But now, although there is no evidence in support of this postulate, there is no small amount of evidence against it. For this evidence goes to indicate that no small amount of reciprocal action habitually takes place between body-tissues and germinal elements: indeed it seems almost to prove that the orbits of germ-plasm and somato-plasm are not mutually exclusive, but touch and cut each other to a considerable extent. The evidence in question, it will be remembered, is derived from the effects of puberty, senility, castration, &c.; the occasional effect of pollenization on the somatic tissues of plants; the influence which a stock occasionally exercises upon a scion, or _vice versa_, which proves the possibility of a transmission of hereditary characters by a mere grafting together of somatic tissues; the direct evidence given by De Vries that in certain Algae constituents of cellular tissue pass immediately from the maternal ovum to the daughter organism; and the evidence, both direct and indirect, which remains to be given on a larger scale in my subsequent volume, where we shall have to challenge the validity of Weismann’s fundamental postulate touching the non-occurrence of Lamarckian factors in any of the multicellular organisms. It must here again be noticed that in those passages where he concedes the possibly “occasional” transmission of acquired characters Weismann is annihilating his own theory, root and branch. Thus, for example, in allusion to De Vries’ observation just mentioned, he says that we cannot exclude the possibility of “changes being induced by external conditions in the organism as a whole, and then communicated to the germ-cells after the manner indicated in Darwin’s hypothesis of pangenesis.” But it is obvious that the theory of germ-plasm _must_ “exclude the possibility of such a transmission occasionally occurring”; for the very essence of that theory consists in its postulating a difference between germ-plasm and the general body-substance _in kind_, such that there never _can_ be any “communication” from the one to the other “after the manner indicated by Darwin’s hypothesis of pangenesis.” Any prevarication over this point amounts simply to abandoning the theory of germ-plasm altogether, and opening up a totally distinct issue—namely, the _relative importance_ of natural selection and the Lamarckian factors in the process of organic evolution. It may be perfectly true—and I myself believe it is perfectly true—that Darwin attributed too large a measure of importance to the Lamarckian factors; but whether or not he did so is quite a different question from that which obtains between his theory of pangenesis and Weismann’s theory of germ-plasm. The former question is whether we are to “_modify_” the theory of pangenesis, so as to constitute it the theory of stirp; the latter question is whether we are to “_abolish_” the theory of pangenesis, in favour of its logical antithesis, the theory of germ-plasm. And this