VARIATION 439 



quent amphimixis were capable of reducing the modified deter- 

 minants to a minority, and even of removing them completely 

 from the germ-plasm. The modification of the determinants 

 manifestly occurs very gradually, as the small number of modi- 

 fied flowers in most of the years shows ; and the chances must 

 have been greatly in favour of the union in amphimixis of 

 eerm-cells which contained few or no modified determinants. 



Had fertilisation been produced artificially, and abnormal 

 flowers always employed for the purpose, it would have been 

 easv in the course of a moderate number of generations to 

 modify the species entirely, and these cases would then have 

 served as an illustration of the process of natural selection. It 

 would have been still easier to produce the contrary eff"ect by 

 selection. — that is to say. to keep the species constant, and 

 suppress any subsequent variation in this direction. For in the 

 present instance, variation evidently occurred slowly, and most 

 of the determinants were not easily affected by it ; and these 

 experiments furnish additional proof of the truth of the statement 

 propounded above that the elements of the germ-plasm only 

 change slowly, and with difficulty : they merely fluctuate to a very 

 slight degree, and only undergo an important change of any 

 duration when uniform influences continue to act on them in one 

 direction for a longer time. 



It by no means follows from what has just been said that 

 influences of environment and nutrition exist, which, when they 

 have acted for a long time, are able to modify the majority 

 of the determinants for certain parts of the body, and thus to 

 produce purely climatic variations, in the origin of which natural 

 selection has no share. Many — perhaps even most — of the 

 'climatic' varieties are rightly so called. 



Suchsudden variants, however, appear not only in ^z///;-^ plants 

 which have been produced sexually, but also in the individual 

 shoots of a plant. These bud-variations are rarely met with ; 

 but in cases in which they occur, they can be propagated by 

 cuttings or grafting, and often even by seeds. 



When I ventured some years ago to suggest that sexual 

 reproduction has come into force in organic nature in order to 

 preserve the variability which had existed since the time o\ 

 the primordial beings, facts concerning bud-variation were put 

 forward by several persons to prove that variability may occur 

 in the absence of sexual reproduction. At that time 1 certainly 



