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TEXTBOOK OF BOTANY 



eaten by insects ; these hairs perhaps bear also small drops 

 of nectar. If the insect is of the right size and strong enough, 

 it can push its way out through the opening at either side 

 of the flap ; certain bees, for example, can do this ; smaller 

 insects, such as flies, cannot, but remain inside the sac and 

 die there. On the under side of the flap (the side toward 

 the inside of the sac) is the stigma ; and on either side of 



the stigma is an anther, whose 

 pollen is held together in a 

 sticky mass. As a bee pushes 

 out beside the flap, its shoul- 

 der brushes against an anther 

 and carries away the mass of 

 pollen. Then, when the bee 

 enters another flower, its 

 shoulder brushes against the 

 stigma of that flower and 

 there deposits the pollen. 



As a rule, a flower of any 

 particular species may be 



FIG. 159. A lengthwise section 

 through the flower of a wild lady's- 

 slipper (Cypripedium acaule) ; a, one 

 of the three sepals ; b, a petal ; c, the 



anther of a fertile stamen; <Z, a sterile Pollinated by any one of a 

 stamen ; e, the stigma ; /, hairs at number of different kinds of 

 the bottom of the sac, g, which is 

 composed of a single petal; h, the 



ovary. 



insects ; but sometimes, as in 

 the case of the lady's-slipper, 

 the flower is so formed that 

 it can be pollinated only by an insect of about a certain 

 size ; and often, as in the columbine and in flowers like the 

 petunia, whose petals are united into a tube, the nectar can 

 be reached only by an insect with a proboscis of at least a 

 certain length. There are flowers that are adapted to 

 pollination by only one particular kind of insect (see 283 

 and 284 below). 



282. Pollen as Food for Insects. There are flowers 

 including the common anemone, the roses, and the hepaticas 

 ' which depend upon insects for pollination, but which form 



