Chap. IX.] OF FIEST CKOSSES AND OF HYBEIDS. 15 



in their reproductive systems. The diversity of the 

 result in reciprocal crosses between the same two 

 species was long ago observed by Kolreuter. To give 

 an instance: Mirabilis jalapa can easily be fertilised 

 by the pollen of M. longiflora, and the hybrids thus 

 produced are sufficiently fertile ; but Kolreuter tried 

 more than two hundred times, during eight following 

 years, to fertilise reciprocally M. longiflora with the 

 pollen of M. jalapa, and utterly failed. Several other 

 equally 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 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 



