VARIATION 441 



the fact that the former occur most frequently in those species 

 which have already varied greatly in multiplying by seeds.* 

 Expressing this in terms of the idioplasm, we may say that 

 it occurs oftenest /;/ tJiose species in luhich the hoifiologoiis 

 determinants already exhibit considerable differences. 



We attribute these variations to influences of nutrition, which 

 at first bring about slight, and then more marked deviations in 

 certain determinants of the germ-plasm during the course of their 

 growth and multiplication, if these influences continue ; but this 

 alone does not fully account for the process. The question then 

 arises as to how the modifying influences can cause a particular 

 bud to undergo variation while all the rest remain unchanged, 

 although they are exposed to the same influence. Some other 

 influence is therefore required before a modification of this 

 kind can appear. 



If we remember that bud-variations sometimes occur in wild 

 plants, or in those which, like the forest-trees of our parks, 

 exist under practically the same conditions as many wild ones, 

 it will appear still more probable that the inequalities of nutri- 

 tion, while constituting the primary cause of bud-variation, 

 cannot alone bring it about. 



My own conception of the process is as follows. Just as 

 in the case of ordinary individual variation, bud-variation is 

 primarily due to those slight, fluctuating, structural changes 

 which all determinants undergo in consequence of minute and 

 inevitable fluctuations in nutrition. As in the former case, the 

 homologous determinants of the various ids are not all affected 

 to the same extent ; some become greatly modified, and others 

 little or not at all. A difference is, however, seen in the fact 

 that in this case the same influence of change — e.g., generally 

 improved nutrition — occurs for a considerable time, and through- 

 out several genejations. As in the case of variations in plants 

 raised from seeds, a modification of greater extent can thus be 

 produced in these determinants. 



Up to this point the process is quite similar to that of the 

 spasmodic variation of seedlings. A difference, however, results 

 owing to the non-occurrence of amphimixis in the case of gem- 

 mation, for the variable bud does not arise from the germ-plasm 

 of a seed, but from ^ blast ogenic'' gervi-pias?n (' Knospen-Keim- 



* Danvin, loc. cit. 



