FRUITS AND SEEDS 115 



canal without being injured. Birds carry the seeds of many 

 fruits and weeds on which they feed, and water fowl carry the 

 seeds of water plants. Squirrels and other rodents store seeds 

 of many kinds, especially nuts, which are frequently not recov- 

 ered but which grow under favorable conditions (Fig. 82). 



(c) Seed Dispersal by Water. Some seeds are carried on 

 the surface of streams and lakes, while others are carried by the 

 rapidly running water immediately following rains. Seeds 

 may be carried for short distances over the surface of the ground 

 during periods of heavy rainfall and for great distances on 

 streams, lakes and seas. They frequently lodge along the shores 

 or on distent islands and grow. The vegetation of coral and 

 volcanic islands frequently originates in this manner. 



(d) Seed Dispersal by Expulsion. Many plants have pecul- 

 iar mechanical devices by which seeds are thrown to considerable 

 distances. When the witch-hazel pods split open there is a pres- 

 sure which throws the seeds to a considerable distance. The 

 touch-me-not pods split and curl with sufficient force to throw 

 the seeds a considerable distance. The pods of the common vetch 

 or wild pea split and the two parts twist in such a manner as 

 to throw the seeds out. The so-called " squirting cucumber " 

 absorbs water and shoots the seeds to a considerable distance. 



(e) Seed Dispersal by Man. Of course, man carries the 

 seeds of his crop plants with him from place to place and in so 

 doing he also carries seeds of many weeds. He also carries the 

 seeds of many plants in bedding for live stock, in packing ma- 

 terial, and in the soil about the roots of living plants. Some are 

 carried from country to country in ballast in ships. Seeds fre>- 

 quently fall from railroad trains, grow and become established 

 in new localities. 



