54 



GENETICS 



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 29. When poor food 



Number of 

 Fl 



FIG. 30. Variations in the number of stamens in the flowers of the " live- 

 for-ever" (Sedum spectabile) under various controlled conditions. 

 For detailed description, see text. After Klebs. 



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 

 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 30. Polygon A combines the 

 data for 4260 flowers which were raised in well-fer- 

 tilized dry soil under bright light ; polygon B repre- 

 sents 4000 flowers grown in a moist greenhouse 

 under red light ; and polygon C includes 4390 flowers 



