308 



ELEMENTARY BIOLOGY 



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. 



361. Water pollenation. Another agent 

 that is effective in distributing pollen for 

 plants is water. This, of course, is con- 

 fined to plants that live in the water. 



FIG. 140. Pollenation 

 by insects 



In the lady's slipper and 

 in many other flowers, in- 

 sects alighting on the co- 

 rolla crawl into the interior, 

 guided by the form and the 

 markings. In many flowers 

 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 

 among the orchids, depend 

 upon single species of in- 

 sects for their pollenation 



A good example of pollen transfer by water 

 is furnished by the tape-grass (VaUisneria), 

 which lives near the edges of ponds (see 

 Fig. 138). 



362. Bird pollenation. Next to the 

 wind, the most common moving agents 

 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 



