440 THE GERM- PLASM 



did not attach sufficient importance to the variation of the 

 germ-plasm in consequence of influences acting directly ; but 

 the existence of bud-variations does not prove that variation 

 occurs without amphimixis. For all those plants in which bud- 

 variation has been observed are reproduced sexually, and their 

 ithoplasm therefore contains ids and determinants which differ 

 individually : the different intermingling and behaviour of 

 these in the process of growth would alone form a basis for 

 variations. 



In my opinion, indeed, this heterogeneous composition of the 

 germ-plasm produced by amphimixis is an essential factor in 

 bud-variation, notwithstanding the fact that it may not in this 

 case give the first stimulus to variation, any more than it does 

 in ordinary individual variation. Plants which have for a long 

 time been propagated by means of buds and shoots, like the 

 potato and sugar-cane, must possess a germ-plasm consisting 

 of different kinds of ids ; for they were formerly reproduced 

 sexually, and the complex intermingling of their determinants 

 thus produced, cannot have undergone an appreciable modifica- 

 tion during the period in which they have multiplied asexually. 

 Their germ-plasm must therefore present far more favourable 

 conditions for variation than would one composed of identical 

 ids or of one kind of id only, — did such a germ-plasm exist. 



The primary cause of bud-variation must be the same as 

 that of variation from seeds, and must be due to inequality of 

 mitritio7i in the gerni-piasm ; — the term ' nutrition ' being used 

 in its widest sense, so as to include differences in tempera- 

 ture, &c. This view not only receives support from theoretical 

 considerations, — for theoretically it could only be replaced by 

 the assumption of an internal phyletic developmental force, — 

 but it is also supported by observation. For all recorded ob- 

 servations go to prove that bud-variations are most likely to 

 occur when the plant is placed under abnormal conditions, and 

 especially when it is cultivated. As the direct modification of 

 the soma caused by these conditions is not hereditary {Nageli)^ 

 and cannot be so, — for somatic variations are only hereditary 

 when they proceed from the germ. — we are obliged to assume 

 that the modification of several or many determinants in the 

 germ-plasm is due to inequality of nutrition. 



That bud-variations are produced by the same causes as 

 those which occur in reproduction by seeds, is borne out by 



