88 PLANT BIOLOGY 



light, dry pollen. On another part of the plant the ears ot 

 corn develop. Each ear consists in part of clusters of pistillate 

 flowers, and the threads of silk represent the styles of the 

 pistils. Farmers know that a single corn plant, growing in a 

 place apart from other corn plants, will not form vigorous 

 ears. To secure a good crop, pollen must be carried from the 

 tassels of one plant to the silk of another, and this is accom- 

 plished in a garden or a corn field by the wind. Much more 

 pollen must be produced, however, by wind- than by insect- 

 pollinated flowers, since in the former case a great deal more 

 is wasted. Many wind-pollinated flowers, such as grasses, 

 have feathery styles to catch and hold the pollen brought by 

 the wind. 



98. Summary and definitions. 



Floral envelopes of a flower = calyx + corolla. 



Calyx: composed of sepals (often green in color); 



principal use, to inclose and help protect the 



essential organs from cold, rain, or biting 



insects. 

 Corolla: composed of petals (usually bright colored); 



principal use to attract insects and so secure 



cross-pollination. 



Essential organs of a flower = stamens + pistils. 



Stamens: usually composed of filament and anther; 

 use, to produce pollen grains, each containing 

 a sperm-cell. 



Pistil: usually composed of ovary, style, and stigma 

 (or stigmas) ; use, to produce ovules, each con- 

 taining an egg-cell, and to insure pollination, 

 germination of pollen grains, and fertilization. 



