THE FLORA 399 
whereby the leaflets may open out in moderate illumina- 
tion and close together under conditions where transpira- 
tion tends to be excessive, in strong wind or hot sun. 
Another device consists in folding back the edges of the 
leaves underneath (Cassiope tetragona, Ledum, Pinguicula) ; 
and still another, in crowding them thickly together (Cas- 
siope, Bryanthus). All of these many modifications have 
the one object of securing a reduced or reducible transpir- 
ing surface, and almost all the plants of Labrador adopt 
one or another of these methods of accomplishing it. The 
examples given are only illustrative, and might be increased 
many fold under almost every heading. 
4. Increase in thickness of the leaf and of its cuticle. 
Many leaves are tough and leathery (Hricacew, Empetrum) ; 
or have thick, strong cuticle (grasses and sedges) ; or develop 
a waxy, resinous, or varnished coating on the under side 
or on both (Andromeda, Vaccinium Vitis-Idea, Pyrola, 
some Salices, evergreens). 
5. Development of water-storing cells in stem or leaves, 
the latter becoming thick and succulent. This is not of 
very common occurrence. It is found, however, for ex- 
ample, in saxifrages, Sedum, and Sphagnum. 
6. Protection of the stomata from the influences that 
tend to cause evaporation through them. This may be 
secured by (1) turning away the under side of the leaf from 
sun and wind, as in the pinnately divided leaves men- 
tioned already; (2) sinking the stomata in the leaf-surface 
(Andromeda, Empetrum); (3) covering the under side of 
the leaf and sometimes also its upper side and the stem with 
a protecting layer of hairs or tomentum, which may vary 
greatly in length and thickness, from a mere silvery or 
