POLLINATION 



129 



Usually fertilization takes place only between plants of 

 the saint' species or kind. 



2G1. In many eases 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. 



2G2. In order that the pollen may grow, the 

 stigma must be rive. At this stage the stigma Poll, ' n grain 



, . germinating. 



is usually moist and sometimes sticky. A ripe Greattymag- 



. , , . rm , . nitied. 



stigma is said to be receptive. 1 he 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. 



2(i.'i. 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 he self-pollination or cross-pollination. 



264. Usually the pollen is discharged by the bursting 

 of the anthers. The commonesl method of discharge is 

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

 Sometimes it discharges through ;i pon at the apex, as in 

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

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



falls as ;i lid, as in barberrj (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 /" '/< liisr, . 



I 



