



114 DIFFUSION OF PLANTS. 



conveyance of seeds to them, either by water or birds. Some seeds 

 are furnished with wings and down as if intentionally for their con- 

 veyance, as the dandelion, thistle^ etc. The ash, fir, sycamore, etc., 

 have membranous wings and others have hooks. The migration of 

 plants is supposed to be facilitated by the currents of the sea. Thus 

 seeds from the W. I. Islands are transported in this way to the coast 

 of G. Britain, Norway, and Ireland. Most frequently, however, seeds 

 are destroyed by the effects of the water, or, from their greater specific 

 gravity, they sink in it. 



Currents of rivers also convey seeds to a great distance ; so that on. 

 the banks of streams are generally found a more varied vegetation than 

 in regions distant from them. Mountainous plants are brought down, 

 upon plains by these streams of water ; and seeds which do not vege- 

 tate on such elevated situations, but are readily caught or intercepted 

 when conveyed by the wind, are thus conducted to valleys where they 

 flourish. The wind, as we have elsewhere said, is also a constant 

 and active means in the dispersion of seeds, particularly the light 

 winged and pappous. Those which have hooked bristles are often con- 

 veyed on the coats of animals, whilst wandering from place to place. 

 Seeds conveyed and voided in a perfect state by birds are said to be 

 better fitted for germination than they were before ; and in this way 

 they are deposited in situations most favorable for their growth. 



Seeds conveyed by man are mostly productive. A ship from Good 

 Hope with bulbs on board was wrecked on the island of Guernsey, 

 when one getting astray, was propagated by the soil which now yields 

 the Guernsey lily, so as to afford an important branch of trade in its 

 roots. The potato is said by the Irish to have been introduced into 

 Ireland by the wreck of a vessel on its coast. A species of artichoke, 

 introduced by seeds from Europe at Buenos Ayres, now densely covers 

 a space of 900 miles, springing up to the height of 10 feet; and what 

 is remarkable, it annually and suddenly alternates with clover, neither 

 being able to drive the other out. Thus with many other plants when 

 once introduced, they either exterminate the natives of the soil, which 

 is most frequently the case, or they alternately prevail, as in the above 

 case. When one species of plants dies at a particular season, another 

 springs up and in its turn occupies the soil for a brief period. 



The extraordinary fruitfulness of some plants in seeds, is also to be 

 considered in the diffusion and propagation of their species. 32,000 

 seeds have been counted in a single poppy. The elm produces an- 

 nually 100,000 seeds. Each of these seeds is capable ofbecom- 

 ing an individual plant or tree, and if each were to grow up the 

 world might soon be covered with vegetation almost in despite the 

 efforts of man. Thus nature provides against all the contingencies to 

 which seeds are exposed as she does in the perpetuation of animals by 

 the multiplication of their eggs. The queen bee, for example, lays 



