156 Fertilization of Flowers. 



kinds occur on different plants, that is, the staminate on one plant 

 and the pistillate on another plant of the same species, the inflor- 

 escence is dioecious. With this explanation of the principal technical 

 terms immediately connected with our suhject, the process of fertili- 

 zation may be more fully described. 



When the pollen grains have been placed upon the receptive stigma, 

 they soon germinate under the influence of the moist ure supplied by 

 it. Each protrudes a slender tube or filament which grows downward 

 through the tissues of the pistil, carrying within itself the contents 

 of the pollen cell. Upon reaching the ovary, the advancing apex of 

 the tube enters the aperture of the ovule, into which the contents are 

 transferred. Then the ovule begins to develop its embryo and to 

 grow into a perfect seed. Without the influence it receives from the 

 pollen it develops no embryo and does not become a seed. In such a 

 case, the plant is sterile. Should fertilization wholly fail in any 

 species, the plant could not be propagated by seed. In most cases, if 

 fertilization does not take place not only seed fails to develop, but 

 also the ovaries or seed vessels; consequently no fruit is produced. In 

 a few instances, the ovaries grow for a time, but at length, as if be- 

 coming aware of the uselessness of their development, they wither and 

 drop from the plant prematurely. In some cases, as in the banana, 

 pineapple and other seedless fruits, they develop sufficiently to an- 

 swer the purposes of man, who makes use of them for food, but they 

 are valueless for the purposes of reproduction. 



How is the poll< n transfer If m the anthers to the stigmas? The 

 agents chiefly employed are water, gravity, birds, winds and insects. 

 Of these, winds and insects are by far the most important if we have 

 regard to the number of species whose pollen is transferred by them. 

 Plants which depend on the wind for the transmission of their pollen 

 are called anemophilous or wind-loving plants; those which depend on 

 insects are called entomophilous or insect-loving. 



Examples may be given illustrative of the action of these agents. 

 The eel-grass, Vullixneria spiralis, grows in ponds and sluggish 

 streams. Its flowers are dioecious. The pistillate flowers are raised, 

 by long slender flowering stems to the surface of the water where they 

 float, lying upon their sides and having their stigmas just at the sur- 

 face. The staminate flowers are produced on other plants and are 

 held by their short stems near the bottom of the water. Just before 

 the buds open they break from their support, rise to the surface, expand 

 and shed their pollen on the water. This is carried by the current or 

 Avafted by the winds till it comes in contact with the stigmas of the 



