144 



ORGANS OF VEGETATION 



Fertilization may be classified under three general heads: 

 (1) close fertilization, which occurs when the pistil is fertilized 

 by pollen from stamens growing in the same flower with the pistil 



or from other flowers on 

 the same plant; (2) cross 

 fertilization, which occurs 

 when ovules are fertilized 

 by pollen from other plants 

 of the same species; (3) hy- 

 bridization, which occurs 

 when the ovules are fer- 

 tilized by the pollen of 

 some other nearly related 

 species. 



Pollination may be ac- 

 complished through the 

 action of the wind, which 

 blows the pollen from the 

 stamens of one flower 

 upon the pistils of another 

 flower as in the case of the 

 pines and oaks; through 

 the visits of insects, which 

 carry pollen from one 

 flower to another as in the 

 case of willows and other 

 dioecious plants; and lastly 

 through hand pollination 

 or other human agency. 

 The last method enables 

 us to know both parents 

 of the seed we are growing 

 and naturally gives the 



Fertilization of the ovule. most satisfactory results. 



The pollen tubes pass through the stigma and style, m inmvA nnrrAnt rpnlt<a if 

 finally entering the cavity (locules) of the ovary. 



is usually found best to 



remove all the anthers of the flowers upon which we wish to 

 experiment sometime before their maturity, and after the flower 



