228 STUDY OF COMMON PLANTS. 



XXXIV. THE MILKWEED FAMILY. 

 ASCLEPIADACE^. 



MATERIAL REQUIRED. 



Flowers of Asclepias Cornuti, Decaisne. Alcoholic specimens will 

 serve if fresh ones are not to be had, but there is an advantage 

 in having a supply of both. 



MILKWEED. Asclepias Cornuti, Decaisne. 

 Flowers. 



Our study of the milkweed will be restricted to the 

 flowers, which present an extraordinary mechanism for 

 securing cross-fertilization through the agency of insects. 

 They are borne in a -conspicuous umbel and attract numer- 

 ous visitors, particularly bees, wasps, and flies. Both the 

 odor and color are attractive, and there is an abundant 

 supply of nectar. The plant is absolutely dependent on 

 insects for fertilization. 



Observe first the form and position of the floral envel- 

 opes. They are reflexed and covered on their lower 

 surface with short, woolly hairs. (This is contrary to 

 the general rule noticed by Kerner, Flowers and their Un- 

 bidden Cruests, that plants protected by milky juice have 

 smooth leaves, and are without any other appliances for 

 the protection of their flowers from crawling animals.) 



The crown is the most conspicuous part of the flower. 

 It consists of five hollow bodies, cuculli, each of which has 

 an incurved horn projecting from its opening. 



