1 90 HYBRIDISM. Chap. XIX. 



duced. Thus, as I believe, we can understand why with domes- 

 ticated animals varieties have not been produced which are 

 mutually sterile ; and why with plants only a few such cases 

 have been observed, namely, by Gartner, with certain varieties 

 of maize and verbascum, by other experimentalists with varie- 

 ties of the gourd and melon, and by Kolreuter with one kind of f 



tobacco. 



With respect to varieties which have originated in a state 

 of nature, it is almost hopeless to expect to prove by direct 

 evidence that they have been rendered mutually sterile ; for if 

 even a trace of sterility could be detected, such varieties would 

 at once be raised by almost every naturalist to the rank of 

 distinct species. If, for instance, Gartner's statement were fully 

 confirmed, that the blue and red-flowered forms of the pimpernel 

 (Anagallis arvensis) are sterile when crossed, I presume that all 



the botanists who 



grounds 



two forms are merely fleeting varieties, would at once admit 

 that they were specifically distinct. 



The real difficulty in our present subject is not, as it appears 

 to me, why domestic varieties have not become mutually in- 

 fertile when crossed, but why this has so generally occurred 

 with natural varieties as soon as they have been modified in a 

 sufficient and permanent degree to take rank as species. We 

 are far from precisely knowing the cause ; nor is this surprising, 



how profoundly ig 



sgard 



and abnormal action of the reproductive system. But we can 

 see that species, owing to their struggle for life with numerous 

 competitors, must have been exposed to more uniform conditions 

 during long periods of time, than have been domestic varieties ; 

 and this mav well make a wide difference in the result. For we 

 know 7 how commonly wild animals and plants, when taken from 

 their natural conditions and subjected to captivity 



sterile ; and the reproductive functions of organic beings which 



have always lived and been slowly modified under natural con- 

 ditions would probably in like manner be eminently sensitive to 

 the influence of an unnatural cross. Domesticated productions, 

 on the other hand, which, as shown by the mere fact of their 

 domestication, were not originally highly sensitive to changes 

 in their conditions of life, and which can now generally resist 



