HYBRIDISM 265 



species (excluding those long cultivated) which have not had 

 their reproductive systems in any way affected, and they are not 

 variable; but hybrids themselves have the reproductive systems 

 seriously affected and their descendants are highly variable. 



But to return to our comparison of mongrels and hybrids: 

 Gartner states that mongrels are more liable than hybrids to re- 

 vert to either parent form; but this, if it be true, is certainly only 

 a difference in degree. Moreover, Gartner expressly states that 

 the hybrids from long cultivated plants are more subject to re- 

 version than hybrids from species in their natural state; and thi§ 

 probably explains the singular difference in the results arrived 

 at by different observers. Thus Max Wichura doubts whether 

 hybrids ever revert to their parent forms, and he experimented 

 on uncultivated species of willows, while Naudin, on the other 

 hand, insists in the strongest terms on the almost universal tend- 

 ency to reversion in hybrids, and he experimented chiefly on 

 cultivated plants. Gartner further states that when any two spe- 

 cies, although most closely allied to each other, are crossed with 

 a third species, the hybrids are widely different from each other; 

 whereas if two very distinct varieties of one species are crossed 

 with another species, the hybrids do not differ much. But this 

 conclusion, as far as I can make out, is founded on a single ex- 

 periment, and seems directly opposed to the results of several 

 experiments made by Kolreuter. 



Such alone are the unimportant differences which Gartner is 

 able to point out between hybrid and mongrel plants. On the 

 other hand, the degrees and kinds of resemblance in mongrels 

 and in hybrids to their respective parents, more especially in 

 hybrids produced from nearly related species, follow, according 

 to Gartner, the same laws. When two species are crossed, one 

 has sometimes a prepotent power of impressing its likeness on the 

 hybrid. So I believe it to be with varieties of plants; and with 

 animals, one variety certainly often has this prepotent power 

 over another variety. Hybrid plants produced from a reciprocal 

 cross generally resemble each other closely, and so it is with mon- 

 grel plants from a reciprocal cross. Both hybrids and mongrels 

 can be reduced to either pure parent form by repeated crosses in 

 successive generations with either parent. 



These several remarks are apparently applicable to animals, 

 but the subject is here much complicated, partly owing to the 

 existence of secondary sexual characters, but more especially 

 owing to prepotency in transmitting likeness running more 

 strongly in one sex than in the other, both when one species is 



