134 OTHEE FACTORS OF EVOLUTION 



new conditions, that the replacing of it in its old habitat should 

 cause it to go through the reverse set of changes, leading to a 

 resumption of its original form and characters.' 



The plasticity of plants has long since been shown to be most 

 remarkable, alike from the extent and the rapidity of the varia- 

 tions that have been induced. Thus in a previous article 

 Prince Kropotkin cited numerous experiments showing remarkable 

 alterations induced in plants by changes in their environment : 

 transferring them, for instance, from the lowlands to mountain 

 elevations ; subjecting others to a deficiency of light ; or exposing 

 them to a very dry air and so producing prickles by gradually 

 diminishing the size and development of the leaves. In this latter 

 case the growth of plants in different degrees of moisture of itself 

 seemed to produce the structures best adapted for avoiding ex- 

 cessive evaporation. So that, as was said by Kropotkin, " several 

 adaptations which were considered as slowly accumulated acci- 

 dental variations, can be obtained very rapidly — as a direct result 

 of environment itself." Vernon, indeed, in his work on "Variation 

 in Animals and Plants," 3 feels warranted in saying that " adapta- 

 bility would seem to be a fundamental property of protoplasm " ; 

 and in the pages indicated he cites numerous cases in illustration 

 of this view from experiments of different kinds made with plants. 

 It is true that in some of these cases the question arises whether 

 the indirect influence of external conditions, that is ' natural selec- 

 tion,' may not also have been operative {loc. cit. p. 391). 



Although the influence of change in the environment does not 

 produce such rapid and marked effects upon animals as it does 

 upon plants, it is none the less a cause of change in them. 

 Differences in quantity or quality of food, or of both combined, are 

 among the most potent of these slowly acting causes. Thus Prof. 

 Brewer of Yale University says : " Breeders do not believe that 

 the characters acquired through the feeding of a single ancestor, 

 or generation of ancestors, can oppose more than a slight resistance 

 to that force of heredity which has been accumulated through 

 many preceding generations, and is concentrated from many lines 

 of ancestry. Yet the belief is universal that the acquired characters 

 due to food during the growing period has some force, and that 



' Such phenomena are thoroughly well known and recognised in regard to 

 Bacteria ; while L. Errera, Klebs and others have shown that similar phenomena 

 are to be met with among Fungi. 



' "Nineteenth Century," April, 1894, pp. 688-691. 



3 Internl. Sc. Series, 1903, pp. 373-378. 



