ADAPTIVE VARIATIONS. 373 



greater than that of the land plant leaves, then obvi- 

 ously we should have here a case of both definite varia- 

 tion and indefinite variation. The leaves of the aquatic 

 plant would have varied in the direction of greater 

 length, or would have varied definitely in adaptation to 

 their new environment, but the distribution of their 

 variations about their mean would still be in accord- 

 ance with the laws of chance, or would be indefinite. 



The term " definite," as applied to variations, seems 

 to be generally regarded as more or less synonymous 

 with " adaptive." Thus Lloyd Morgan * defines defi- 

 nite or determinate variations as " variations along 

 special or particular lines of adaptation," while Hen- 

 slow f says " Definite variations are always in the direc- 

 tion of adaptation to the environment itself." Hence 

 it seems to me that the discussion of the definiteness or 

 indefiniteness of variations may, for practical purposes, 

 be narrowed down to the following questions: (1) 

 Have conditions of life an appreciable influence on 

 organisms, and if so, (2) Is this influence in any case 

 cumulative, i. e., partly inherited, and (3) How far are 

 the effects produced adaptive? The first two questions 

 I have already endeavoured to answer in the preceding 

 chapters. The third we will now proceed briefly to 

 inquire into. 



As far as the limited number of observations avail- 

 able can show, adaptability would seem to be a funda- 

 mental property of protoplasm. Whenever an organ- 

 ism is exposed to changed conditions of life, then it is 

 found that the original want of adaptation becomes 

 gradually and progressively diminished with increase 

 * " Habit and Instinct," p. 311. f Ibid., p. viii. 



