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INTRODUCTION TO PLANT GEOGRAPHY 



[chap. 



heathy or herbaceous vegetation, with ultimately, far above, sparse 

 fell-fields, etc., as described in Chapter XIII. Sometimes, as in 

 the tall mountains of New Guinea, other zones are interpolated. 



In tropical and subtropical regions of dry climate, as in temperate 

 lands, forest (or intermediate savanna, etc.) may appear only in the 

 montane zone — or occasionally not at all, as on the western slopes 

 of the Andes in parts of South America, where scrub, steppes, or 

 arid ' punas ' characterized by large cushion-plants prevail. Near 



P"k;. 163. — Mossy elfin forest near summit of moLintain, Philippine Islands. 

 Trunks, branches, and aerial roots of trees are covered with festoons of Mosses. 



the latitudinal limits of the subtropics, something approaching 

 deciduous summer forest and, above it, forest characterized by 

 evergreen Conifers, may in some places constitute the upper limits 

 of arborescent vegetation and simulate the march into higher 

 latitudes [cf. Fig. 83, B). Details also vary elsewhere in many other 

 ways, such as the altitudinal limits involved, though these last tend 

 to become depressed with increasing latitude, proximity to coasts, 

 or exposure to prevailing winds. However, owing to the ' height ' 

 of the sun and the wide angle of incidence of its downpouring rays, 

 the influence of aspect tends to be far less marked in tropical than 

 in temperate and polar regions. 



