270 LAWS GOVERNING THE STERILITY 



•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 cross- 

 ing 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 among hybrids which are usually interme- 

 diate in structure between their parents, exceptional and 

 abnormal individuals sometimes are born, which closely re- 

 semble 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 sus- 

 ceptible to favorable and unfavorable 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, accord- 



