EPIPHYTES AND PARASITES 



taken if we conclude that these conditions are those which account 

 for the presence of the hanas. The intenser Hght, uniformly distri- 

 buted at all levels, and the sparser foliage of the trees, favour the 

 growth of the epiphytes. The botanist Schimper tells us that the 

 dense-foliaged trees of the Brazihan campos have no epiphytes, and 

 that the thinner the foliage of the trees, the more numerous are their 

 epiphytic guests. 



Another condition for the growth of arboreal vegetation is humidity 

 of the atmosphere and frequent rainfall. Since the epiphytes grow 

 high up on the boughs they cannot absorb the moisture of the soil. 

 Consequently the greatest number of epiphytes are found on the 

 slopes of the mountains, on which the passing clouds shed their 

 moisture, or in valleys where the air is constantly humid. In Ceylon 

 I found the greatest number of epiphytes on the south-western 

 slopes of the central range, where it rains every day about noon. 

 In Brazil too the rain-forest of the coast contains many epiphytes, 

 whereas in the dry regions of the wilderness the boughs of the trees 

 are generally bare. Winter is of course a hindrance to the develop- 

 ment of epiphytes. Many of our European plants survive the winter 

 although the plants themselves die down, but then the roots retain 

 their vitahty in the warm earth. On the boughs of the trees the roots 

 would be exposed without means of defence to the storms and frosts 

 of winter. But if the epiphyte wished to become an "annual" — that 

 is, if it intended to die every autumn and leave only its seed to 

 survive the winter — this seed would have to remain on the tree for 

 more than a year, enduring wind and rain and snow, and to resist 

 the efforts of the rain to wash it away. 



Lastly, the epiphytes must find suitable lodgments on the boughs. 

 Such lodgments are more abundant in the tropical forest than in 

 our northern woods, for the boughs are more massive and more 

 numerous ; moreover, they often bend sharply upwards, and develop 

 rugosities, and the constant humidity leads to the formation of 

 chinks full of vegetable mould. Many trees, like the fig-tree, extend 

 their boughs for yards in a horizontal direction, supporting them 

 by means of aerial roots ; and the horizontal spans of the lianas 

 afford a suitable lodgment, as do the spiral twists of their shoots. 

 The tropical forest is a scaffolding, and a scaffolding naturally affords 

 many places of lodgment. 



But the plants which adopt the life of epiphytes must adapt them- 

 selves to these conditions. Since all things living evolve, we must 

 suppose that even the epiphytes were once terrestrial plants, as many 



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