Page:Popular Science Monthly Volume 45.djvu/191

Rh But this was only a beginning of the almost complete retreat that he has now made in his last work on the Germ-Plasm. As before, it seems to have been the phenomena which the vegetable kingdom presents that most obstinately refuse to adapt themselves to the mechanical theory of heredity of which he is the author. Before these facts his fundamental distinction between the blastogenic and the somatogenic idioplasm breaks down completely, and here at least he is "compelled to assume that most, if not all, of the cells contain all the primary constituents of the species in a latent condition." After carefully considering such cases as those of Bryophyllum and Begonia, almost any part of which may be made to grow if properly situated, he admits that such observations "apparently prove that 'every small fragment of the members of a plant contains the elements from which the whole complex body can be built up, when this fragment is isolated under suitable external conditions.'"

Before passing to the major admissions of Weismann it may be well to mention a few of the "doubtful phenomena of heredity" which, in case they really occur, form such a stumbling block to his system. On this side of the water one is amused at the statement that "blue grains occasionally occur among the yellow ones in cobs of the yellow-grained maize (Zea) after fertilization with the pollen of a blue-grained species." There is probably only one "species" of Indian corn, but the cultivated varieties are endless, and every farmer's boy knows that it is of the greatest importance to keep these apart, so that the ears will "fill" with the same kind of kernels. Few American farmers would hesitate to stake their farms on the much more than "occasional" occurrence of different kinds of kernels on the same cob in a field where different varieties are planted together.

As regards the numerous cases of the alleged transmission of characters derived from one sire to the offspring of a subsequent sire, though disposed to discredit the evidence, he nevertheless admits their possibility to a limited extent. For he says of them: "We may, however, at any rate suppose that this so-called 'infection,' if not altogether deceptive, only occurs in rare instances, and by no means regularly, or at most only in some cases."

Here we have again, as in the general case above considered, a characteristic Weismannian argument, shifting the point from the qualitative to the quantitative, from the principle to the degree, which reminds one very forcibly of Jack Easy's wet nurse