78 



Asclepladaceae. 



la, effectively sheltering the nectar, which is secreted by the 

 ovary and occupies the lower part of the tube. The length 

 of the tube prevents short-tongued insects from getting the 

 nectar. Mueller thinks the honey bee can obtain only a 

 pait of the nectar. The stamens and pistil mature at the 

 same time. An insect in sucking the nectar first comes in 

 contact with the pollen, then with the stigma which is in- 

 serted lower down. Pollen does not adhere to a dry surface 

 but, must be moistened with nectar. Self-pollination takes 

 place in the absence of cross-pollination. 



The Milkweeds are as interesting in their 

 adaptations as are the orchids. 

 Gomm&a Milkweed. Hildebrand and Mueller long ago 

 called attention to the adaptations in this flower {Asclepias 

 cornuti.) The deeply five parted corolla is of purple color. 

 J Next to the corolla is a crown of 



five hooded bodies seated on the 

 stamens. The five stamens are 

 attached to the corolla, the fila- 

 ments are united in a tube which 

 encloses the pistil, and the anthers 

 adhere to the stigma. Unlike the 

 pollen of orchids, milkweed al- 

 ways has a pair of pollinia. They 

 are pear shaped and of yellow 

 waxy appearance. They hang by 

 a curved stalk from a dark colored 

 disc. These pollen masses are 

 taken out by insects as they suck 

 the nectar from the glands. The pollinia are attached to the 

 insect's hairs, legs and tongue. Charles Robertson, in an ex- 

 cellent account of plants belonging to this family, finds that 



PIG. 30. 

 Fig 30. Milkweed. Pollinia 

 of Aaclepiae cornuti; 2, flower 

 more magnified with some 

 parts removed. 



