IOWA ACADEMY OF SCIENCES. 
81 
This conclusion is reached by Speer (:8) in regard to the 
Minor plum, which failed to fruit at Ames for him, though 
fruiting abundantly farther south. Goff also holds this 
opinion, but Waugh (22) declares that this is not tenable,, 
as, with the exception of one location which had a uni- 
formly high percentage of defective pistils, he found that 
the percentage of defective pistils decreased rather than 
increased northward. Craig (7) gives the percentage of 
fruit buds injured during the winter of ’98-99 in Iowa, and 
finds them to vary from 0 per cent to 100 per cent in dif- 
ferent varieties and localities. Goff (10) kept records of the 
variations in temperature during several winters, and 
studied the effect of variations in temperature on the buds. 
He comes to the conclusion that very often cold weather 
does much damage. Lord {16) goes so far as to claim that 
the abortion of pistils in the plum is caused entirely by 
unfavorable climates. 
During the latter part of March or the first of April 
growth is resumed in the flower. Should a cold period 
intervene at this time it is undoubtedly true that a large 
share of the pistils are killed or rendered abortive. The 
pollen mother cells separate, and by the middle of April 
the buds are noticeably swollen, the anthers increase rapidly 
in size, as do the pistils and the ovules. Early in May the 
blossom opens. The flower varies much in different varie- 
ties. The single pistil is one celled and bears two ovules. 
There are usually about twenty stamens arranged in a 
double ring. The dehiscence furnishes an abundance of 
pollen. In the normal flowers of most of the varieties cul- 
tivated at Ames the pistils and the stamens are about the 
same height. In several forms, notably the Wyant, the 
inner row of stamens opened first, sometimes preceding 
the outer stamens by a day or more. Pollination normally 
takes place almost immediately and the pistil ceases to be 
receptive. Pollination is brought about almost entirely by 
the common honey bee (Apis mellifica Linn). Much has been? 
written concerning the adaptations of Prunus for cross- 
pollination. 
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