Cii4.r. VIII. IIVIJRIDS AND MONGRELS COMPARED. ogi 



those from very distinct species ; and this shows that the dif- 

 ference in the degree of variability graduates away. When 

 mongrels and the more fertile liybrids are propagated for sev- 

 eral generations, an extreme amount of variability in the off- 

 spring in both cases is notorious ; but some few instances of 

 botli hybrids and mongrels long retaining a imifonn character 

 could be given. The variability, however, in the successive 

 generations of mongrels is, perhaps, p^eater than in hybrids. 



This greater variability in mongrels than in hybrids docs 

 not seem at all surprising. For the parents of mongrels are 

 varieties, and mostly domestic varieties (very few ex])eriments 

 having been tried on natural varieties), and this imjjlies that 

 there lias been recent variability, Avhich would often continue 

 and be added to that arising from the act of crossing. The 

 slight variability of hybrids in the first generation, in contrast 

 with the succeeding generations, is a curious fixct, and deserves 

 attention. For it bears on the view which I have taken of one 

 of the causes of ordinary variability ; namely, that the repro- 

 ductive systeni from being eminently sensitive to changed con- 

 ditions of life, fails under these circumstances to perform its 

 proper function of producing offspring identical in all respects 

 with the parent-form. Now, hybrids in the first generation 

 are descended from sjiecies (excluding those long cultivated) 

 which have not had their reproductive systems in any way 

 allected, and they are not variable ; but hybrids themselves 

 have their reproductive systems seriously affected, and their 

 descendants are highly variable. 



Biit to return to our comparison of mongrels and hybrids : 

 Gfirtner states that mongrels are more liable than hybrids to 

 revert to cither parent-form ; but this, if it be true, is certainly 

 only a difference in degree. Mort>over, Gartner expressly states 

 that hylirids 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 dilferent obser\'ers : thus, Max Wichura doubts 

 whether hybrids ever revert to their parent-forms, and he ex- 

 perimented on uncultivated species of willows ; while Naudin, 

 on the other hand, insists in the strongest terms on the almost 

 universal tendencv to reversion in hybrids, and he experiment- 

 ed chiedy on cultivated plants. Gartner further stiites that 

 when any two species, although most closely allied to each 

 other, are crossed with a third species, the hybrids arc widely 

 different from each other; Avhereas, if two vtM-y distinct varie- 



