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IOWA ACADEMY OF SCIENCES 
Fig. ii. Leaf and bracts of Cnicus Iowensis 
3, outer bracts showing the dorsal glutinous ridge and stout spines; 4 , the inner long bracts. 
Diptera are held fast. The writer has observed ants and 
several different kinds of Diptera on these glands. 
Pollination. — Several of the species have been studied 
in detail. Below will be found some of the references. f 
* All of the thistles bear conspicuous heads. The heads 
are many flowered and very attractive. Each flower con- 
sists of a long tubular corolla with a spreading limb. The 
tube is very much contracted. The anthers are united 
into a tube, the lower portion being usually sagitiate. The 
pollen grains of all the species are very spiny, and owing 
to this fact they adhere readily to the insect’s body. The 
filaments are frequently hairy, or in some cases somewhat 
pilose. The flowers are strongly proterandrous. In the 
first stage a large quantity of pollen is pushed out by the 
style through the opening of the anthers. This is accom- 
plished by the small brush hairs which occur at the joint 
on the style. In some few cases, however, these hairs are 
very much reduced. These hairs not only help to push 
the pollen out, but it prevents it from falling to the bot- 
tom of the corolla tube. The stamens, especially in C. 
Iowensis and C. altissimus and C. discolar are sensitive. 
By placing a brush or a lead pencil on the anthers they 
