CHAP. XIL GENERAL RESULTS. 469 



crossed species are subjected. A plant's own pollen 

 is strongly prepotent over that of any other species, 

 so that if it is placed on the stigma some time after 

 foreign pollen has been applied to it, any effect from 

 the latter is quite obliterated. It is also notorious 

 that not only the parent species, but the hybrids 

 raised from them are more or less sterile ; and that 

 their pollen is often in a more or less aborted con- 

 dition. The degree of sterility of various hybrids 

 does not always strictly correspond with the degree of 

 difficulty in uniting the parent forms. When hybrids 

 are capable of breeding inter se, their descendants are 

 more or less sterile, and they often become still more 

 sterile in the later generations ; but then close inter- 

 breeding has hitherto been practised in all such cases. 

 The more sterile hybrids are sometimes much dwarfed 

 in stature, and have a feeble constitution. Other 

 facts could be given, but these will suffice for us. 

 Naturalists formerly attributed all these results to 

 the difference between species being fundamentally 

 distinct from that between the varieties of the same 

 species ; and this is still the verdict of some naturalists. 

 The results of my experiments in self-fertilising and 

 cross-fertilising the individuals or the varieties of the 

 same species, are strikingly analogous with those just 

 given, though in a reversed manner. With the majority 

 of species flowers fertilised with their own pollen yield 

 fewer sometimes much fewer seeds, than those ferti- 

 lised with pollen from another individual or variety. 

 Some self-fertilised flowers are absolutely sterile ; but 

 the degree of their sterility is largely determined by 

 the conditions to which the parent plants have been 

 exposed, as was well exemplified in the case of Esch- 

 scholtzia and Abutilon. The effects of pollen from the 

 same plant are obliterated by the prepotent influence 



