144 THE METHOD OF DARWIN. 



flower by its own pollen, should be prevented. 

 But he had also shown that there is a mechan- 

 ical liability to self-fertilization in the short- 

 styled form by the pollen being carried down 

 from the stamens to the pistil. These facts 

 led him to the belief that the pollen of the 

 other form is prepotent over the pollen of the 

 same form as that to which the stigma belongs, 

 when they are placed on it together. He said, 

 " There can hardly be a doubt that with hetero- 

 styled dimorphic plants, pollen from the other 

 form will obliterate the effects of the pollen 

 from the same form, even when this has been 

 placed on the stigma a considerable time before. 

 To test this belief I placed on several stigmas 

 of a long-styled cowslip plenty of pollen from 

 the same plant, and twenty hours later pollen 

 from a short -styled dark red polyanthus" (va- 

 riety of cowslip). Of the thirty seedlings, all 

 bore reddish flowers, showing that they were 

 the result of the cross. 1 



It is not surprising that, after he had verified 

 his general inference concerning prepotency in 

 heterostyled dimorphic plants by the experi- 

 ments with the highly specialized flowers of 

 the cowslip, he should take another step and 

 test the inference by a species in which there 



1 Different Forms of Flowers, etc, p. 31. 



