ONTOGENESIS 195 



realize in the completed work: he works toward a 

 definite end, and his preliminary efforts are con- 

 ditioned by the sort of final result he wishes. To 

 many observers the processes of development seem 

 equally conditioned upon the nature of the final 

 result, and it is hard to see how such events could 

 come to pass without the help of some guiding 

 agency, like the sculptor in the previous comparison. 

 Such a point of view is called teleological. Human 

 action is so constantly purposive that the untrained 

 mind unconsciously reads into all the activities of 

 Nature a similar purpose. A bygone generation, 

 but by no means an unintellectual one, could see 

 no way of accounting for the movements of sun, 

 moon, and planets except by postulating the assist- 

 ance of angels who pulled and pushed them along 

 their appointed courses. With the increase of 

 knowledge of celestial mechanics it became clear 

 that the intervention of the imaginary angels is 

 not necessary, and the explanation of the move- 

 ments of heavenly bodies became an impersonal or 

 mechanical one. In the same way, to " explain " 

 the complex processes of development, it is not 

 necessary to call upon the guiding help of some 

 hypothetical vital force, even though our knowl- 

 edge of developmental mechanics is still far too 

 inadequate to explain the observed phenomena. 



One of the most prominent students of the rela- 

 tions of plants to their surroundings 1 says : " Each 

 year the list of ' vitalistic activities ' of plants 



i H. C. Cowles. 



