28 



BRITISH FLOWERING PLANTS 



hand, equally necessary that it should not be too rapid, 

 for in severe weather the frost often checks the supply 

 of water by the roots, even though they go to a con- 

 siderable depth. 



The same safeguards against too rapid evaporation 

 render them suitable to hot dry regions. The leatheri- 

 ness of the leaves is also, no doubt, a protection against 

 browsing quadrupeds, as also are the aromatic properties 

 of many such species. Besides the Heaths, Azalea, 

 Empetrum (Fig. 11), Silene acaulis, and some Saxi- 

 frages belong to this type. 



Another northern type is that represented by 



Fio. 11. — Transverse section of leaf of Empetrum. u;, upper face ; 5, under face ; 

 «■, stoma, shown closed by the approximation of the guard-cells. 



Cerastimn alpinwn. The tapering form carries off 

 the moisture, which, moreover, is kept from the stomata 

 by matted woolly hairs. The result is that as soon as 

 the sun comes out transpiration becomes possible. On 

 the other hand, they are less suitable where there is 

 much snow. 



Other leaves of the same type are Salix lanata and 

 S. repens (two of the Arctic Willows), Gnaplialium 

 sivpinum (Arctic or Dwarf Cudweed), Bartsia alpina, 

 the Mountain Forget-me-not (Myosotis silvatica), 

 Cotoneaster vulgaris, and Hieracium Pilosella, one 

 of our commonest Hawkweeds. 



Another type may be called " snow leaves." Of this 

 group Viola palustris is an example. The leaves seem 



