542 



THE AMERICAN NATURALIST [Vol. LIII 



eight cases, a crossed plant, in nine cases a selfed plant, 

 flowered first. 



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 experi- 

 ments proved that 



often miu-h diniiiiisluMl or wholly (li>a}.]>oars (la, 2:270). 



This statement appears to be an ohiter dictum of Dar- 

 win's to the support of which he does not adduce direct 

 experimental evidence. 



Again he says : 



Anyhow my experiments indicate that crossing plants which have 



the most powerful of all the means for retaining some degree of dif- 

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

 later .-ionoratioMs. of the intercrossed over the self -fertilized seedlings 

 (11). 450). 



We know, he says, tliat a i>lant proi)agated for some generations in 

 hi"!, fertilization powers (ibid.). 



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

 writer knows, to be thoroughly re-investigated under com- 

 pletely controlled conditions. 



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

 that the increased vigor of intercrossed plants is due to 

 the constitution or nature of the sexual elements, which 

 condition he took to be of the general nature of differen- 

 tiation due to tlie action of environment. 



