THE FLORA 401 
Such are the main characteristics of xerophytes. They 
constitute the great bulk of the flora of Labrador, since 
almost all its physical conditions — bog, sea-shore, thin 
soil, cold ground, drying winds — are such as to exert a 
xerophilous influence. Hygrophytes (reaching their ex- 
treme in Aquatics), adapted to conditions of easily avail- 
able moisture, and Tropophytes, adapted to alternating 
seasons of moisture and of dryness, are of much rarer 
occurrence. The former are characterized by weakly 
developed roots, more luxuriant vegetal growth, great 
expansion of the transpiring surfaces. Tropophytes are 
hygrophilous during the summer, the season of mois- 
ture, and xerophilous during the winter, which is physio- 
logically dry. They secure this change either by shed- 
ding their hygrophilous leaves; or by dying down to the 
ground as a whole; or, as in evergreens, by developing 
shoots which are hygrophilous only when young, turning 
xerophilous as they mature. 
Thus a relative lack of available moisture is one of the 
chief features determining the general appearance of the 
vegetable covering of the Labrador landscape. Other 
factors, such as cold, wind, and physical nature of the soil, 
derive their influence mainly from their tendency to limit 
the supply of available water, or to increase transpiration. 
Each of them, however, has some direct influence besides. 
Thus it is said that cold tends to make leaves broader and 
shorter, with bent margins and loss of irregularity in mar- 
gin (mosses, Hricacew), and is favourable to the develop- 
ment of sexual organs; though the real influence even here 
may be perhaps not cold directly, but dryness and the short- 
ness of the season of growth. Wind not only favours trans- 
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