218 IOWA ACADEMY OF SCIENCES 



Fig. II. Leaf and bracts of Cnicus loivensis 

 3, outer bracts showing tiie 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 proterandi'ous. 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. 

 lowensis and C. (tlfissiutHs and ('. discolar are sensitive. 

 By placing a brush or a lead pencil on the anthers they 



