4o6 THE GERM-PLASM 



Guinea dog, for ' they do not become covered with hair when 

 transported to a temperate climate/ * 



Many climatic varieties of plants may also be due wholly 

 or in part to the simultaneous variation of corresponding de- 

 terminants in some part of the soma and in the germ-plasm of 

 the reproductive cells, and these variations must of necessity 

 be hereditary. Temperature, and nutrition in its widest sense, 

 affect the whole body of the plant, — the somatic-cells as well as 

 the germ-cells. It cannot, however, at present be stated whether 

 the determinants in the soma are in this case influenced more 

 strongly than those which are still in the germ-plasm. It is 

 conceivable, and, I am inclined to think, even most usual, that 

 certain determinants are affected to the same extent whether 

 the influence of the environment happens to act on them in the 

 germ-plasm, or in any stage of somatic transformation. In this 

 case the change may have been perhaps scarcely or not at all 

 noticeable in the first generation, and may gradually have become 

 apparent, and also transmissible, in the course of subsequent 

 generations. On the other hand, there are probably many 

 influences of environment which produce a considerable change 

 in the body of the plant, without, however, modifying the cor- 

 responding determinants in the germ-plasm. The experiments 

 made by Nageli and many others on the genus Hieracium at 

 any rate support this view, though they have hardly been carried 

 on long enough to exclude the possibility of a very faint and 

 gradual alteration occurring in the germ-plasm. 

 I The question as to which influences are capable of simul- 

 taneously modifying the developing and growing soma and the 

 corresponding determinants in the germ-plasm, even in a very 

 different degree, can only be solved by future experiments. The 

 / 1 cases of an apparent inheritance of somatogenic variations are 

 due to this coincidence ; — no others are, it seems to me, con- 

 ceivable. All those influences, however, such as the use and 

 disuse of a part, which can only affect this part itself in a specific 

 manner, are incapable of producing a corresponding change in 

 the respective determinants of the germ-cells, and consequently 

 cannot lead to hereditary modifications. In such cases the 



* Compare also the cases of degeneration in the descendants of the 

 European dog in India, which have been carefully collected by Darwin in 

 his ' Variation of Animals and Plants under Domestication,' Vol. I., p. 45. 



