232 ON THE ORIGIN OF SPECIES 



reciprocal crosses between the same two species waa 

 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 re- 

 ciprocal crosses is extremely common in a lesser degree. 

 He has observed it even between forms so closely 

 related (as Matthiola annua and glabra) that many 

 botanists rank them 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, 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 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. 



