THE FLOWER. 83 



As already intimated, the parts of the flower exhibit 

 the same general structure as that of the leaf, structure and 

 but with modifications corresponding to the Actions of 



the several 

 special functions that each part fulfills. parts, 



The calyx and corolla are protective, serving to guard 

 the parts within from frost and rain and the intrusion of 

 unwelcome visitors. They are also attractive, pi ora i enve i. 

 particularly the corolla, which is usually col- P es> 

 ored so as to attract bees and other color-loving insects. 

 They form, too, a part of the mechanism, often very pecu- 

 liar and interesting, by which pollination is effected. 



The stamens are usually far more modified than the 

 floral envelopes. The thickened anther, corresponding to 

 the blade of the leaf, produces pollen, the active 

 agent of fertilization. The pollen consists of 

 rounded cells, the walls of which are variously thickened, 

 frequently beset with spines, and, in some instances, 

 winged, thus facilitating their conveyance by insects or by 

 the wind. The cell contents are protoplasm, with one or 

 more nuclei, and a considerable quantity of food material, 

 such as starch, oil, and sugar. 



The pistil is simple or compound according as it is made 

 up of one or more than one carpellary leaf. 1 The ovules, 

 which afterwards become the seeds, originate as 

 cellular outgrowths from the margins of the 

 carpel. An ovule, when fully formed, consists of a cen- 

 tral mass of cells, called the nucellus, around which one, 

 or commonly two, protective coats are formed, and within 

 which a cell, called the embryo-sac, arises. It is in the 

 embryo-sac that the young embryo is developed. An 

 opening between the coats, called the micropyle, leads 

 down to the nucellus. The parts as described at once 



1 Cf . Gray, Structural Botany, p. 260 et seq. 



