80 



in Asclepias verticillata the pollinia are usually attached 

 to hairs of insects. In A^^clepias cornuti the pollinia are 

 more frequently attached to the claws, It is dangerous for 

 small insects to extract the pollinia and insert them into the 

 siigmatic chamber. In one day Mr. Robertson picked 

 thirty-four dead hive bees from flowers. The feet become 

 entiingled with the pollen masses. In another species, A, 

 snllivantii, he states that in a small patch bearing fifty-two 

 follicles one hundred and forty-seven dead bees were found. 

 In a single umbel he has often found four, and in one case 

 seven dead hive-bees. The insects pollinating these flowers 

 belong to the bees {Hymenoptera)^ butterflies and moths 

 {Lepidoptera), flies {Diptera). a few Coleoptera and 

 Hemiptera. Some of these visitors are useless since they 

 do not light on the flower. Others cannot extract the 

 pollinia. Humming birds have been observed, but Mr. 

 Robertson thinks ihey are useless. 



The Gentians are among the prettiest of 



Geutiaaaceae. ^^^^ autumn flowers. Most of the species 



in (Central Iowa have blue flowers, G. Quinquefolia L., 



and Q. Andrewsii, Griseb. but G. flavida, Gray has white 



flowers. 



The G. AndreiosiiGriseh., which we may take as a 

 type, grows in clumps in marshes and has a blue corolla 

 which is closed at the mouth, with toothed appendages. 

 'I he flowers are proterandrous. Tlie stamens are united 

 with the corolla tube and the free ends occur over the pistil. 

 Bumble bees in search of nectar must possess a tongue 15-16 

 mm. long, which must be thrust between the filaments^ In 

 speaking of the protection, Mr. Robertson says: 



"There is no doubt that flow^ers were originally of such a 

 form that almost any insect could enter them and reach the 

 nectar. Many have narrowed the entrance by the develop- 



