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, Ericacece), 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- 



2D 



