Wind 61 



paratively near to plant-covered areas, at least in flat regions, it is 

 intelligible that the possibility of wind-transport over great distances 

 should be doubted, as, for example, the transport of seeds and spores 

 to distant islands, or, at most, admitted only in the case of spores. 



The fact that a large proportion of the vegetation of volcanic is- 

 lands, situated a considerable distance from continents, consists chiefly 

 of ferns, and the occurrence on coral islands of ferns and certain 

 species of flowering plants which could not well be introduced except 

 by wind, afford evidence of the far-reaching influence of air-currents. 

 There are, indeed, several observers who acknowledge the importance 

 of wind-action as a factor in the colonisation of such districts. 

 Engler 1 , in his work on island floras and the floras of tropical moun- 

 tains, has laid stress on the view that light seeds are carried over wide 

 areas in the higher currents of the atmosphere during periodically 

 recurring strong winds. In his comparative treatment of the floras 

 of the larger islands in the Pacific Ocean, especially of the Sandwich 

 islands, he arrives at the conclusion, based on his study of the means 

 of dispersal of fruits and seeds, that of the 675 species in the Sand- 

 wich islands 140 spore-bearing plants and 14 seed-plants owe their 

 distribution to wind ; in the case of 322 species dispersal by birds is 

 possible (56 species by coast-birds ; 241 in the intestines of birds, and 26 

 on their feathers). The fact that of the 669 indigenous species in the 

 Sandwich islands not less than 500 (74'6 %) are endemic, demonstrates 

 the exceptional dispersal of seeds by wind and by birds over such 

 long distances as are in question as regards these islands. Before 

 Treub called attention to the important role of wind in the dissemina- 

 tion of plants, Beccari 2 had arrived at the conclusion, as the result 

 of his observations in the Malay Archipelago, that a considerable 

 number of species are confined to mountain-summits separated from 

 one another by as much as 3200 kilometres [2000 miles], and further 

 that nearly related species are separated from one another by long 

 distances. 



According to Beccari the mountain-tops of the Malay Archipelago 

 occupy a position where, during part of the year, particularly from 

 November to April at the time of the west monsoon, the strength and 

 constant direction of the wind are maintained for a longer time than 

 in the lower regions and on the sea-coasts. It is therefore clearly 



1 Engler, A. Versuch einer Entwicklungsgeschichte der Pflanzenwelt, ir. Teil. 

 Die extratropischen Gebiete der Siidlichen Hemisphare und die tropischen Gebiete, 

 Leipzig, 1882. 



2 Beccari, O. Malesia, Vol. i. Fasc. iii., 1878, pp. 214-235. 



Beccari, O. " Beitrage zur Pflanzengeographie des Malayischen Archipels " (ab- 

 stract by A. Engler). Bot. Jahrbiicher, i. Bd., 1881. 



