2l8 



THE FLOWER 



direct part in the production of fruit, but are for show 

 merely. Their show, however, is far from being a vain and 

 empty one, as we shall see in Sections 330-338. 



311. Monoecious and Dioecious Plants. — When both 

 kinds of flowers, staminate arid pistillate, are borne on the 

 same plant, as in the oak, pine, hickory, and most of our 

 common forest trees, they are said to be monoecious, a 

 word which means "belonging to one household," and 

 dioecious, or " of two households," when borne on separate 

 plants, as in the willow, sassafras, and black gum. Draw 

 a flowering twig of oak, or other amentaceous (ament- 

 bearing) tree. Where are the fertile flowers situated 1 

 Notice how very much more numerous the staminate 



flowers are than the fertile ones. 



312. Advantages of the Uni- 

 sexual Arrangement. — The ab- 

 sence of parts in a flower is not 

 necessarily a mark of low organ- 

 ization, but may be the result of 

 adaptation to its surroundings. 

 It has been proved by experi- 

 ment that flowers will gener- 

 ally produce more vigorous and 

 healthy seed when impregnated 

 with pollen from a different 

 plant of the same species, and 

 unisexual flowers promote this 

 result by making it impossible 

 for any blossom to receive pol- 

 len from itself. 



438. — Twig of oak with both 

 kinds of flowers : / fertile flowers ; 

 s, s, staminate ; u, pistillate flower, 

 enlarged ; d, vertical section of 

 pistillate ilower, enlarged; c, por- 

 tion of one of the sterile aments, 

 enlarged, showing the clusters of 

 stamens. 



313. Suppression or Abortion of Organs. — Sometimes 

 this advantage is secured by the suppression of one or the 

 other set of organs in different flowers. In the pistillate 

 flowers of the persimmon the aborted stamens are quite 

 conspicuous, though entirely sterile, producing not a grain 

 of pollen. Rudimentary (undeveloped) organs of this kind 



