Plants in Relation to Man 489 



pollinating. On certain plants, as the wild violet, wood sorrel, 

 and pansy, one may sometimes find small flowers which have 

 no petals and never open ; but as they produce seed they must 

 be self-pollinated. In the culinary pea pollination occurs be- 

 fore the blossoms open. The anthers burst and provide the 

 stigmas with pollen grains while the first petal to appear is 

 still green. But most plants depend upon cross-pollination, 

 and have adaptive structures to prevent close-pollination and 

 to make use of such agencies as water, wind, or insects to secure 

 cross-pollination . 



235. Wind-pollinated plants. The corn plant, several 

 kinds of grasses, many trees, including spruce, pine, and cone- 

 bearing trees generally, maple, elm, willow, birch, elder, and 

 certain shrubs, depend for pollination upon the most universal 

 agency, the wind. Many of these plants produce staminate 

 and pistillate blossoms on the same individual, as in the corn ; 

 while others produce these blossoms on different individual 

 plants. The staminate blossoms in both classes are many 

 times more numerous than the pistillate. All plants dependent 

 upon the wind for cross-pollination produce a superabundance 

 of pollen, for naturally an immense amount must be wasted by 

 the wind. Corn, willow, and hazel are familiar examples of this 

 prodigality. 



Adaptive features. The corn shows a remarkable adapta- 

 tion to wind-pollination. The tassel is at the top of the stalk, 

 where it is most exposed to the wind, and the pistillate flower 

 is lower and quite inconspicuous. The light, feathery pollen 

 is easily detached and scattered by the slightest breeze over 

 neighboring plants, the silken stigmas of which are so brushy 

 and sticky that pollen once touching is held. 



All wind-pollinated plants have peculiar adaptive features. 

 Some produce pollen that is powdery or feathery, or equipped 

 with wings, or with bladders, as the pine. The stigma on many 

 is an interesting mechanism. Certain grasses, such as timothy, 

 raise feathery heads high above the rest of the plant. On some 



