APRIL, 1906. 
SOME NOTES ON THE POLLINATION OF FLOWERS. 
15 
sayi Rob. female, searching for honey; (3) Ceratina dupla Say 
female, c. p.; (4) Zadontomerus tcjonensis Cr. male, searching 
lor honey; Andrenidae. : (5) Andrena vicina Sm. male, female in 
cop., female, c. p. ; (6) A. milwaukeensis Graen. female, c. p. ; (7) 
Halictus lerouxii Lep. female, c. p.; (8) H. neuroticus Vach. 
female, c. p. ; (9) H. zephynis Sm. female, c. p. ; ( 10) H. sparsus 
Rob. female, c. p. 
B. FLIES. 
Bombyliidae: (11) Bombylius major L., probing around the 
bases of the filaments for nectar ; Syrphidae : (12) Syrphus amer- 
icanus Wied., f. p.; (13) Mcsogramma marginata Say, f. p.; 
(14) Crioprora cyanogaster Loew, f. p. 
c. BUTTERFLIES. 
Rhopalocera: (15) Pontia rapae L., I specimen alighting on 
the flower. An exceptional visitor. 
In Southern Illinois the honey-bees visit these flowers in such 
numbers as to drive the other visitors away, and for this reason 
Robertson was not able to observe more than 3 bees (Halictus), 
1 Syrphid-fly, and 1 beetle, at the flowers. He considers bees of 
the genera Andrena and Halictus, and flies of the family Syrphidae 
as the normal visitors. Our observations around Milwaukee 
support his views. In our neighborhood the honey-bee is not of 
so frequent occurrence as to interfere to any extent with the 
native visitors of our flowers. 
The flowers of JefTersonia, as also of Sanguinaria appear 
before the green leaves of these plants are fully developed, and 
before the leaves of the surrounding plants have become visible. 
For this reason the large white flowers stand out very prominently 
against the background of the woodlands in early spring. They 
are in competition with each other for the attention of the same 
set of visitors, mainly Andrenidae and Syrphidae, and to these 
they offer pollen only. Wherever these flowers occur in sufficient 
numbers to be attractive to those insects they undoubtedly 
succeed in obtaining cross-pollination for the majority. If in 
JefTersonia insects fail to effect cross-pollination or at least self- 
pollination on the first day, then the flower closing for the night 
insures spontaneous self-pollination by the aid of a characteristic 
contrivance. In Sanguinaria spontaneous self-pollination is not 
brought about so early, it is resorted to rather late after the 
visitors have had ample time to transport pollen to the stigma. 
