MILKWEED FAMILY ASCLEPI ADACEAE 



The Milkweed family consists of about 2,000 widely distrib- 

 uted species, most of which are found in the tropics and 

 warmer temperate regions. 



As a whole, the family is characterized by paired leaves, 

 copious milky juice or latex, and curiously shaped flowers. It 

 furnishes some minor drugs, one or two notorious weeds such 

 as the Common Milkweed and the Anglepod, and in young 

 shoots of the foriner possible asparaguslike food for human 

 beings. The latex contains the hydrocarbons that form rubber, 

 which has been produced experimentally from some species. 



Some of the flowers are beautiful and delightfully fragrant, 

 and others are ill smelling, but all have practically the same 

 highly specialized foim for insect pollination. The formation, 

 however, is not to insure self-pollination, as stigma and anthers 

 do not ripen together, but is to compel visiting insects to gather 

 pollen in the act of sipping nectar from the flower. From the 

 base of the corolla grows a corollalike structure called the 

 crown. The 5 lobes of the crown are united at the base, usually 

 into a short column or collar whose height varies with the spe- 

 cies, and bear at varying heights along their inner surface 

 spurs which may or may not be included in the crown. The 

 lobes are usually called hoods and the spurs are referred to as 

 horns. The whole structure surrounds the stamens and forces 

 the anthers to touch in a circle around the pistil. In most cases 

 the filaments are united into a column. Sepals and petals are 

 reflexed in full bloom. 



Insert a pin into one of the slits in the crown, with the 

 point inward toward the anthers. Pull upward and you will 

 find 2 pollen masses adhering to the pin. Now the bee, when it 

 comes in search of nectar, alights on the adequate surface of 

 the crown. It is highly probable that its foot will slip into one of 

 these crevices, engage the pollen masses much as the pin did, 

 and pull them out as the foot is withdrawn. The insect flies to 

 another flower where it may come in contact with the stigmatic 

 surface and deposit some of the pollen ; often, however, its foot 

 is caught too tightly and it dies. 



The fruits are follicles, many of whose seeds are copiously 

 provided with silky hairs, collectively called a coma, which 

 aid in distribution. These comae are dyed and used extensively 

 for ornamentation. 



KEY TO GENERA 



Flowers green in umbels Acerates p. 24- 



Flowers not green in umbels Asclepias p. 24J 



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