288 HYBRIDS AND MONGRELS COMPARED. 



descended from 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 revert 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 reversion than hybrids from species in 

 their natural state ; and this 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 tendency to 

 reversion in hybrids, and he experimented chiefly on culti- 

 vated plants. Gartner further states that when any two 

 species, although most closely allied to each other, are 

 crossed with a third species, the hybrids are widely differ- 

 ent 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 experiment, 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 

 eertainly 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 

 mongrel plants from a reciprocal cross. Both hybrids and 

 mongrels can be reduced to either pure parent form by re- 

 peated crosses in successive generations with either parent. 



These several remarks are apparently applicable to ani- 

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



