FLOWERS AND INSECTS — ROSACEAE AND 
COMPOSITAE 
CHARLES ROBERTSON. 
Contributions to an account of the mutual biological rela- 
tions of the entomophilous flora and the anthophilous insect 
fauna of Macoupin County, Illinois. 
Prunus americANA L.—The trees grow a few metres 
high and are covered in early spring with a profusion of white 
flowers, which appear with the leaves. The corolla expands 
from 15 to 20mm. When the corolla opens, the style with 
its stigma already receptive is exposed to insects, while the 
anthers are still closed. This gives abundant opportunity for 
cross-pollination between flowers of the same or of different 
trees. After the anthers begin to dehisce, cross-pollination 
is still readily effected by insects touching the stigma first. 
But insects coming without pollen may effect self-pollination. 
In case insect-visits fail, spontaneous self-pollination may 
occur in those flowers in which some of the stamens equal or 
exceed the style in length, by the flowers closing up so that 
‘the anthers may be thrown against the stigma, or turning 
horizontally, so that some of the pollen may fall upon the 
stigma. In many flowers, however, the stigma so far sur- 
passes the anthers that spontaneous self-pollination is impos- 
sible. Nectar is secreted by the broad wall of the receptacular 
tube. The tube is somewhat contracted at the mouth and 
slightly obstructed by the bases of the filaments. 
The flowers are in bloom from April 15 to May 5. They 
are visited mainly by bees and flies. The following visitors 
were noted on April 17, 26 and 27: — 
__ Hymenoptera — Apidae: (1) Apis mellifica L. $s. and c. p., ab.; Andren- 
idae: (2) Andrena sayi Rob. jf’ Q,s.and c. p., freq.; (3) A. salicis Rob. B85 
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