INTRODUCTION. 



traveller as he penetrates an extensive forest. Every 

 morning he commences his journey, patiently pur- 

 suing the winding pathways through interminable 

 multitudes of trees and shrubs, till, when evening 

 arrives, he is hardly less fatigued with the mono- 

 tony of the scene than with the exertions of the 

 day. His feelings are the same as those at sea — 

 he is surprised at the interminable character of the 

 scene, and his ideas of space are measured by a 

 greater standard. He wonders at the vast multi- 

 tudes of vegetable beings ; whence they could 

 possibly have drawn nourishment to rear such solid 

 structures ; he speculates on their age, and lastly on 

 their use. In both cases the ideas of space are the 

 same, but they have received an impulse from the 

 novelty of the scene ; perhaps assisted also by the 

 perfect stillness, which reigns so completely in deep 

 forests, and during the heat of the day the silence is 

 more painful than on the wide ocean. The chief 

 difference between the two is that one is a sea of 

 waters, the other a sea of trees." 1 



It is a very natural inquiry, and one which may be 

 fairly considered as a prelude to a subject such as 

 ours, what number of different kinds, or species, of 

 plants are supposed to be found on the surface of the 

 globe ? This is a question which has been pro- 



1 Hinds hi "Annals of Nat. Hist.," xv. (1845), P- 89. 

 B 2 



