FLOWERS AND INSECTS 



247 



the several stamens and the single carpel are in a cluster 



enclosed in a boat-shaped structure (keel) formed by two 



of the petals (Fig. 241). The stigma is at the summit of 



the style and projects somewhat beyond the pollen sacs, 



some of whose pollen lodges on a hairy zone on the 



style below the stigma. While the stigma is not alto- 



gether secure from receiving some pollen, the position 



does not favor it. The 



projecting keel is the nat- 



ural landing place for a 



bee visiting the flower; 



and it is so inserted that 



the weight of the insect 



depresses it, and the stig- 



ma comes in contact with 



its body. Not only does 



the stigma strike the 



body, but by the glan- 



cing blow the surface of 



the style is rubbed against 



the insect; and upon this 



style, below the stigma, 



the pollen has been shed 



and is rubbed off against 



, . . , 



the insect. At the next 



flower Visited the Stigma 

 IS likely to Strike the pol- 



len obtained from the pre- 



FIG. 242. Longitudinal section of flower of 

 iris, showing a single stamen between the 

 drooping petal and the petal-like style; 

 the stigmatic shelf is seen above the 

 stamen, at the top of the style; the nectar 



vious flower, and the style 



will deposit a new supply of pollen. It is interesting to 

 press down slightly the keel of such a flower and see the 

 style apparently dart out. 



In the iris or common flag, each stamen is in a kind of 

 pocket between the petal and the petal-like style; while 

 the stigmatic surface is on the top of a flap or shelf which 

 17 



