18 METHODS OF EVOLUTION [CHAP. 



merely assuming that they arose out of 

 " individual differences," and then, taking for 

 granted that the "fittest to survive out of 

 indefinite variations" would be hereditary. It 

 is my object to show how variations do arise, 

 viz. : by the plant responding to changed con- 

 ditions of life:, and, secondly, that the altered 

 structures in adaptation to the new environ- 

 ment do become hereditary, if the plants, genera- 

 tion after generation, continue to live long enough 

 in the new surroundings. That is the true and 

 only method of Evolution. 



The response usually shows itself at once, 

 i.e., as soon as growth commences under the 

 new conditions. As the soma or vegetative 

 system precedes the appearance of the repro- 

 ductive organs, the influence or " direct action," 

 as Darwin called it, is solely upon it, but the 

 effects lie dormant till the reproductive organs 

 put in an appearance. It may be a year after- 

 wards, as in biennials, or longer still, even 

 years, as in trees, when the seeds ripen, so 

 that it is not till the following, the second, or 

 other year that the original effects reappear in 

 the offspring. 



The exact or immediate origin of "sports," 

 i.e., the sudden appearance of some very well- 

 marked structure, colour, etc., in parts of plants 

 or in seedlings, cannot always be traced, and at 

 present must be assumed from our positive 



