82 
IOWA ACADEMY OF SCIENCES. 
The time of blossoming, that is, the period of fall bloom, 
for the tree usually lasts from three to five days, or even lon- 
ger in unfavorable seasons when pollination does not sooner 
occur. Many of the experiment stations have determined 
the blossoming periods of the various plums at different 
places, Goff in Wisconsin, Waugh in Vermont, Craig in 
Iowa and others. These tables reveal that there is a suc- 
cession of blooms in different varieties for several weeks. 
The stigma of the pistil becomes receptive, that is, covered 
with a sticky secretion within a short time after the open- 
ing of the flower. If the weather is favorable, pollination 
occurs within a few hours or even minutes. Any one who 
has stood near a plum tree on a bright day with the tree 
in full bloom will realize that with such a buzzing, 
humming host of insects as are present there is little 
chance that the flower will remain for a long time unpol- 
linated. The insects that occur upon the flowers have 
been collected and named at several stations in the United 
States. 
Robertson (28) gives the following list of insects found 
pollinating the plum in Illinois: Hymenoptera; Apidje; 
Apis mellifica L.; Andrenid^e. Andrena sayi Rob.; A . 
salicis Rob.; A. cressonii Rob.; A. flavoclypeata Sm. ; 
Halictus lerouxii Lep.; H. zephyrus Sm.; If. confusus Sm.; 
H. Stultus Cr.; Colletes incequalis Say. Diptera. Bom- 
bylid^e. Bomby lins major L.; Syrphid^e. Chrysogaster 
nitida Wd.; C. ustulata L.; Platychirus hyperboreus Staeg.; 
Syrphus americanus Wd.; S. ribesii L.; Mesograpta gemi- 
nata Say.; Sphoerophoria cylindrica Sav.; Eristalis dimidi- 
atus Wd.; Helophilus similis Mcq.; Br achy palpus fr onto sus 
Lw.; Tachnid^e. Gonia frontosa Say.; Muscid^e. Lucilia 
ccesar L.; L. cornicina F.; Cordyluridje. Seatophaga 
squalida Mg.: Lepidoptera. Nymph alid^e. Pyrameis 
atalanta L.; P. huntera F.; Noctuid^e Plitsia simplex Gn. 
Coleoptera; Chrysomelid^e. Orsodachnaatia Ahr. 
Vestal and Garcia (6> found that at the New Mexico 
Station the honey bee ranked first in abundance and 
importance as a pollinator, closely followed by the wild 
bees. Cockerell (6) in the same territory studied the 
