THE FLOWER. 



59 



reach the nectar at the bottom, is at the upper side of the 

 orifice. The flower cannot self-fertilize. A good-sized 

 insect, flying from blossom to blossom and plant to plant, 

 must transport pollen from the one to the stigma of the 

 other."— (Gray.) 



76. The composite flowers, such as the Rudbeckia, 

 Heliopsis (Fig. 136), Sunflower, etc., are additional exam- 

 ples of proterandry. The anthers are syngenesious, and 

 discharge the pollen early, which is pushed out of the tube 

 by the elongating 

 pistil (Fig. 136, II, 

 p). The latter is not 

 as yet in a receptive 

 condition, and more- 

 over the pollen can- 

 not be applied to the 

 Btigraatic surfaces, 

 for they are on the 

 inner sides of the 

 forks or branches of 

 ' the tip of the style. 

 These do not spread 

 until the pistil has acquired its full length, and then curv- 

 ing outwards, the adjacent pollen is still prevented from 

 access to the stigma (Fig. 136, III, st). The conspicuous 

 ray-flowers (Fig. 136, Kg) doubtless serve for the attraction 

 of the many visiting insects, and they, by their more or 

 less hairy bodies, convey the adhering pollen (Pig. 136, IV) 

 from some flowers to the exposed stigmas of others; and 

 thus cross-fertilization is effected. Other proterandrous 



Fig. 136. Heliopsis tavis: I, Section of head of flowers ; //, Floret immature; 

 ///.Floret, with mature stigma ; /F, Pollen grain; r«, involucre ; ^^yZ, disk-floret ; 

 lig^ ray -flowers; ack, acheuia; cA, pale or chaff; p, pollen ; sf^ stigma. 



X22«. 



