FERTILIZATION AND POLLINATION 



135 



224. Flower of larkspur. 



225. Envelopes of a larkspur. There 

 are five wide sepals, the upper 

 one being spurred. There are 

 four small petals. 



ent plants. Fertilization resulting from self- or close-pollina- 

 tion is close-fertilization. Fertilization resulting from cross- 

 pollination is cross-fertilization. In 

 many cases cross-pollination is 

 essential for good seed or fruit 

 development. Corn, if close-pol- 

 linated, pro- 

 duces imperfect 

 ears. Culti- 

 vated plants 

 frequently ex- 

 hibit decreased 

 vigor by close- 

 pollination. 



279. Usually 

 the pollen is dis- 

 charged by the 

 bursting of the anthers. The commonest method of discharge 

 is through a slit on either side of the anther. (Fig. 218.) Some- 

 times it discharges through a pore at the apex, as in azalea 

 (Fig. 220), rhododendron, huckleberry, wintergreen. In 

 some plants a part of the anther wall 

 raises or falls as a lid, as in barberry (Fig. 

 221), blue cohosh, May apple. The open- 

 ing of an anther (as also of a seed-pod) is 

 known as dehiscence. When an anther or 

 seed-pod opens it is said to dehisce. 



280. Most flowers are so constructed as 

 to increase the chances of cross-pollination. 

 The commonest means of insuring cross- 

 pollination is the different times of matur- 

 ing of stamens and pistils in the same 

 flower. In most cases the stamens mature 

 first: the flower is then proterandrous. 

 When the pistils mature first the flower is 



226. Stamens of lark- 

 spur, surrounding 



the pistils. 



