THE CHROMOSOMES 137 



characters are due to peculiarities of the eggs before 

 they are laid. 



The serosa on the other hand is a cellular membrane 

 that develops around the embryo and produces pig- 

 ment. The pigment seen through the shell gives the 

 embryo a definite color, which in the hybrid embryo 

 is characteristic of the maternal race. Since the 

 serosa pigment is not present in the egg, but develops 

 after fertilization the inheritance here appears to be 

 determined by the character of the egg and not by the 

 sperm. But the genetic history of this character of 

 the embryo is apparently the same as that of the 

 color of the shell or of the yolk. It can, therefore, be 

 interpreted in the same way. There must, then, 

 be present in the egg some substance that is at first 

 uncolored, and later this substance when carried into 

 the serosa produces pigment, presumably by inter- 

 acting with something else there. In the next genera- 

 tion, however, the influence of the father comes to 

 light when the F 2 embryo produces its serosa mate- 

 rial; for now the nucleus of the PI male has had op- 

 portunity to determine what this material may be, 

 and should the paternal factor be the dominant one 

 it determines the kind of material that the eggs will 

 contain and hence the color of the serosa of this new 

 generation. 



A case of cytoplasmic inheritance has been de- 

 scribed by Correns in the four-o'clock, Mirabilis 

 jalapa. There is a race whose leaves are checkered 

 with green and white, but some branches may have 

 leaves entirely green, other branches may have only 



