THE FACTORS OF DISTRIBUTION 35 



fleshy leaves closely pressed upon the ground are adapta- 

 tions to the economy of heat. The dense covering of 

 hair in the Edelweiss or on many buds, and the persisting 

 dead leaves of arctic and alpine plants, are explained as 

 a non-conducting protection against rapid freezing or 

 thawing and excessive transpiration. 



Internally, the same condition seems to determine: 



(i.) The secretion of fat instead of starch, and, perhaps, 

 that of resin; 



(ii.) The development of the red or purple anthocyan 

 in lieu of chlorophyll in grasses near the snow-line, and 

 in plants in dense shade, transforming light-rays into 

 heat; and 



(iii.) The formation of wood, as in alpine undershrubs, 

 or other dry structures, such as those of mosses and 

 lichens, which are better able to resist cold than succulent 

 structures. 



What is usually miscalled acclimatisation is merely 

 the introduction of species from climates as nearly 

 identical as possible with that of the land to which they 

 are brought. Very little can apparently be done to 

 acclimatise a plant to a climate other than its own. 

 What does seem possible in this direction is to secure the 

 healthy if somewhat more rapid growth of broad- 

 leaved trees in a climate slightly warmer than that to 

 which they are native. 



C. ATMOSPHERIC MOISTURE 



No active life is possible in the absence of water. It 

 is essential to germination, is itself an important food- 

 material, and acts as a solvent for all the mineral 

 food-materials, and as a vehicle for the absorption and 

 transference throughout the plant of all food -materials 

 and foods. The physiological activity of protoplasm is 

 checked unless it is saturated; that of the entire cell 

 unless it is maintained by such saturation in a state of 

 turgor; and accordingly the opening of the stomata, 

 which permits transpiration, does not take place when 

 the supply of water is absent. 



Some cryptogams, such as lichens, some mosses and 

 Selaginellas, and parts of some of the higher plants can, 

 however, remain in a state of suspended vitality when 

 almost completely desiccated. 



