90 ON THE INTERCROSSINO 



pair for each birth. Modern research has much diminished 

 the number of supposed hermaphrodites and of real herma- 

 phrodites a large number pair; that is, two individuals regu- 

 larly unite for reproduction, which is all that concerns us. 

 But still there are many hermaphrodite animals which cer- 

 tainly do not habitually pair, and a vast majority of plants 

 are hermaphrodites. What reason, it may be asked, is 

 there for sujDposingin these cases that two individuals ever 

 concur in reproduction? As it is impossible here to enter 

 on details, I must trust to some general considerations 

 alone. 



In the first place, I have collected so large a body of 

 facts, and made so many experiments, showing, in accord- 

 ance with the almost universal belief of breeders, that with 

 animals and plants a cross between different varieties, or 

 between individuals of the same variety but of another 

 strain, gives vigor and fertility to the offspring; and on 

 the other hand, that close interbreeding diminishes vigor 

 and fertility; that these facts alone incline me to believe 

 that it is a general law of nature that no organic being 

 fertilizes itself for a perpetuity of generations; but that a 

 cross with another individual is occasionally — perhaps at 

 long intervals of time — indispensable. 



On the belief that this is a law of nature, we can, I 

 think, understand several large classes of facts, such as 

 the following, which on any other view are inexplicable. 

 Every hybridizer knows how unfavorable exposure to wet 

 is to the fertilization of a flower, yet what a multitude of 

 flowers have their anthers and stigmas fully exposed to the 

 weather! If an occasional cross be indispensable, notwith- 

 standing that the plant's own anthers and pistil stand so 

 near each other as almost to insure self-fertilization, the 

 fullest freedom for the entrance of pollen from another in- 

 dividual will explain the above state of exposure of the 

 organs. Many flowers, on the other hand, have their 

 organs of fructification closely inclosed, as in the great 

 papilionaceous or pea-family; but these almost invariably 

 present beautiful and curious adajDtations in relation to the 

 visits of insects. So necessary are the visits of bees to 

 many papilionaceous flowers, that their fertility is greatly 

 diminished if these visits be prevented. JMow, it is scarcely 

 possible for insects to fly from flower to flower, and not to 



