CHEMICAL PHENOMENA IN LIFE 



of this characteristic in the ancestors. There is 

 no doubt that chemical atavism will frequently 

 be found in connection with morphological 

 atavism. We need only think of the reappearing 

 characteristic of the uncultivated ancestors of our 

 fruit trees. But it is not yet known whether such 

 chemical atavisms can reappear without being 

 accompanied by morphological atavism. 



Finally, we have to turn our attention to the 

 variations which are caused by external influences. 

 Botanists well know that the size and thickness of 

 leaves depend upon the intensity of the sunlight 

 in which they have grown. Especially the in- 

 tensity of light, but also the degree of moisture 

 in the air, gravity, mechanical and chemical 

 influences cause very remarkable alterations in 

 the morphological characteristics of plants. At 

 the same time chemical alterations must take 

 place, and we see at last from all the research work 

 which has been carried out in that domain, that 

 the variation is not merely a morphological one, 

 but is also chemical. One must feel it to be a great 

 gap in biological work that chemical properties in 

 their dependence on the physical and chemical 

 influences of their surroundings have not yet been 

 investigated for themselves alone. But a number 

 of facts show even now that chemical variation 

 depends on the influence of environment, and that 

 it shows a similar purposive tendency towards 

 adaptation to the environment, as is known in 

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