342 WHERE KNOWLEDGE TERMINATES. 



Arabia are still sealed letters, treasuries to which we have 

 not found the key. As much may be said of the floras of 

 the countries situated between the Thian-Schan, the Kuen- 

 lung, and the Himalaya, as well as of the floras of western 

 China, and most of the trans-Gangetic countries. We know 

 still less of the vegetation of the interior of Madagascar, 

 Borneo, New Guinea, and the greater part of Australia. To con- 

 clude : we are probably not acquainted with more than one-fifth 

 of the vegetable species which cover the surface of our globe. 

 There are regions, moreover, which we imagine will always 

 lie outside of our sphere of investigation ; such, for instance, 

 are the Polar regions, properly so called. Undoubtedly, it 

 is open to us to conjecture that the Poles those two extremi- 

 ties of our axis of planetary rotation are not the home of 

 any form of life. But this is only a conjecture ; we are even 

 without an analogy for it; since we have found, as shown 

 in an earlier chapter of the present volume, living beings, 

 plants, and animals, among the snows of our loftiest moun- 

 tains. Moreover, might not the auroras, whose maximum of 

 intensity occurs exactly at the poles, render life possible in 

 regions where we at present suppose it to be /^possible ? Con- 

 jecture for conjecture, acknowledge that we here touch in both 

 cases upon an element completely beyond our human power. 



These, then, are the reasons why, at present, we can only 

 venture upon defining the lower limit, the restricted number, 

 above which we are unable to fix the total of vegetable species 

 living on the surface of our planet. 



