Chap. II] GUILDS i 99 



Asclepiadaceae, Gesneraceae, and Rubiaceae. Moreover, from the first all 

 plants that produce many lateral roots and require relatively little water 

 gain an advantage. Hence the number of species that could emigrate to 

 trees was relatively small, and victory over competitors was dependent on 

 conditions other than those prevailing on the ground. 



In those species which no longer grew on the ground and therefore could 

 persist as epiphytes only, those characters were naturally selected that were 

 specially suited for existence on trees ; they have been adapted to this. 

 Especially was every characteristic that enabled an epiphyte to advance 

 upwards towards the light preserved and further developed. In the first 

 place, in this relation protective means against the loss of water are in 

 question, for every step on the way from the base to the summit of a tree 

 brings with it not only more light but also greater dryness. Epiphytes 

 growing at the base of trees in a rain-forest are hygrophilous, those that 

 occur on the highest branches are xerophilous. The whole matter gives 

 the impression of a gradual ascent from the deep shade into the sunlight, 

 from the damp cool air of the interior of the forest to the dry heat of the 

 top of the forest. 



Xerophilous sun-loving epiphytes of the summits of trees, although they 

 represent the descendants of hygrophilous shade-bearing plants, are able 

 to desert the rain-forest. Thanks to their changed characters they are 

 able to inhabit quite open country. Thus they emigrated from the rain- 

 forests, and colonized regions with markedly dry seasons, especially 

 monsoon-forests, savannahs, and savannah-forests. A limit was set to 

 their success only where the drought lasted several months without being 

 interrupted regularly by heavy falls of dew ; yet there they were able to 

 settle permanently on the banks of rivers and lakes. The winter cold 

 more completely arrested the emigration of tropical epiphytes. Only few 

 species endowed with specially strong powers of resisting drought and 

 cold, such as Tillandsia usneoides and Polypodium incanum in North 

 America, were able to advance into districts with cold winters. 



The tropical rain-forests have been by far the most important sources of 

 origin of the epiphytic guild, and their productions have penetrated far 

 into the warm temperate zones of North America, Argentina, Japan, and 

 Australia. We also find, however, in the temperate zones two limited 

 autochthonous sources of origin of higher epiphytes, namely, in the com- 

 paratively inextensive temperate rain-forests of Southern Chili and of 

 New Zealand. Here real temperate higher epiphytes have sprung from 

 temperate phanerogams and ferns. 



Outside this region, as autochthonous epiphytes, we find only small Algae, 

 lichens, and mosses, that is to say, plants that, owing to their faculty of 

 existing for months in a dry condition, can resist even the desiccating 

 effects of prolonged winter cold. But even they are found richly developed 



