130 Outline of Genetics 



two or more different species. Under such circumstances fila- 

 ments of one species were observed in the act of crossing with 

 filaments of another species. Furthermore, in such mixed popu- 

 lations there were discovered some filaments which were evidently 

 the products of previous crosses, for they clearly showed new com- 

 binations of the characters of two species. It is to be hoped that 

 exact experimental work will prove feasible with this genus. 



One instance of the clean segregation of characters in the 

 gametophyte generation is to be found among angiosperms, 

 Selling's semi-sterility among beans. This wdll be described 

 later in the discussion of the general subject of sterility. For the 

 most part the gametophyte of angiosperms seems to be merely 

 an expressionless intermediate stage between succeeding sporo- 

 phyte generations. As East (i) puts it: ''Modern discoveries 

 tend more and more to show that the sole function of the gameto- 

 phyte of the angiosperms is to produce sporophytes. The char- 

 acters which they carry appear to be wholly sporophytic, the 

 factors which they carry functioning only after fertilization." 



LITERATURE CITED 



1. East, E. M., and Park, J. B., Studies on self-sterility. I. 

 The behavior of self-sterile plants. Genetics 2:505-609. 191 7. 



2. Transeau, E. N., Hybrids among species of Spirogyra. Amer. 

 Nat. 53:109-119.^^5. 7. 1919. 



