TEE DISPERSION OF SEEDS 339 



419. Some seeds may be carried long distances 

 by water. If wild rice is sown near the source 

 of a stream, it will gradually work down stream, 

 partly, perhaps, through the agency of birds, but 

 more directly by means of the water. The 

 "sea- beans" which are often so plenty on certain 

 coasts of Florida are leguminous seeds carried up 

 from the West Indies by ocean currents. The 

 cocoa-nut is the example most commonly cited of 

 dispersion by water. Its buoyancy and impervious 

 husk fit it to be carried very long distances on 

 the sea. 



420. A few plants have explosive fruits, by 

 means of which the seeds are dispersed for a 

 short distance. We have already seen some of 

 them (316, 316a, 3166, 331). 



421. The seeds of some plants germinate irregu- 

 larly, part of them coming up the first year and 

 others, from the same tree, not until the second 

 or third year. Many hard and bony seeds, like 

 those of the haws and hawthorns, are of this cate- 

 gory. By extending the germination over two or 

 three years, the plant may have more chances of 

 finding a condition in which it can thrive. 



422. The dispersion of plants depends, therefore, 

 upon two sets of factors: the structure of the 

 seed itself, which allows it to be disseminated by 

 wind or other means; and the physical conditions 



