490 X. GENERAL REMARKS. 



These nos. appear to indicate a rise again of this order in 

 the uppermost zone. But in the two uppermost zones it 

 is rej)resented only bj' a single species, Thymus Serpyllum 

 or Cliameeclrys ; and as the orders are much fewer in the 

 superarctic zone, those of single species will unavoidably 

 be placed higher there than are orders of single species 

 in zones with a longer list ; as is the case with the mid- 

 arctic, which contains an excess of fifteen orders over the 

 superarctic. 



Composite^ keep the first place through all the six 

 zones. But they are equalled by the Gramina in the 

 lowest. And perhaps they maintain the first position in the 

 arctic region onlj' through an over-estimate of the species 

 of Hieracium. Such, at any rate, would be the view in 

 accordance with Bentham's Handbook ; in which the 

 alpine segregate species are re-combined into a single 

 aggi'egate species, H. alpinum. Regarding the orders 

 collectively, they are apportioned among the six zones 



thus : — 



Inferagiarian, 



Midagrarian, 



Superagrarian, 



luferarciic, 



Midarctic, 



Superarctic, 



Among the 55 orders of the 

 yet that 23 are represented there by only single species 

 each. These are to be balanced against 17 so represented 

 in the midarctic, and 14 in the superarctic. In the agra- 

 rian zones, we find the corresponding number of orders 

 of one species each to be, 19 in the inferagrarian, 21 in 

 the midagrarian, 20 in the superagrarian. So that, taking 

 into account the more numerous orders of the agrarian 

 zones, the representation by single species only is much 

 in excess in the arctic zones. And thus again, as 



