Fruits and Seeds 



261 



carried by the air depends on the amount of surface it exposes in 

 proportion to its weight. The greater the surface in proportion 



Fig. 168. Fruits frequently transported by wind: A, maple; B, elm; C, ash. 



F 



D. bass- 



wood ; E, dandelion ; and F, clematis. 



to the weight, the more the resistance it offers to falHng through 

 the air and the farther it may be carried by the wind. The 

 plumes of the milkweed, thistle, dandehon, willow, and cotton- 

 wood increase the surface tens, hundreds, or thousands of times 

 without materially increasing the weight. Consequently, these 

 seeds may be carried many miles if they get well up into the air 

 at the start. Maple, elm, ash, and catalpa have relatively large 

 surfaces (wings) for their mass and they are easily blown about. 

 The chief disadvantage of wind as a disseminator of seeds is that 

 so many seeds are carried to habitats where germination will not 

 take place. 



Many seeds are transported by streams and lake currents. 

 During spring freshets enormous numbers of seeds are picked up 

 from the overflowed lands and transported downstream. After 

 floods in the Mississippi and other large rivers one may find nu- 

 merous rows of seedlings extending along the sides of the valley at 

 definite levels, marking the height of a rather prolonged stage of 

 high water, during which the seeds were washed ashore. Similar 

 lines of seedings are not uncommon along the shores of the 

 Great Lakes at certain times of the year. Here they are soon 

 destroyed by storm waves. The seeds most commonly trans- 

 ported by water are those of water, shore, and bottom-land plants. 



