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 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 
moncecious. 
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. 
