangenesis view of preformed char- 

 acters. In this theory, as is well known, we 

 have two miracles involved. The first con- 

 sisted in a centripetal migration of preformed 

 gemmules, and the second in the centrifugal 

 distribution of the same elements. DeVries 

 dismisses the first of these, but accepts the 

 second, and on it rears the superstructure of 

 his theory of mutable-immutable unit-char- 

 acters. With all due respect to the distin- 

 guished author of this theory, and with 

 abounding admiration for his great work and 

 model methods, which have aroused universal 

 interest and stimulated enormously experi- 

 mental bionomics, I am strongly persuaded 

 that his hypothesis of unit-character fails as 

 a guide to the interpretation of the species 

 and its characters." 



" It is true a great amount of work on 

 Mendelian heredity seems strongly to support 

 the unit-character hypothesis, and that cytol- 

 ogy offers some further support. iN'everthe- 

 less, I have to confess a wholesale scepticism. 

 The germ, as I believe and have long main- 

 tained, stands for an organized whole. It is a 

 unit-organism, not an organism of units; all 

 the features that arise in the course of devel- 

 opment are within the sphere of the individ- 

 ual unity and integral parts of it, and what- 

 ever specificity they possess is completely 

 determined and not of independent origin." 



" The strongest suggestion of unit-char- 

 acters is found in the phenomenon known as 

 segregation. I do not understand the im- 

 portance of this striking behavior of so-called 

 alternative unit-characters. I am familiar 

 with it and deeply interested; but I am un- 

 able to see in them the stmi total of all we 

 know about heredity. What I have said in 

 regard to unit-character applies to the Men- 

 delian doctrine. Mendelism, like mutation, 

 neglects the natural history of the characters, 

 it experiments with and is not primarily con- 

 cerned to know how characters have orig- 

 inated and multiplied." 



