THE WORK OF FLOWERS 301 



wind. A good example of such a plant is the Corn: 

 the anthers (i.e., the "tassel") produce abundant 

 pollen, which is carried by the wind to the "silk"; the 

 strands of "silk" are long stigmas, with projections to 

 catch the pollen; the pollen-tube must grow down the 

 whole length of the " silk." Wind -pollinated plants 

 produce great quantities of pollen, since wind -pollina- 

 tion is a very wasteful process. The pollen from Pine 

 forests often forms a yellow coating on lakes or on the 

 ocean two hundred miles away, and has been mistaken 

 by peasants for showers of sulphur. The pollen- grains 

 of the Pine are provided with hollow vesicles, which 

 buoy them up in the air very much on the principle 

 of a box kite: these may be easily seen under the 

 microscope. 



In order to determine to what extent flowers are 

 dependent on insects (or wind) for pollination, it is 

 only necessary to enclose them, before the bud is open, 

 in paper bags (see page 289). If this be done, no 

 fertilization or setting of seed can take place unless 

 some of the pollen of the same flower arrives on the 

 stigma. This is said to be self-pollination, as opposed 

 to cross-pollination, which means bringing the pollen 

 from a different flower. 



Darwin made a series of experiments to determine 

 whether cross- or self-pollination is more advan- 

 tageous. He found that, in the case of the Morning- 

 glory, cross -pollination gave plants which in height 



