Sept.. 1893. ON EPIPHYTES. 173 



constituted so as to avoid too rapid transpiration (succulence or 

 leathery or hairy nature, strongly developed epidermis with thick 

 cuticle, water-storing tissue) (i). A plant evolved so as to suit 

 one of the above-mentioned environments would incidentally become 

 suited to one of the other modes of life ; and it might desert its old 

 habitat and take up the new one for which it had casually become 

 suited. This process has taken place ; even now we find plants of 

 which some individuals are epiphytic in jungles, and others are terrestrial 

 alpine plants. In other species, some of the individuals are littoral plants, 

 which do not reappear inland until we reach the mountain tops ; and 

 what is true of these individuals is true of certain species of genera. 

 The genus Casuarina is a littoral form and a Malayan alpine form, but 

 does not occur in the jungles between these two extremes. So it 

 becomes very difficult to say what characters in a plant are truly 

 adaptive, i.e., acquired with special reference to the present mode of 

 life. And we can only solve the mystery in each case by, on the one 

 hand, studying the physiological nature of the plant ; and, on the other, 

 tracing out its past history by means of morphological comparisons 

 with allied forms, and observations on the geographical distribution of 

 it and its relatives. The first person to recognise this was A. F. W. 

 Schimper, whose work on tropical American Epiphytes (2) revolu- 

 tionised this branch of botany. He introduced a new method of 

 treating biological problems, which should serve as a model for 

 subsequent investigators. 



Epiphytes are subjects peculiarly suitable for the study of adapta- 

 tion ; for among them occur all stages from unmodified terrestrial 

 plants right up to forms highly metamorphosed to suit their aerial 

 mode of existence. 



For our knowledge on Epiphytes we are almost solely indebted to 

 Schimper, and the present article is almost entirely based upon his 

 work. Goebel, however, who has followed — far behind — in 

 Schimper's footsteps the study of the biological problems, has been 

 at the trouble to collect facts observed by other investigators of 

 Epiphytes, and has added a few examples illustrating the principles 

 advanced by Schimper and others (3). 



Compared with temperate forests, the moist tropical jungles are 

 overwhelmingly rich in Epiphytes. There they vary in size from 

 minute epiphyllous lichens up to the gigantic herbs or huge shrubs. 

 Often an Epiphyte is itself loaded by countless others, on which, in 

 turn, are crowds of smaller ones. 



Most of these are confined to a few families : — Lycopodiacea, 

 Ferns, Bromeliaceae, Araceae, Orchidaceae, Urticaceae, Piperaceae, 

 Melastomaceas, Ericaceae, Asclepiadaceae, Solanaceae, Gesneraceae, 

 and Rubiaceae (as well as our temperate Epiphytes, Mosses, and 

 Lichens). Although these families are few in number, they contain 

 many epiphytic genera ; and, with the exception of the purely 

 American family, the Bromeliaceae, they occur in the tropics of both 



