190 FLOWERS 



Dichogamy, which is the maturing of stamens and pistils 

 at different times, has resulted in the formation of protero- 

 gynous and proterandrous flowers. In proterogynous floicers 

 the pistil matures and is receptive of pollen before the stamens 

 mature. In proterandrcus flowers the stamens mature and 

 the pollen is distributed before the pistil matures. In both 

 of these kinds of flowers fertilization can occur only by cross- 

 pollination. 



FIG. 120. Hollyhock (Athcea rosed) mature stamens and undeveloped 

 pistils to the left, mature pistils but withered stamens to the right. 



Dimorphism. When a plant produces two types of flowers, 

 one having stamens with short filaments and pistils with long 

 styles, and one having stamens with long filaments and 

 pistils with short styles, such flowers are dimorphous] when 

 there are three forms of flowers with stamens and pistils of 

 three lengths, the flowers are trimorphous. 



Position of Reproductive Organs. In some flowers cross- 

 pollination is secured by the position of the reproductive 

 organs. 



In moccasin flower the insect must push aside the pistil 



