IOWA ACADEMY OF SCIENCES. 
83 
insects found on one of the wild plums, and found that the 
wild bees ranked first in importance. A few Diptera visit 
the flowers but are of little importance. Waugh (24) 
gives a list of eighteen Hymenoptera and ten Diptera taken 
from plum blossoms at Denton, Md., Ithaca, N. Y., 
Madison, Wis., and Burlington, Yt. This list includes the 
Apis mellifica , Linn., several species of Bombus and eight 
species of Andrena. The honey bee is of the greatest 
importance in all cases, though several of the species of 
Andrena are very active. In another connection Waugh (28) 
gives a list of seven Hymenoptera and nine Diptera 
taken in Oklahoma, Maryland, Iowa and Vermont. Very 
few species are identical in the two lists, showing the 
honey bee to be probably the one universal pollinator. 
Collections made in the spring of 1899 at Ames were found 
to contain the following species: 
Hymenoptera. Apis mellifica Linn.; Bombus Virgmicus 
Oliv.; Andrena bipunctata Cr. Diptera. Phobia fusciceps. 
The honey bees outnumbered all the other species 
ten to one. The humble bees are too scarce at this season 
to be of importance. 
The flower of the plum secretes a large amount of nectar 
and this proves very attractive to the bees. In the majority 
of the trees the anthers and the stigmas are about on a 
level. The honey bee on alighting on the flower clings to 
the stamens, covering the underside of its body with the 
pollen. This is brushed off upon the stigma of the same or 
other flowers. There is a very marked difference in the 
methods used by the ordinary honey bee and the smaller 
bees as the Andrenas in getting at the nectar. The former 
forces its way into the calyx cup from above, while the 
latter sips from the edge of the cup, working its way in 
among the bases of the stamens. They are thus almost 
useless as pollinators as they rarely come in contact with 
the anthers. 
In most flowers there are no special external structural 
adaptations to insure cross pollination, the plant seeming 
to rely very largely on self sterility to effect a cross. This 
view is not held by Heideman (15) who finds in the plum 
