VARIATION 35 



extrinsic factor of food supply, was able to modify 

 the height of the "head" of the microscopic fresh- 

 water crustacean, Hyalodaphnia, in the remarkable 

 manner indicated in Figure 9. When poor food was 

 supplied, the percentage of the head height to that 

 of the body averaged hardly forty, while with rich food 

 it was increased to over ninety. 



Similarly Klebs succeeded in changing at will the 



35 40 45 50 55 60 65 70 75 80 85 90 95 100 # 

 Ratio of height of head to length of shell ' * 



Fio. 9. Schematic curve of the head height of Hyalodaphnia 

 under various conditions of nourishment. Adapted from 

 Woltereck. 



number of stamens in the common "live-for-ever," 

 Sedum spectabile, by manipulating the environment in 

 which the plants were kept. Some of his results are 

 shown in Figure 10. Curve A combines the data for 

 4260 flowers which were raised in well-fertilized dry 

 soil under bright light ; curve B represents 4000 flowers 

 grown in a moist greenhouse under red light ; and 

 curve C includes 4390 flowers from well-fertilized soil 

 in moist hotbed conditions under a weak light. 



c. Weismawi, on the contrary, believes that the 



