HEREDITY 



nearest possible approach to self-pollination is 

 in such cases the mating of brother with sister, 

 or of parent with child. But this is less close 

 inbreeding than occurs in self-pollination, for 

 the individuals mated are not in this case iden- 

 tical zygotes, though they may be similar ones. 



It has long been known that in many plants 

 self-pollination is habitual and is attended by 

 no recognizable ill-effects. This fortunate cir- 

 cumstance allowed Mendel to make his remark- 

 able discovery by studies of garden-peas, in 

 which the flower is regularly self -fertilized, and 

 never opens at all unless made to do so by 

 some outside agency. Self-pollination is also 

 the rule in wheat, oats, and the majority of the 

 other cereal crops, the most important econom- 

 ically of cultivated plants. Crossing can in such 

 plants be brought about only by a difficult 

 technical process, so habitual is self-pollina- 

 tion. And crossing, too, in such plants is of 

 no particular benefit, unless by it one desires 

 to secure new combinations of unit-characters. 



In maize, or Indian corn, however, among 

 the cereals, the case is quite different. Here 

 enforced self-pollination results in small un- 



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