2 



INTRODUCTION. 



In order to obtain a correct conception of these riches, it is necessary to call 

 to mind the spherical shape of our globe. The different climates and their transi- 

 tions will then be most evident. It is well known that their differences exercise 

 a direct bearing on those of the vegetation ; heat and moisture, the various degrees 

 of which determine climatic differences, also constituting the principal conditions 

 of vegetable life. The greater the harmony in which these two agents act, the 

 grander the result of their co-operation. This is the reason why the lowest lati- 

 tudes, the tropical zones, with exception of their arid deserts, exhibit the greatest 

 force of vegetation, the finest and most diversified forms, and the largest number of 

 species. At every marked approach towards the icy poles, and in proportion as 

 the temperature decreases, the vegetation becomes altered, assuming more and 

 more what has been termed a ec northern look," until it dwindles down to an Alpine 

 flora, and ultimately to a mere crust of lichens covering the rocks. What a variety 

 of features must there be ranged between this extreme and the gigantic forests of 

 the equinoctial regions ! 



As the temperature decreases with the increasing altitude, exactly the same 

 succession is exhibited in the different regions of the higher mountains, where 

 the various forms of vegetation, from those of the temperate zones to the polar, 

 the limits of perpetual snow, are found successively. But, however much diversity 

 there might be in these gigantic terraces, if in every instance the same characters 

 were repeated, interest in them would be much diminished. One would in that case 

 only have to ascend a given mountain, the summit of which reached the region of 

 perpetual snow, in order to behold the vegetation of the cooler regions. A country 

 situated in about latitude 30° south would present as faithful a picture as one 

 situated as far north. This, however, would ill agree with the evident tendency of 

 Nature towards diversity, its manifold variations of certain forms, and the transition 

 to which they give play. Nature has guarded against the forests of the Straits of 

 Maghellan having quite the same aspect as those of Europe. Certain plants of 

 both hemispheres may be similar, but there are specific differences which separate 

 them and render their mutual similarity very slight.* The very different dis- 

 tribution of land and sea hardly produces in corresponding latitudes a sufficient 

 similarity of climate to insure, even in part, a complete identity of species. Expe- 

 rience has also demonstrated how difficult it sometimes is, in attempts at trans- 



* This is not absolutely the case. There is a land ("Botany of the Voyage of H.M. S. Herald," 



number of species which are found wild in both London, 1852-1857, p. 20), and that will no doubt 



the Arctic and the Subantarctic circle. A list of be considerably extended by future researches. 



them was given in my Flora of Western Eskimo- Berthold Seemann. 



