PASSIVE MIGRATION. 357 



they attach themselves by buds, and bring forth new 

 colonies of individuals of their species. 



Influential as these active migrations of most animals 

 and many plants are, yet alone they would by no 

 means be sufficient to explain the chorology of organisms. 

 Passive Tnigrations have ever been by far the more import- 

 ant, and of far greater influence, in the case of most plants 

 and in that of many animals. Such passive changes of 

 locality are produced by extremely numerous causes. Air 

 and water in their eternal motion, wind and waves with 

 their manifold currents, play the chief part. The wind in 

 all places and at all times raises light organisms, small 

 animals and plants, but especially their young germs, animal 

 eggs and plant seeds, and carries them far over land and 

 seas. Where they fall into the water they are seized by 

 currents or waves and carried to other places. It is well 

 known, from numerous examples, how far in many cases 

 trunks of trees, hard shelled fruits, and other not readily 

 perishable portions of plants are carried away from their 

 original home by the course of rivers and by the currents 

 of the sea. Trunks of palm trees from the West Indies are 

 brought by the Gulf Stream to the British and Norwegian 

 coasts. All large rivers bring down driftwood from the 

 mountains, and frequently alpine plants are carried from their 

 home at the source of the river into the plains, and even 

 further, down to the sea. Frequently numerous inhabitants 

 live between the roots of the plants thus carried down, and 

 between the branches of the trees thus washed away there 

 are various inhabitants which have to take part in the 

 passive migration. The bark of the tree is covered with 

 mosses, lichens, and parasitic insects. Other insects, spiders, 



