EXTERNAL INFLUENCES AS CAUSES OF VARIATION 253 



To these conclusions two observations may well be added for 

 present purposes : 



i. Heliotropism, like many other reactions of protoplasm, 

 arises from the nature of the organism, and not necessarily from 



11:22 



i 



V" 



d 



(2). 14:OO to 14:2O 



11:12 



11:02 



10:55 



10:44 



12:49 



14:21 



10:28 



14:24 



14:19 



(3). 14:20 to 14:34 



FIG. 28. Effect of light upon locomotion : 

 movements of an amoeba in response 

 to changing directions of .light. Ar- 

 rows show the direction of the light 

 rays, and figures show the hour (13= i 

 o'clock, etc.). After Davenport 



12:54 



'(1). 12:48 to 14:00 



a basis of utility. For example, roots are in general positively 

 heliotropic, a quality that is not of the slightest usefulness, 

 and which must be regarded as entirely accidental. Again, this 



