108 ELEMENTARY STUDIES IN INSECT LIFE 



Plants with Special Adaptations for Bringing About Cross- 

 fertilization. The milkweed family 1 illustrates one of the 

 many wonderful designs brought about by plants to in- 

 sure cross-fertilization. The milkweed blossom is to be 

 considered one of our highly specialized forms, and the 

 high degree of development is due in a great measure to 



FIG. 88. Entire flower of the milkweed (Asclepiodora viridis). Enlarged. 

 a a, location of corpusculum ; d, longitudinal slit which separates the anthers, and 

 into which insect draws its leg ; e, cucullus ; /, petal ; fir, sepal. 



the actions of insects. The flower structure' must be 

 understood before the work of the insect can be appre- 

 ciated. The blosstan used to illustrate the arrangement 

 of the parts is that of Asclepiodora v'uidls, or green 

 milkweed. The five minute sepals (Fig. 88) are sit- 

 uated beneath and alternating with the five well-devel- 

 oped petals. By bending these downward as in the fig- 

 ure, the inner mechanism can be more easily observed. 

 Five hollow, fleshy, leaf-like organs immediately 

 within, are attached to the central column. These arc 

 termed collectively cuculli, or singly cucullus. (Fig. 

 88.) This fleshy column is made by the union of the five 

 staminal filaments, each bearing at its upper end an 



lAsclepiadacecv. 



