136 A NEW THEORY OF EVOLUTION. 



will be stunted ; if kept in the dark, its 

 colour will be affected ; and insufficiency of 

 moisture will be evident in the foliage. A 

 plant grown in a valley may change 

 greatly in appearance on a mountain ; and 

 some trees when transported to a colder 

 climate, although they live, may fail to 

 blossom or to mature seed. 



Man can, however, do comparatively little 

 to alter the form, size, or appearance of seed 

 the part of the plant that may be taken 

 to represent the life-force. When the fruit 

 that envelops some seed is greatly developed 

 by high cultivation, both the quantity and 

 fertility of the seed are usually greatly dim- 

 inished, but the appearance of the seed itself 

 is only slightly modified, if at all. On the 

 other hand, the vitality of seed, matured 

 under even highly unfavourable conditions, 

 does not seem to be seriously impaired, for 

 the young plants from such seed readily 

 respond to generous treatment, and may at 

 maturity approach the normal size. It is 

 also remarkable that reproduction is stimu- 

 lated by unfavourable conditions of life : 

 trees growing under adverse conditions yield 

 the largest quantity of seed, and animals 

 in like circumstances are most fertile. 

 Statistics show that the population of Ire- 



