THE ALPENROSES 25 



new leaves of the current year at the tips of the 

 branches are green beneath. There are also no hairs 

 in this species on the edges of the leaf. 



The Hairy Alpenrose, Rhododendron hirsvium, 

 Linn., is more common on limestone soils. At one 

 time it was believed to be entirely confined to 

 calcareous rocks, but it is now known that this is not 

 the case (p. 117). This shrub is very similar in appear- 

 ance to the Common Alpenrose, but all the leaves 

 are green beneath, and are fringed with hairs along 

 their margins. In both, the numerous stem branches 

 are bare of leaves except near the tips. 



There is nothing of much interest to add as 

 regards the flowers of the Alpenroses. But the 

 leaves of both species are specially protected, as in the 

 case of the Edelweiss, against excessive evaporation 

 (transpiration; see p. 12), though here in quite a 

 different way and in a less marked degree. The 

 leaves of all members of the Heath family (Ericaceae) 

 are evergreen — that is to say, they are not all shed at 

 once in autumn, but new leaves gradually replace the 

 old ones, which last in the case of the Alpenroses 

 from three to four years, so that the shrubs are 

 never leafless even in winter. The great majority 

 also show some adaptation against excessive transpira- 

 tion, though form of the adaptation varies greatly in 

 different cases. 



In the Common Alpenrose the rusty-brown colour 

 of the under-side of the older leaves is the outward 

 and visible sign of the means whereby excessive 



