548 



THE AMERICAN NATURALIST [You LIII 



have been propagated by self-fertilization for several generations, a 

 single cross with a fresh stock restores their pristine vigor, and we 

 have a strictly analogous resnlt with our domestic animals. The good 



succeeding generations. But this may merely be that crossed plants of 

 like any other character to their successors (lb, 438). 



In this paragraph Darwin calls attention to a fact that 

 attracted little attention for a generation, — viz., the im- 

 mediate improvement due to a cross. Darwin was thus if 

 not the first to call sharply to attention, the matter of the 

 relatively increased size and vigor of first generation 

 hybrids, at least the first to subject the question to exper- 

 imental analysis. 



So far as plant hybrids are concerned, Darwin's mind 

 was chiefly occupied, as we have seen, not so much with 

 the fundamental theory of hybrids, as with the question 

 of sterility in hybrids and its inheritance. The general 

 question of what is the essential nature of hybridity, and 

 liow and in what manner the characters are distributed in 

 the ]i\i)rid offspring, seems not to have come to an issue 

 wilhiiim. 



However, among tlie matters of interest to modern stu- 

 dents of genetics are his recognition of tlic ucncral fact 

 of the interraediacy of hybrids, and of the occasional 

 complete dominance of one or tlie otlici' set of parental 

 characters, together with the phenomena which lie terms 

 ''reversion." Eegarding the former matter he remarks : 



In regard to tlic l.cliavioi- of rl,ai'a<-tcrs in cro>scs, while 

 admittinu- tliat, in tlii' ina.j<.rily of ca>cs. \\w liyl.rid off- 

 spring arc intcrinc(liatc between tlu'ii- parent^, lie recog- 

 nized that certain cliaracter> are incai)al)le of fusion. 



