OF FIRST CROSSES AND OF HYBRIDS. 287 



the cotyledons, can be crossed. Annual and perennial 

 plants, deciduous and evergreen trees, plants inhabiting 

 different stations and fitted for extremely different climates, 

 can often be crossed with ease. 



By a reciprocal cross between two species, I mean the 

 case, for instance, of a female ass being first crossed by a 

 stallion, and then a mare by a male ass; these two species 

 may then be said to have been reciprocally crossed. 

 There is often the widest possible difference in the 

 facility of making reciprocal crosses. Such cases are 

 highly important, for they prove that the capacity in 

 any two species to cross is often completely independent 

 of their sytematic affinity, that is of any difference 

 in their structure or constitution, excepting in their 

 reproductive systems. The diversity of the result in recip- 

 rocal crosses between the same two species was long ago 

 observed by Kolreuter. To give an instance: Mirabilis 

 jalapa can easily be fertilized by the pollen of M. long- 

 iflora, and the hybrids thus produced are sufficiently fer- 

 tile; but Kolreuter tried more than two hundred times, 

 during eight following years, to fertilize reciprocally M. long- 

 iflora 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 dift'er in fertility in a small, and occasionally 

 in a high degree. 



Several other singular rules could be given from Giirt- 

 ner: 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 like- 

 ness 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 



