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THE AMERICAN NATURALIST [Vol. LIII 



They differed also to a wonderful degree in constitutional vigor. The 

 crossed plants flowered first, and produced twice as many flower-stems; 

 and they afterward increased by stolons to such an extent as almost 

 to overwhelm the self -fertilized plants (lb, 302). 



Darwin holds that the inferiority of the selfed seed- 

 lings in height can have been in no way due to any mor- 

 bidity or disease in the mother plants ; certainly, he main- 

 tains, no such theory of a diseased condition would in any 

 wise hold, in the case of 



conditions (lb, 445). 



In four out of the five cases experimented with, the in- 

 tercrossing of flowers upon the same plant did not differ 

 in effect from' tlie strictest self-fertilization. Conclud- 

 ing, he says : 



On the whole the results here arrived at . . . agree well with our 

 general conclusion, that the advantaire of a cross depends on the 



Darwin's ex])eriments indicated as in the case of 

 heartsease and sweet pea, that 



the advantage derived from a cross ])etween two plants was not con- 

 fined to the offspring of the first generation (lb, 305). 



Laxton's varieties of sweet peas produced bv crossing, 

 as Darwin says: 



