Chap. XVI. THE CROSSING OF VARIETIES. 101 



almost certainly have been observed. In investigating the 

 fertility of crossed varieties many sources of doubt occur. 

 Whenever the least trace of sterility between two plants, 

 however closely allied, was observed by Kolreuter, and more 

 especially by Gartner, who counted the exact number of seed 

 in each capsule, the two forms were at once ranked as dis- 

 tinct species; and if this rule be followed, assuredly it will 

 never be proved that varieties when crossed are in any degree 

 sterile. We have formerly seen that certain breeds of dogs do 

 not readily pair together ; but no observations have been made 

 whether, when paired, they produce the full number of young, 

 and whether the latter are perfectly fertile inter se ; but, sup- 

 posing that some degree of sterility were found to exist, 

 naturalists would simply infer that these breeds were descended 

 from aboriginally distinct species; and it would be scarcely 

 possible to ascertain whether or not this explanation was the 

 true one. 



The Sebright Bantam is much less prolific than any other 

 breed of fowls, and is descended from a cross between two very 

 distinct breeds, recrossed by a third sub-variety. But it would 

 be extremely rash to infer that the loss of fertility was in any 

 manner connected with its crossed origin, for it may with more 

 probability be attributed either to long-continued close inter- 

 breeding, or to an innate tendency to sterility correlated with 

 the absence of hackles and sickle tail-feathers. 



Before giving the few recorded cases of forms, which must be 

 ranked as varieties, being in some degree sterile when crossed, 

 I may remark that other causes sometimes interfere with 

 varieties freely intercrossing. Thus they may differ too greatly 

 in size, as with some kinds of dogs and fowls : for instance, 

 the editor of the ' Journal of Horticulture, &c.,' 2 says that 

 he can keep Bantams with the larger breeds without much 

 danger of their crossing, but not with the smaller breeds, such 

 as Games, Hamburgs, &c. With plants a difference in the 

 period of flowering serves to keep varieties distinct, as with the 

 various kinds of maize and wheat: thus Colonel Le Couteur 3 

 remarks, "the Talavera wheat, from flowering much earlier than 

 any other kind, is sure to continue pure." In different parts of 



2 Dec. 18G3, p. 484. 3 0n the y ar i eties f Wheat, p. QQ. 



