80 



AGRONOMY 



Pollination. Stamens and carpels are the only organs in 

 the flower that are necessary to the production of seeds, and 

 for this reason are often distinguished as the essential organs. 

 A considerable number of plants, of which the willow and 

 cottonwood are examples, have only these two kinds of 



organs, showing very 

 clearly that the others 

 are not necessary. In 

 some species the sta- 

 mens and pistils are 

 in separate flowers, as 

 in the pumpkin and 

 cucumber; in others 

 they may be on sep- 

 arate plants, as in the 

 willow. Even when 

 both sets are found in 

 the same flower, as in 

 the lily and most of 

 our common plants, 

 they are usually sepa- 

 rated from each other 

 by a distance too great 

 to be bridged with- 

 out the aid of the 

 FIG. 70. Trillium wind, birds, insects, 



A plant in which the monocotyledon number an( ] other agencies. Of 

 (three) is especially prominent 



these, the two most 



important are undoubtedly wind and insects. Wind-pollinated 

 flowers are generally inconspicuous, lacking sepals and petals 

 and producing neither perfume, pollen, nor nectar, since the 

 wind will work without pay ; but flowers that depend upon 

 insects and birds for pollination must provide a reward in 

 the form of nectar or extra pollen, and must advertise it by 



