228 PLANT HYBRIDIZATION BEFORE MENDEL 



Darwin broached the view that the increased vigor of first 

 generation hybrids was chiefly due to the forms used in the cross 

 having been exposed to somewhat different conditions of life. He 

 also contended that his experiments proved that: 



"if all the individuals of the same variety can be subjected during 

 several generations to the same conditions, the good derived from cross- 

 ing is often much diminished or wholly disappears." (la, 2:270.) 



This statement appears to be an obiter dictum of Darwin's, to 

 the support of which he does not adduce direct experimental evi- 

 dence. 



Again he says : 



"Anyhow my experiments indicate that crossing plants, which have 

 been long subjected to almost though not quite the same conditions, 

 is the most powerful of all the means for retaining some degree of 

 differentiation in the sexual elements, as shown by the superiority in the 

 later generations of the intercrossed over the self-fertilized seedlings." 



(lb, pp. 454-5-) 



"We know," he says, "that a plant propagated for some generations in 

 another garden in the same district serves as a first stock, and has high 

 fertilizing powers." {ib., p. 455.) 



The importance of this view has yet, so far as the writer 

 knows, to be re-investigated under controlled conditions. 



It was Darwin's view, as the result of his experiments, that 

 the increased vigor of intercrossed plants is due to the constitu- 

 tion or nature of the sexual elements, which conditions he took 

 to be of the general nature of differentiation due to the action of 

 environment. 



"It is certain," he says, "that the differences are not of an external 

 nature, for two plants which resemble each other as closely as the in- 

 dividuals of the same species ever do, profit in the plainest manner when 

 intercrossed, if their progenitors have been exposed during several gen- 

 erations to different conditions." (lb, p. 270.) 



Darwin asserts that there is not a single case in his experi- 

 ments 



". . . which affords decisive evidence against the rule that a cross be- 

 tween plants, the progenitors of which have been subjected to some- 

 what diversified conditions, is beneficial to the offspring." {ib., p. 281.) 



The fact that increased vegetative vigor In first generation hy- 

 brids was also sometimes accompanied by diminished fertility 

 was likewise observed by Darwin. 



"For it deserves especial attention that mongrel animals and plants. 



