INSTINCT AND SENSUOUS COGNITION. 45 



"What has been taken for the effect of 'will' or 'in- 

 stinct' is in reality the effect of light, of gravity, of fric- 

 tion, of chemical forces, etc." And so he speaks of 

 heliotropism, when the direction of the rays of light 

 determines the direction of the movements of an ani- 

 mal or its orientation; of geotropism, when gravity, or 

 of stereotropism, when contact with solid bodies deter- 

 mines the orientation, and so forth. 



Heliotropism, geotropisni, and stereotropism may 

 be positive or negative. They are positive, if the ani- 

 mal's motion is towards the light, the earth, or a solid; 

 negative, if in the opposite direction. In further de- 

 scription of his purely mechanical theory, Prof. I^oeb 

 uses the following altogether "unequivocal" phrases: 

 "By the help of light the botanist controls the orienta- 

 tion of a plant at will. Why should he maintain that the 

 'will' or 'instinct' of a plant [ ! ] cooperates with the rays 

 of light when the orientation is determined solely and 

 unequivocally by the latter? The movements of an ani- 

 mal toward the light are, however, .... identical 

 point for point with the movement of a plant toward 

 the light. Wherever the orientation of plants has been 

 satisfactorily controlled experimentally, light has in- 

 deed been considered the sole determining factor; but 

 in the case of animals, in which in similar experiments 

 light is without doubt also the sole determining factor, 

 'instinct' and 'freewill' [sic!] have still been considered 

 to play a role. ' ' 



that could be interpreted as having any connection whatever 

 with spontaneous generation. Cf. our paper on "Modern 

 Science and the Origin of Life"in the New York Messenger, 

 April, 1906. 



