294 HOW CEOPS GKOW. 



ingly, constitute a perfect flower even in the absence of 

 calyx and corolla. 



The flower of buckwheat has no corolla, but a white or 

 pinkish calyx. 



The grasses have flowers in which calyx and corolla are 

 represented by scale-like leaves, which, as the plants ma- 

 ture, become chaff. 



Li various plants the stamens and pistils are borne in 

 separate flowers. Such are called monoecious plants, of 

 which the birch and oak, maize, melon, squash, cucumber, 

 and oftentimes the strawberry, are examples. 



In case of maize, the staminate flowers are the " tas- 

 sels " at the summit of the stalk ; the pistillate flowers 

 are the young ears, the pistils themselves being the " silk," 

 each fiber of which has an ovary at its base, that, if fer- 

 tilized, developes to a kernel. 



Dioecious plants are those which bear the staminate 

 (male, or sterile) flowers and the pistillate (female, or fer- 

 tile) flowers on different individuals ; the willow tree, the 

 hop-vine, and hemp, are of this kind. 



Fertilization and Fructification. The grand function 

 of the flower is fructification. For this purpose the pollen 

 must fall upon or be carried by wind, insects, or other agen- 

 cies, to the naked tip of the pistil. Thus situated, each 

 pollen-grain sends out a slender tube of microscopic diam- 

 eter, which penetrates the interior of the pistil until it en- 

 ters the seed-sack and comes in contact with the ovule or 

 rudimentary seed. This contact being established, the 

 ovule is fertilized and begins to grow. Thenceforward 

 the corolla and stamens usually wither, while the base of 

 the pistil and the included ovules rapidly increase in size 

 until the seeds are ripe, when the seed-vessel falls to the 

 ground or else opens and releases its contents. 



Fig. 62 exhibits the process of fertilization as observed 

 in a plant allied to buckwheat, viz., the Polygonum con- 



