.s,,. DR. WEI SM ANN'S THEORY OF HEREDITY. i8i 



except indirectly ;'5 but I " proved " it by appealing to the argument 

 of the accumulation of probabilities, based on innumerable coinci- 

 dences and correlations. 



Now, however. Dr. Weismann has provided me with an 

 unlooked-for support, supposing such to be necessary, because he 

 insists upon the action of the environment being directly on the 

 germ-plasm of the germ-cells. He thus speaks: — "There only 

 remains one principle by which we can explain the transformation 

 of species — the direct alteration of the germ-plasm " (p. 388), or 

 " the direct change in the germ-plasm affected by external influences, 

 using these words in their widest signification" (p. 411), and " we 

 must include everything which is not germ-plasm " (p. 396). 



In flowers visited by insects, the ovules and pollen-grains are 

 both prepared and ready at the very time the insect arrives. Its 

 irritating action is directly upon the anthers and stigma, which is 

 in immediate communication with the ovule, embryo-sac, and egg- 

 nucleus ; so that it is impossible to conceive of a closer contact than 

 that which thus obtains between the insect and the germ- and 

 sperm-cells. 



If, therefore, it be necessary, in order that the peculiarities of 

 flowers should be hereditary, that the influence of the irritations be 

 directly upon the germ-cells, then the conditions for securing such are 

 exactly those which every flower that is in adaptation to insect 

 fertilisation supplies. 



With regard to the origin of new specific characters by sexuality. 

 Dr. Weismann observes that " permanent hereditary variability may 

 follow from the varied combinations which are due to the mixture 

 of two individually distinct germ-plasms at each act of fertilisation " 

 (p. 327), And again : " Variability depends upon sexual repro- 

 duction '" (p. 293).^^ 



When, however, we perceive the constancy of specific characters 

 of plants growing wild. Nature does not seem to supply any 

 encouragement to the acceptance of this idea. Not only are the 

 species of plants named by Linnaeus just as they were in his day, 

 but Dr. Weismann calls the reader's attention to the fact that 

 species of plants in Egypt have remained unchanged for thousands 

 of years ; while he refers also to arctic plants, now widely dispersed, 

 %vhich are probably very much the same as they were at the Glacial 

 Epoch. 



On the other hand, had he alluded to varieties and hybrids, there 

 would have been more to be said in his favour, as the successive 

 generations of such, under cultivation at least, vary immensely ; but 

 their variations mainly refer to size and colour, and only to a limited 

 degree in form, e.g., " Pelorian " varieties. 



13 See op. cit., chap, xiv., on "Acquired regularity and Peloria," p. 128. 

 !'■ A theoretical description is given on p. 321. 



