306 



TYPICAL FLOWERING PLANTS 



tion. Since this has been known, nursery men and gar- 

 deners have taken advantage of cross-pollination to 



improve their stock 

 and to produce new 

 varieties of fruits and 

 vegetables. Much of 

 Luther Burbank's 

 w r ork has been based 

 on cross-pollination. 



Plants have a num- 

 ber of devices for pre- 

 venting self-pollina- 

 tion. The anthers, 

 for instance, may be 

 turned away from the 

 stigma ; or the pistil 

 may be so tall that 

 no pollen can get on 

 it from the stamens of the same flower; or the stigma 

 may be ripe and the ovules started to develop before 

 the stamens of the flower are ready to shed their pollen 

 (Figure 317). 



While it is the rule that plants avoid self-pollination and 

 self-fertilization, a few have no other way of producing 



Figure 31 7. — Salvia. 



A flower in which the stamens mature at 

 one time and the pistils at another. 



Figure 318. — Easter Lily. 



seeds. This is true of cleistoofamous flowers. The one 

 or two stamens which they develop contain sufficient 



