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OR GANIC E VOL UTION 



insects which visit their blossoms. The petals of the 

 flowers usually secrete nectar, which is attractive to insects, 

 and many blossoms have an odor which also serves to 

 attract insects. The nectar is a sweet fluid secreted by 

 small glands, or nectaries, on the bases of the petals. It 

 is this nectar which bees gather and make into honey. 

 The odors of blossoms are caused by the presence of 

 volatile oils usually also secreted by the petals. These 



odors may be 

 such as are aoree- 



O 



able to our nos- 

 trils, as are the 

 odors of the rose, 

 the sweet violet, 

 the trailing arbu- 

 tus, or they may 

 be to us disa- 

 greeable, like the 

 odors of the car- 

 rion-flower and 

 skunk-cabbage ; 

 but, whether agreeable to us or not, they serve to secure the 

 visits of insects, and it is apparently because of this attrac- 

 tiveness to insects, and the advantage of cross-fertilization 

 in which the insects aid, that these odors and the nectar 

 have been developed. Many insects also seek the pollen 

 in the blossoms, using it as food, and most plants form more 

 pollen than is needed to fertilize their ovules, thus having 

 a surplus supply upon which insects may draw without much 

 or any injury to the plant. 



The insects which come to the blossoms to gather pollen 



FlG. 45. A bee, shouing the liairs on the head, body, and legs. 

 Pollen grains are shown caught in the hairs on the legs. 



