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 {Belula Sp.). Below, the staminate 

 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. 34s), having both kinds of essential organs, is a 

 perfect flower. 



