302 BOARD OP AGRICULTURE. 



cryptogams are so small and light as to be readily borne to 

 distant regions by the winds, and the number produced by each 

 plant is usua ly very great, so that wherever favoring influences 

 exist the appropriate species are never long in making their ap- 

 pearance. The spores of alga; and other aquatic cryptogams 

 are distributed by running streams, waves and oceanic currents. 



The principal agent in the general distribution of the seed of 

 phenogamous plants is the wind. To favor this operation pro- 

 vision has been made in a variety of ways. Thus the heaths, 

 the grasses and the orchids generally have small and very 

 numerous seeds, and, in common with many other families, have 

 a dry fruit, which opens gradually and is shaken by the winds 

 until the contents are widely scattered in various directions. 

 Again, the needle-leaved trees generally produce winged seeds, 

 which, as the scales of the ripening cones separate, are wafted 

 away to considerable distances on the moving air. The small, 

 dry, one-seeded fruits of the compositaD, like the dandelion and 

 thistle, are often supplied with beautiful tufts of down or silky 

 bristles, which bear them aloft and float them through the 

 atmosphere like balloons. 



The seeds of the cotton, the silk weeds, willow herbs and 

 many others arc furnished with similar means of conveyance, 

 by which they are carried away from the ripening capsule. 



The violent hurricanes of warm regions must prove very 

 efficient in distributing seeds, even where they are not very 

 well provided with special apparatus for aerial navigation. 



Streams of fresh water and oceanic currents and the combined 

 influence of wind and wave are most important aids in plant 

 distribution. Not only are aquatic seeds and fruits thus widely 

 disseminated, but the fruits of the cocoa-nut, the seychelle and 

 other species of palm, the screw-pine and other large plants, are 

 wafted from island to island in the waters of tropical oceans, 

 while the floating masses of ice in the arctic regions often dis- 

 tribute the seeds of dwarf alpine species. Those currents of 

 air or water, which move east or west, will of course be more 

 useful in this work than those tending north or south, because 

 the latter would more frequently transport seeds to uncongenial 

 climes. 



A few species of plants have been supplied with an apparatus 

 for projecting the seeds and spores to some distance from the 



