POLLINATION 129 



Usually fertilization takes place only between plants of 

 the same species or kind. 



261. In many cases the pistil has the power of select- 

 ing pollen when pollen from two or more sources is applied 

 to the stigma. Usually the foreign pollen, if 



from the same kind of plant, grows and per- 

 forms the office of fertilization, and pollen from 

 the same flower perishes. If, however, no 

 foreign pollen arrives, the pollen from the 

 same flower may finally grow and fertilize 

 the germ. 



262. In order that the pollen may grow, the 203 

 stigma must be ripe. At this stage the stigma Pollen grain 



11 i. J 4.' J-- 1 A germinating. 



is usually moist and sometimes sticky. A ripe Greatly mag- 

 stigma is said to be receptive. The stigma 

 may remain receptive for several hours or even days, 

 depending on the kind of plant, the weather, and how soon 

 pollen is received. When fertilization takes place, the 

 stigma dies. Observe, also, how soon the petals wither 

 after the stigma has received pollen. 



263. POLLINATION. The transfer of the pollen from an- 

 ther to stigma is known as pollination. The pollen may 

 fall of its own weight on the adjacent stigma, or it may be 

 carried from flower to flower by wind, insects, or other 

 agents. There may be self-pollination or cross-pollination. 



264. Usually the pollen is discharged by the bursting 

 of the anthers. The commonest method of discharge is 

 through a slit on either side of the anther (Fig. 202). 

 Sometimes it discharges through a pore at the apex, as in 

 azalea (Fig. 204), rhododendron, huckleberry, winter- 

 green. In some plants a part of the anther wall raises or 

 falls as a lid, as in barberry (Fig. 205), blue cohosh, May 

 apple. The opening 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. 



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