222 IOWA ACADEMY OF SCIENCES 



not visible, bat 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, bat to wasps, flies and beetles, which seek it diligently. 



But 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 lovy^a. . 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. 



Lepid optera are also common. Of the Lepidoptera^ 

 attention may be called to the CoJias philodire, as well as 

 Pier is, Dana is arcJiippus 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. 



