SEED-BEARING PLANTS 477 



tion of flower-structure (Fig. 3 59) . The deeply five-parted 

 and reflexed corolla bears a crown of five "hooded" bodies, 

 in each of which there arises a pointed, incurved "horn" 

 (Fig. 360). The anthers are more or less united around the 

 stigma, and each cell contains a waxy, pear-shaped pollen- 

 mass (poltinium). The pollinia of adjacent anthers adhere 

 in pairs to cleft glands that grow one on each of the five 

 angles of the stigma. As bees climb over the flowers in 

 search of nectar in the bottom of the hoods, their legs 

 are drawn through tiny slits, and catch the cleft gland 



FIG. 361. Milkweed (Asclepias).^ Pollen-mass (pollinium), showing 



germination. 



when pulled out. Often the gland cannot be loosened, 

 and the legs of the insects are pulled off and left attached 

 to the flower. When the insect visits another flower the 

 pollen-masses (which by this time have twisted and 

 folded together) become inserted into the stigmatic 

 chamber of the second flower, where they germinate, 

 sending out numerous pollen- tubes (Fig. 361). On ac- 

 count of the complicated nature of this process, pollina- 

 tion often fails, so that only a small percentage of the very 

 numerous flowers produces seed. After fertilization, the 

 carpels increase enormously in size, and ripen into a pod, 

 filled with a large quantity of flat, thin seeds, each of 



