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IOWA ACADEMY OF SCIENCES 
not visible, but when the pollen is shed it is distinctly 
visible. The stigma contains the small papillae along the 
sides. The nectar in some of the species rises up to the 
throats of the flowers and numerous insects are therefore 
attracted to these flowers. In some of the species the pro- 
boscis of insects need only be one to one and a half milli- 
meters long to reach the bottom of the throat of the 
corolla. Mueller says: 
So that the rich store of honeys is accessible not only to bees and Lepi- 
doptera, but to wasps, flies and beetles, which seek it diligently. 
Bat if insects do not visit the flower until the stigmatic edges of the 
branches of the style have already bent outwards, then self-fertilization is 
possible, since in this case the hairs of the style still remain covered with 
pollen. If insects do not visit the flower at all, some of the pollen grains, 
which hang in little clumps to the hairs, may easily fall of themselves upon 
the stigmatic papillae. In tine weather, and in the open air, this can scarcely 
ever take place, for Cnicus arvensis is one of the most abundantly visited of 
all our native plants. As the following list shows, very few insects resort 
to it for the sake of its pollen, but very many for its honey. 
In regard to the pollinators, the writer has observed 
many different kinds of bees in Iowa. The bumblebees 
thrust their proboscis into the long tubular flowers, and 
so eager are they to get the nectar, that they are easily 
caught. 
Mr. Weed says: 
Megachile is a frequent visitor, collecting in great quantity the abundant 
pollen on her abdominal brushes. The beautiful steel blue or green bees 
of the genus Agapostemon are common, and various smaller species often 
occur. The two-winged flies of the order Diptera rank next to the Hymen- 
optera in frequency of visits, although perhaps the butterflies are equally 
numerous. 
Lepidoptera are also common. Of the Lepidoptera, 
attention may be called to the Colias philodice , as well as 
Pier is, Dana is archippus and Papilio turnus. And Mr. 
Weed notes as follows concerning the pollinators: 
The list of visitors to the common Thistle is an extended one. In con- 
spicuousness, if not also in frequency of visits, the bumblebees take the 
lead among the Hymenoptera . But they are not the large and handsome 
bees found on the Arbutus in May; they are much smaller in size and less 
attractive in appearance. This difference is explained by a glance at the 
life-histories of the bumblebees. The large specimens which appear in 
spring are the hibernating females or queens, which have passed the winter 
snugly ensconced in last year’s nests, or some sheltered situation. 
