External and Internal Factors in Evolution 329 



which, according to my view, bring forth beyond a doubt 

 adaptive changes." 



The external influence of climate and of food act only as 



fffansitory factors. A rich food supply produces fat, lack 

 of food leads to leanness, a warm summer makes a plant more 

 aromatic, and its fruit sweeter ; a cold year means less odor 

 and sour fruit. Of two similar seeds the one sown in rich 

 soil will produce a plant with many branches and abundance 

 of flowers; the other, planted in sandy soil, will produce a 

 plant without branches, with few flowers, and with small 

 leaves. The seeds from these two plants will behave in 

 exactly the same way; they have inherited none of the 

 differences of their parents.? ,' Influences of this sort, even if 

 extending over many generations, have no permanent effect. 

 Alpine plants that have lived since the ice age under the 

 same conditions, and have the characters of true high- 

 mountain plants, lose these characters completely during the 

 first summer, if transplanted to the plains. Moreover, it 

 makes no difference whether the seed or the whole plant 

 itself be transferred. In place of the dwarfed, unbranched 

 growth, and the reduced number of organs, the plant when 

 transferred to the plains shoots up in height, branches strongly, 

 and produces numerous leaves and flowers. The plants retain 

 their new characters as long as they live in the plain without 

 any other new variation being observed in them. 



Other_characteristics also, which arise from different kinds 

 of external influences due to differentiocalities, such as damp- 



"hess and shade, a swampy region, or different geological 

 substrata, last only so long-as Jbe external conditions last. 



These, transient peculiarities make up the characters of 

 local varieties. That they have no permanency is intelli- 

 gible, since they exhibit no new characters, but the change 

 consists mainly in the over- or under-development of those 

 peculiarities that are dependent on external influences. The 

 effect of these influences may be compared to an elastic rod, 



