308 



ELEMENTARY BIOLOGY 



FIG. 140. Pollenation 

 by insects 



360. Wind pollenation. The most common moving agency 

 that is able to act between plant and plant is the wind. The 

 abundance and the dryness of the pollen produced by many of 

 the common trees, and the frequency with 

 which pollen may be found in the dust at 

 certain seasons of the year, would lead us 

 to suspect that the wind is an effec- 

 tive agent in this matter (see Fig. 137). 

 A study of conditions on farms that pro- 

 duce corn, wheat, oats, and other grains 

 shows that these plants, as well as many 

 others, depend entirely upon the wind for 

 their pollenation. Indeed, it is sometimes 

 necessary to take special precautions to 

 prevent the wind from bringing to a 

 group of plants an undesirable kind of 

 pollen from a remote field, 

 in the lady's slipper and 361. Water pollenation. Another agent 



in many other flowers, in- , . r . . ..... . 



sects alighting on the co- that is effective in distributing pollen for 



rolla crawl into the interior, plants is Water. This, of COUrSC, is COn- 

 guided by the form and the 



markings, in many flowers fined to plants that live in the water. 



the arrangement of the 

 parts is such that the in- 

 sect must brush against the 

 stigma in going in, and 

 against the anthers in pass- 

 ing out. As a result the 

 animal carries pollen from 

 flower to flower. Many 



species of plants, especially 362. Bird pollenation. Next to the 

 among the orchids, depend wmc | tne most common moving agents 



upon single species of in- 



sects for their pollenation that go from flower to flower are flying 

 animals and birds and insects. Now we 

 know that not all birds or all insects can serve plants as 

 pollen carriers ; only those that regularly visit flowers can 

 be considered of importance in this connection. Certain 

 humming birds that visit flowers lap up the sugary fluid, or 



A good example of pollen transfer by water 

 is furnished by the tape-grass (Vallisneria), 

 which lives near the edges of ponds (see 

 Fig. 



