Chap. Till. LAWS OF STERILITY. 259 



Gartner : for instance, some species ha Ye 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 intermediate 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, ex- 

 ceptional 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 fertility in the hybrid is 

 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 unfavourable 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 exter- 

 nal 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 



