Chap. IX.] OF FIRST CROSSES AND OF HYBRIDS. 15 



their reproductive systems. The diversity of the result 

 in reciprocal crosses between the same tw^o 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 suffi- 

 ciently fertile; but Kolreuter tried more than two hun- 

 dred times, during eight following years, to fertilise 

 reciprocally M. longiflora with the pollen of M. jalapa, 

 and utterly failed. S&veral 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 recipro- 

 cal crosses is extremely common in a lesser degree. He 

 has observed it even between closely related forms (as 

 Matthiola annua and gilabra) 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 spe- 

 cies having first been used as the father and then as 

 the mother, though they rarely differ in external char- 

 acters, yet generally differ in fertility in a small, and oc- 

 casionally 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 



