246 EXPERIMENTAL EVOLUTION LECT. 



instance among a thousand. Why, and how it is that 

 some individuals are thus endowed, we know not. It 

 must be noticed that the pre-eminence of one of the 

 progenitors, as a race or variety is not constant ; while 

 variety a for instance, possesses stronger hereditary 

 tendencies when crossed with b and r, its tendencies 

 are overpowered by those of d in a crossing with this 

 variety ; and in order to ascertain exactly or more 

 accurately the relative energy of these tendencies, many 

 systematic crossings would have to be made. This 

 pre-eminence of one of the progenitors over the other, 

 in regard to the character of the progeny may in some 

 cases be so considerable that no difference is apparent ; 

 it would seem that no crossing has been made and 

 that both progenitors belong to the same variety. 1 

 As M. C. Dareste 2 rightly observes, " in the present 



1 It may happen, however, that the difference, as concerns external 

 characters, is well marked, but then one marked physiological feature 

 may be transmitted from one of the progenitors to the hybrid ; for 

 instance, M. Millardet, in his Essai sur F Hybridation de la Vigne 

 (Paris, Masson, 1891), shows that in some hybrids between two varieties 

 oi grape-vine, the marked immunity of one of the progenitors the 

 male especially towards phylloxera, is transferred to the progeny, 

 notwithstanding the reverse tendency in the other progenitor. The 

 same writer notices that when the American variety is used as male, 

 immunity towards phylloxera is considerable, while the amount of 

 fruit produced is smaller ; the reverse obtains when the American 

 variety is used as female. Similar facts have been observed by Th. 

 Niebnei, Die Rose, Berlin, 1880. 



2 Noiivdle Exposition d'un Plan d' Experiences sur la Variabilite 

 des Aniiiiaux, p. 16 (Bull. Soc. Zool. Acclimatation, 1888). 



