REPRODUCTION AND HEREDITY 317 



plasm a corresponding independent rudiment (Anlage) : that 

 during crossing and fertilization these ' rudiments ' together 

 form in the egg-cell a pair ; and that finally during the further 

 development the characteristic feature of one 'parent' conceals 

 that of the other. The prevalent character is usually described 

 as the ' dominant,' the other as the ' recessive ' character, and 

 the phenomenon itself as the 'rule of prevalence.' 'If,' says 

 Correns, ' the phylogenetic condition of both parents can be 

 determined it is almost always clear that the phylogenetically 

 higher character, i.e., the younger ' rudiment,' dominates. 



But this ' rule of prevalence ' finds no universal application, 

 for there are numerous cases in which the hybrids of the first 

 generation represent a mixed form and exhibit the characters 

 of their parents jointly. These two extremes are then connected 

 by every conceivable transition form. The following is an in- 

 stance of the second case. Every one knows the beautiful 

 Mirabilis Jalapa, for its large red, white, yellow, or variegated 

 flowers has made it a favourite garden flower. If we cross a 

 red-flowering with a white-flowering form, the hybrid shows 

 flowers of a light pink shade. If we now breed from these 

 hybrids under strict self-fertilization "we shall again observe a 

 remarkable ' Mendelian split,' but this time in somewhat different 

 proportions. The second hybrid generation supplies three dif- 

 ferent kinds of individuals, half of all descendants showing the 

 intermediate light pink type, 25 per cent, the red, and 25 per 

 cent, the white type. But while the intermediate hybrids con- 

 tinue to l mendel,' i.e., to produce 50 per cent, of differentiated 

 descendants, the hybrids which had reverted to the form of their 

 ' grandparents ' prove themselves perfectly constant. This case 

 illustrates Mendel's rule far more clearly than the instance of 

 pea and nettle, because here the ' splitting' is not obscured by 

 the ' domination ' of one character. Is it not strange that when 

 in the crossing of two varieties, differing only in one point, the 

 character of one parent is completely lost in the hybrid genera- 

 tion, or that, as in the Mirabilis Jalapa, only intermediate hybrids 

 originate, in the second generations the characters which were 

 apparently extinct, or at least intermixed, suddenly reappear pure 

 and in fixed proportions ? Can cell-investigations or speculation 

 offer a satisfactory explanation of this phenomenon ? 



