150 PLANT BIOLOGY 



duce great quantities of pollen, for much of it is wasted. 



They usually have broad stigmas, which expose large 



surfaces to the wind. They are usually lacking in gaudy 



colors and in perfume. Grasses and pine trees are typical 



examples of ariemophilous plants. 



In many cases cross-pollination is insured because the 



stamens and pistils are in different flowers (diclinous). 



Monoecious and 

 dioecious plants 

 may be polli- 

 nated by wind or 

 insects, or other 

 agents (Fig. 204). 

 They are usually 

 wind - pollinated, 

 although willows 

 are often, if not 

 mostly, insect- 

 pollinated. The 

 Indian corn is a 

 monoecious plant. 

 ^ The staminate 



FIG. 204. FLOWERS OF BLACK WALNUT: two pis- flowers are in a 

 tillate flowers at A, and staminate catkins at B. 



terminal panicle 



(tassel). The pistillate flowers are in a dense spike (ear), 

 inclosed in a sheath or husk. Each " silk " is a style. 

 Each pistillate flower produces a kernel of corn. Some- 

 times a few pistillate flowers are borne in the tassel and a 

 few staminate flowers on the tip of the ear. Is self-fertili- 

 zation possible with the corn? Why does a "volunteer" 

 stalk standing alone in a garden have only a few grains 

 on the ear ? What is the direction of the prevailing wind 

 in summer ? If only two or three rows of corn are 



