THE PLUM IN KANSAS. 97 



we may infer with mucli safety that the species is heterostyled." If 

 the above test is correct, then a few individuals of our species are 

 heterostyled, and many more are tending in that direction. Bisexu- 

 ality is clearly defined in many individuals in nature, the male form 

 being more numerous. I have frequently met forms entirely devoid 

 of pistils. Now and then I have found forms which do not appear to 

 come under any division of the foregoing classification. For instance, 

 I have a tree which for three years has produced flowers, each of 

 which had two, and in a few instances three apj^arently perfectly de- 

 veloped pistils. So far no fruit has set, although I made last spring 

 a number of hand crosses to determine its affinity. These freak 

 forms are the exception, and with them this paper has nothing to do. 



POLLINATION AND FERTILIZATION. 



The fruit-buds of P. amerlcana are developed on the spurs and 

 spur-like branches of the current season's growth. The following 

 spring, on approach of steady warm weather in May, the buds swell 

 and expose from one to five flowers, in a simple, umbel-like cluster. 

 The period of bloom and the time when pollinatian may be efPected 

 generally extends over two or three days, and in cool and cloudy 

 weather it may extend over a week. Pollination is effected by the 

 aid of wind or insects. Within from two to twenty-four hours after 

 the blossom has fully expanded, or, in the dichogamous forms, after 

 the pistil and stigma have been exposed to light and warmth, the 

 stigma becomes receptive, as may be plainly seen with a glass of 

 moderate diameters by the glistening secretion on the stigma. Pollen 

 ripens, during clear, warm weather in about the same time, varying 

 slightly in the different varieties. Within three or four days after 

 fertilization has been effected the petals drop off, and the calyx tube 

 is parted over the now slowly swelling ovary and drops off. When 

 pollination has not been effected the blossom continues fresh for sev- 

 eral days, although the stigma may have become covered with dust 

 and withered and become non-receptive, and it finally drops off, the 

 peduncle remaining for a day or so longer. The peduncle lengthens 

 to nearly its full length from the time the blossom bursts from the 

 bud until fertilization is complete, and when legitimately fertilized 

 enlarges in diameter. When fertilization has been illegitimately ef- 

 fected the peduncle does not enlarge in diameter as much, and the 

 slightly enlarged ovary usually falls, together with the peduncle, within 

 from three to twenty days after fertilization. 



The season of full bloom ranges in different varieties over a period 



of about ten days. The past season, my earliest-blooming varieties 



were in full bloom May 2, and the latest May 10. The actual time in 



the life of a blossom during which fertilization may be effected 



—7 



