150 THE NATURE AND WORK OF PLANTS 



the pollen would fall away from instead of upon 

 the pistil of the same flower. Having guarded 

 against self-pollination, the plant must next be pro- 

 vided with means of securing pollen from other 

 flowers for all the pistils. The principal agencies 

 which it makes use of in this work are the wind 

 and animals, principally insects. 



205. T7ie ivind as an aid to pollination. — More 

 than ten thousand species are known to make use 

 of the wind as an agency in carrying the pollen from 

 one flower to another. In order to do this success- 

 fully great quantities of pollen are produced and 

 thrown into the air upon the opening of the pollen 

 sacs, and then float upon the currents of air, some of 

 them alighting upon the stigmas of other flowers. 

 The pines, oaks, beeches, hazels, birches, poplars, 

 walnuts, mulberries, and some maples throw their 

 pollen into the air and allow it to float to other 

 flowers in this manner. It is a matter of common 

 knowledge that when a single row of corn is planted 

 in a field with no other collection of the same in the 

 vicinity, generally no seeds are produced. This will 

 always be the case if the row is at right angles to the 

 prevailing winds. The pollen of the pines is often 



