54 EMBRYOLOGY 



are present in the same individual often evolve mechanisms whereby they 

 become self-sterile and thus cross-fertilization takes place. There appears to 

 be a real advantage to cross-fertilization on a long-term basis. It must be 

 emphasized, however, that a pure, healthy, non-varying species once estab- 

 lished suffers nothing from inbreeding or from continued asexual reproduc- 

 tion on a short-term basis. 



