220 



PPIYSICAL BASIS OF HEREDITY 



branches give only white offspring. Flowers on the check- 

 ered branches give some clieckered plants, some white 

 plants and some green plants. The proportions in which 

 these different types arise varies according to the amount 

 of green in the branch from which the selfed seed came. 

 "When the ovary of a flower on a green branch is fertil- 

 ized by pollen from a white branch, the plant produced 

 is green like the maternal branch. If the ovary of a 

 flower on a white branch is fertilized by pollen from a 



a ^ b 



Fig. 102. — Green leaf and checkoied leaf of four-o'clock. (After Baur.) 



green branch the offspring is white like the maternal 

 branch. These and other combinations show that this 

 color inheritance is only through the mother. The results 

 are explicable on the assumption that there are normal 

 (green) chlorophyll bodies and abnormal chlorophylless 

 bodies, both kinds propagating in the cytoplasm by divi- 

 sion, and that these two kinds are transmitted only through 

 the egg-cell. The green or white color of the leaves of a 

 given branch is an index of the kind of chlorophyll body 

 that the ovaries will probably contain. At each division 

 of the body-cells the chloro|)hyll grains present in it are 

 sorted out more or less at random — hence from a cell that 



