140 THE GENESIS OF SPECIES [Chap. 



closely allied species are almost invariably in some de- 

 gree sterile." 



Again, after speaking of " the general law of good being 

 derived from tlic intercrossing of distinct individuals of 

 the same species," and of the evidence that the pollen of 

 a distinct variety or race is prepotent over a tiower's own 

 pollen, ^Ir. Darwin adds the very significant remark : ^ 

 " When distinct specks are crossed, tlie case is directly 

 the reverse, for a plant's own pollen is almost always \)Yii- 

 potent over foreign pollen." 



Again he savs : - " I believe from observations commiini- 

 cated to me by ^Mr. Hewitt, who has had great experience 

 ill hybridizing pheasants and fowls, that the early death of 

 the embiyo is a very frequent cause of sterility in first 

 crosses. Mr. Salter has recently given the results of an 

 examination of about oOO eggs produced from various 

 crosses between three species of Gallus and their hybiids. 

 The majority of these eggs had been fertilized, and in the 

 majority of the fertilized eggs the embryos either had been 

 partially developed and had then aborted, or liad become 

 nearly mature, but the young chickens had been unable 

 to break throu«di the shell. Of the chickens which were 

 born, more than four-hfths died within the first few days, 

 or at latest weeks, ' without any obvious cause, apparently 

 from mere inability to live,' so that from 500 eggs only 

 twelve chickens were reared. The early death of hybrid 

 embryos probably occurs in like manner with plants ; at 

 least it is known that hybrids raised from very distinct 

 species are sometimes weak and dwarfed, and perish at an 

 early age, of which fact ^lax Wichura has recently given 

 some striking cases with hybrid willows." 



1 "Oriyiu of species," 5th edition, 1S69, p. 115. ^ ii^jj. p, 323. 



