888 



GEOGRAPHICAL DISTRIBUTION AND 



[Ch. XL. 



in all directions in whicli it is possible for it to spread from 

 tlie original point or centre wliere it was first formed. 



The most active of tlie inanimate agents provided by na- 

 ture for scattering the seeds of plants over tbe globe, are 



movements 



om 



To 



nnmber 



with downy and feathery appendages, enabling them, when 

 ripe, to float in the air, and to be wafted easily to great dis- 



gentle breeze. Other plants are fitted 



most 



means 



of the fir-tree, so that they are canght np by the wind 



as 



they fall 



om 



the cone, and are carried to a distance. 



Amongst the comparatively small nnmber of plants known 

 to Linnsens, no less than 138 genera are ennmerated as 



having winged seeds. 



As winds often prevail for days, weeks, or even months to- 



same direction, these means 



may sometimes 

 may be borne 



tempests 



mov 



forty miles an hour, and if the storm be very violent, at the 

 rate of fifty-six miles.-^ The hurricanes of tropical regions, 

 which root np trees and throw down buildings, sweep along 



miles 



may 



width 



means 



the vegetation of adjoining continents. 



Whirlwinds 



strumental 



& 



along heavy vegetable substances 



may 



to considerable distances. Slight ones 

 served in our fields, in summer, carrying up haycocks into 

 the air, and then letting fall small tufts of hay far and wide 

 over the country ; but they are sometimes so powerful as to 

 dry up lakes and ponds, and to break off the boughs of trees, 

 and carry them up in a whirling column of air. 



* Annuaire du Bureau des Longitudes. 



