THE WAY IN WHICH NEW PLANTS ARISE 149 



203. Spores of seed plants. — The sporophytes of 

 seed plants produce two kinds of spores. One is 

 formed in the stamen and forms the pollen grains, 

 and the other grows in the ovary and produces the 

 gametophyte which bears the egg cells. 



204. Pollination. — In order to complete the 

 life history of the plant it is necessary that the 

 pollen grains should be transported to the stigmas, 

 or upper extremities of the pistils, where they may 

 germinate and send a long tube down to the 

 ovaries. Furthermore, it is important in a great 

 number of species that the pollen from one plant 

 should be carried to the pistils of another, a pro- 

 cess termed by the botanist cross pollination. The 

 seeds and seedlings obtained by this method are 

 much stronger and represent the species more per- 

 fectly in most instances than those which result from 

 the action of the pollen upon the pistil of the same 

 flower. The various devices by which this cross 

 pollination is secured are almost without number. 

 One method by which the pollen of any flower 

 is kept from its own pistil is to have the stamens 

 and pistil mature at different times. In other 

 cases the stamens are below the pistils, so that 



