228 LAWS GOVERNING THE STERILITY [CHAP. IX. 



striking cases could be given. Thuret has observed the same fact 

 with certain sea-weeds or Fuci. Gartner, moreover, found that 

 this difference of facility in making reciprocal crosses is extremely 

 common in a lesser degree. He has observed it even between 

 closely related forms (as Matthiola annua and glabra) which 

 many botanists rank only as varieties. It is also a remarkable 

 fact, that hybrids raised from reciprocal crosses, though of course 

 compounded of the very same two species, the one species having 

 first been used as the father and then as the mother, though they 

 rarely differ in external characters, yet generally differ in fertility 

 in a small, and occasionally in a high degree. 



Several other singular rules could be given from Gartner: for 

 instance, some species have a remarkable power of crossing with 

 other species ; other species of the same genus have a remarkable 

 power of impressing their likeness on their hybrid offspring ; but 

 these two powers do not at all necessarily go together. There are 

 certain hybrids which, instead of having, as is usual, an inter- 

 mediate character between their two parents, always closely 

 resemble one of them; and such hybrids, though externally so 

 like one of their pure parent-species, are with rare exceptions 

 extremely sterile. So again amongst hybrids which are usually 

 intermediate in structure between their parents, exceptional and 

 abnormal individuals sometimes are born, which closely resemble 

 one of their pure parents ; and these hybrids are almost always 

 utterly sterile, even when the other hybrids raised from seed 

 from the same capsule have a considerable degree of fertility. 

 These facts show how completely the fertility of a hybrid 

 may be independent of its external resemblance to either pure 

 parent. 



Considering the several rules now given, which govern the 

 fertility of first crosses and of hybrids, we see that when forms, 

 which must be considered as good and distinct species, are united, 

 their fertility graduates from zero to perfect fertility, or even to 

 fertility under certain conditions in excess ; that their fertility, 

 besides being eminently susceptible to favourable and unfavour- 

 able conditions, is innately variable ; that it is by no means always 

 the same in degree in the first cross and in the hybrids produced 

 from this cross ; that the fertility of hybrids is not related to the 

 degree in which they resemble in external appearance either 

 parent ; and lastly, that the facility of making a first cross between 

 any two species is not always governed by their systematic affinity 

 or degree of resemblance to each other. This latter statement is 

 clearly proved by the difference in the result of reciprocal crosses 

 between the same two species, for, according as the one species or 

 the other is used as the father or the mother, there is generally 

 tome difference, and occasionally the widest possible difference, in 



