224 ROUND THE YEAR 



distribution of these plants outside the British Isles. 

 A little inquiry brings to light the fact that the Ling, 

 Bilberry, Cranberry, Cowberry, Andromeda, Crow- 

 berry, together with the commonest moorland grasses, 

 all extend far into the Arctic Circle, the Scotch Heath 

 and the Cross-leaved Heath close up to it. The 

 defences of which they mainly stand in need are 

 defences against Arctic and Alpine cold, but these 

 are effective also against the drought of an English 

 summer. Drought and cold and wind all tend to parch 

 the tissues or at least to cut off the supply of water 

 taken in by the roots, and diminished transpiration is 

 the remedy of nature for all three contingencies. 



To make this clearer I will enumerate the defences 

 of desert plants against extreme drought, and append 

 to each a short list of Arctic, or at least high northern 

 plants which exhibit the same feature. 



Xerophilous or desert plants often exhibit one or 

 more of the following features : 



1. The leaves are reduced, rudimentary, or wanting 

 altogether. Among Arctic or high northern plants 

 various species of Juncus (Rush) yield examples of 

 the same thing. Furze (which, however, is not 

 Arctic) has trefoil leaves as a seedling, which are 

 afterwards replaced by spines, which contain chloro- 

 phyll and possess stomates. Pines, Juniper and many 

 Heaths have the leaves much reduced in size. 



2. The leaves are rolled up. Crowberry, etc., are 

 Arctic examples. 



3. The leaves are closely imbricate, or pressed against 

 the stem, or pressed against the ground, in the last 

 case usually forming rosettes. All these arrangements 



