LAWS OF EVOLUTION OF THE PLANT KINGDOM. 39 



were, prepares the way for the former, namely, 

 ampliation, by virtue of which the growth of the 

 whole ontogeny or of single stages of it undergoes a 

 quantitative increase, so that an organ acquires a 

 greater number of cells, and an individual a greater 

 number of organs. After this increase in number of 

 parts in a stage of ontogeny, differentiation follows 

 as far as the nature of the functions permits, by the 

 parts most separated passing into each other by 

 intermediate gradations. By the further phyloge- 

 netic process of reduction the intermediate forms are 

 suppressed. At last only the extreme products of 

 differentiation lie near each other in space or follow 

 upon each other in time ; and these products are as 

 limited in quantity and number as possible. 



Along with the above named phylogenetic proc- 

 esses, which take place by the automatic increase 

 of the idioplasm, external influences are always 

 active. These lend to the organism at times a local 

 stamp corresponding to its environment, and follow 

 the law of adaptation. 



21. ALTERNATION OF GENERATIONS IN RELATION TO 



PHYLOGENY. 



Since the simplest plants are cells and the more 

 complex ones are formed from cells, a whole phy- 

 logenetic line may be regarded as a series of cell 

 generations following one after another. In the 

 lowest forms all cell generations are like each other; 



