448 



STRUCTURE AND LIFE HISTORIES 



Such is the case in the willow, hop, ailanthus and, of course, 

 the cycads. When the staminate and pistillate flowers 

 occur on the same plant, either on the same branch or 

 axis, as in cat-tail, "Job's tears," begonia, et cetera (Figs. 



Fig. 332. — Inflorescences of the birch {Betula sp.). Below, the staminiiU' 

 flowers in large, pendant catkins; above, the pistillate catkins, erect. 



330-332, 375) or on separate branches, as in Indian 

 corn, arrow-leaf, and others (Fig. 333), the species is 

 monoecious. 



Since stamens and pistils are necessary to the formation 

 of seeds they are called the essential organs of the flower. 

 A flower like the tulip, rose, water-arum, or buttercup 

 (Fig. 345), having both kinds of essential organs, is a 

 perfect flower. 



