CHAP. IX.] HYBRIDS AND MONGRELS COMPARED. 243 



are more variable than hybrids ; but Gartner admits that hybrids 

 from species Avhich have long been cultivated are often variable in 

 the first generation ; and I have myself seen striking instances of 

 this fact. Gartner further admits that hybrids between very 

 closely allied species are more variable than those from very dis- 

 tinct species ; and this shows that the difference in the degree of 

 variability graduates away. When mongrels and the more fertile 

 hybrids are propagated for several generations, an extreme amount 

 of variability in the offspring in both cases is notorious ; but some 

 few instances of both hybrids and mongrels long retaining a 

 uniform character could be given. The variability, however, in 

 the successive generations of mongrels is, perhaps, greater than in 

 hybrids. 



This greater variability in mongrels than in hybrids does not 

 eeem at all surprising. For the parents of mongrels are varieties, 

 and mostly domestic varieties (very few experiments having been 

 tried on natural varieties), and this implies that there has been 

 recent variability, which would often continue and would augment 

 that arising from the act of crossing. The slight variability of 

 hybrids in the first generation, in contrast with that in the 

 succeeding generations, is a curious fact and deserves attention. 

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

 of ordinary variability; namely, that the reproductive system 

 from being eminently sensitive to changed conditions of life, fails 

 under these circumstances to perform its proper function of pro- 

 ducing 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 repro- 

 ductive 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 cf 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 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; 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 

 cultivated 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 



9* 



