34 The Problems 



principles do not apply. These are the phenomena upon 

 which Mendel touches in his brief paper on Hieracium. 

 As he there states, the hybrids, if they are fertile at all, 

 produce offspring like themselves, not like their parents. 

 In further illustration of this phenomenon he cites Wichura's 

 Salix hybrids. Perhaps some dozen other such illustrations 

 could be given which rest on good evidence. To these 

 cases the Mendeliau principle will in nowise apply, nor is it 

 easy to conceive any modification of the law of ancestral 

 heredity which can express them. There the matter at 

 present rests. Among these cases, however, we perceive 

 several more or less common features. They are often, 

 though not always, hybrids between forms differing in 

 many characters. The first cross frequently is not the 

 exact intermediate between the two parental types, but 

 may as in the few Hieracium cases be irregular in this 

 respect. There is often some degree of sterility. In the 

 absence of fuller and statistical knowledge of such cases 

 further discussion is impossible. 



Another class of cases, untouched by any hypothesis of 

 heredity yet propounded, is that of the false hybrids of 

 Millardet, where we have fertilisation without transmission 

 of one or several parental characters. In these not only 

 does the first cross show, in some respect, the character or 

 characters of one parent only, but in its posterity no re- 

 appearance of the lost character or characters is observed. 

 The nature of such cases is still quite obscure, but we have 

 to suppose that the allelomorph of one gamete only developes 

 after fertilisation to the exclusion of the corresponding alle- 

 lomorph of the other gamete, much if the crudity of the 

 comparison may be pardoned as occurs on the female side 

 in parthenogenesis without fertilisation at all. 



