THE MUTATION THEORY AND MUTATIONS. 159 



respects from its parents. The difference is labeled a "discontinuity"; i.e., the 

 offspring is assumed to have obeyed the law of heredity in so far as it resembles 

 the parental stock, and to have jumped hereditary bonds in so far as it departs from 

 such resemblance. The "jump" signifies a sudden, unmediated translation from 

 one sphere of existence into another. To put it in another way, the organism, in 

 its germ state, makes a shift from the ancestral track to a new track, without a 

 connecting switch. As immutability of species is held to be incompatible with 

 gradual convergence or divergence, the mutant is conceived as set off at one stroke 

 and at full distance, and so it must henceforth run its course exactly parallel to 

 that of the parent species. 



This conception is obviously the negation of a branching genealogical tree. In- 

 stead of a tree with a single trunk and many divergent branches, we have only 

 naked, branchless stems, shooting up from different levels and to different heights, 

 around the original central type. 



The terms "discontinuity" and "mutation," as used by de Vries and Bateson, 

 have their significance fixed in one and the same idea that of unit-characters. 

 However small the variations to which they apply, these never become synonymous 

 with slow, cumulative variations. The whole theory of mutation would fall if in 

 a single case the assumed discontinuity could be covered by transitional gradations. 

 Although de Vries suggests that mutations may be provisionally compared with 

 chemical substitutions, he nowhere confounds the mutation with ordinary chemical 

 changes that underlie development, differentiation, and all so-called vital proc- 

 esses. To do so would of course annul all distinction between variation and muta- 

 tion, between qualitative and quantitative changes, or between continuity and 

 discontinuity. 



In order to realize how indispensable to the whole mutation fabric is this unit- 

 character concept, let us glance at its history for its source and its alleged justifi- 

 cations in facts. 



As to its source, we have only to turn to an earlier work of de Vries, his "Intra- 

 cellular Pangenesis" (1889), to learn that the concept comes directly from Darwin's 

 discarded "Hypothesis of Pangenesis." De Vries recognized two distinct parts in 

 the hypothesis, one of which is designed to account for the transmission of acquired 

 characters, the other for the transmission of hereditary characters through the 

 germ-cells. 



With Weismann, de Vries denies the transmissibility of acquired characters; 

 but he accepts the other part of the hypothesis, together with the idea that adult 

 characters are represented in the germ-cell by distinct unit-elements. 



Darwin's assumption that every cell in the body from the inception of germ- 

 life to the end of development, and on to the end of mature life, is continually 

 throwing out inconceivably small "gemmules" or unit-characters, that in some mys- 

 terious way are distributed not only to the reproductive cells, but to all other cells 

 of the body, stretches the idea of transmission to the brink of absurdity. To elimi- 

 nate the whole soma from the field of such emission and distribution, and thus 

 limit transmission to the reproductive cells, was surely a long step; but the myth 

 of transmission was not eliminated; it was only reduced in its field. The pangenesis 

 of the whole body became the " intra-cellular pangenesis" of the germ-cell. Trans- 

 mission thus became more direct, but its mysteries remained as unfathomable as 



