328 ORIGIN OF SPECIES 



fails under these circumstances to perform its proper func- 

 tion of producing offspring closely similar in all respects 

 to the parent-form. Now hybrids in the first generation are 

 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 their 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 eitlier parent-form; but this, if it be true, is cer- 

 tainly only a difference in degree. Moreover, Gartner ex- 

 pressly states that hybrids from long cultivated plants are 

 more subject to reversion than hybrids from species in their 

 natural state; and this probably explains the singular differ- 

 ence 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; whilst Naudin, on the other hand, insists in the 

 strongest terms on the almost universal tendency to reversion 

 in hybrids, and he experimented chiefly on cukivated 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 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 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 cer- 

 tainly often has this prepotent power over another variety. 

 Hybrid plants produced from a reciprocal cross, generally 



