88 COMMUNAL LIFE OF ORGANISMS sect, n 



The bond between epiphyte and the species upon which it rests is 

 usually less close than in the preceding cases ; most epiphytes can grow 

 upon various kinds of plants, some even upon rock or on the ground. 

 Yet some are confined to definite species, because the nature of the cortex 

 of the latter is of importance. There are epiphytes on aquatic as well 

 as on terrestrial plants. Many kinds of algae live on other algae, or even 

 on phanerogams, and some algae only upon quite definite species for 

 instance, Elachista fucicola on Fucus, E. scutulata on Himanthalia 

 lorea.i 



Epiphytes upon terrestrial plants thrive best where atmospheric 

 humidity and precipitations are rich. Yet a change of seasons, and 

 movements of the air, seem to promote their welfare. Meyen (1836) 

 devoted attention to this subject, and subsequently A. F. W. Schimper 

 dealt with it in greater detail in his papers upon epiphytes.^ In cold and 

 temperate climes epiphytes mostly belong to algae, lichens, and mosses ; 

 but in warm countries they also include a number of ferns and phanerogams 

 (Orchidaceae, Araceae, Bromeliaceae, Cactaceae, Piperaceae, and others) ; 

 and in moist tropical forests there are many epiphyllous species of algae 

 and lichens living upon leaves.^ 



Peculiarities in the habitat have resulted in a number of biological 

 adaptations, which Schimper, Gobel, Raciborski, Mez, Treub, Karsten, 

 and Beccari have explained in reference to flowering plants. The 

 particular details in question are described in the succeeding paragraphs. 



The seeds (and spores) are calculated to gain double object dispersal 

 and fixation to the substratum. Either they are scattered by wind, in 

 which case they are so small and light, or are so provided with long hairs 

 (and the like), as to be easily conveyed by the wind on to trunks and 

 branches where they encounter a fissure or some other depression in 

 which they can become firmly lodged. Or the seeds are contained in fleshy 

 fruits (e. g. Araceae, Bromeliaceae, and Cactaceae) which are eaten by 

 birds, in whose excrement they are dispersed and fastened on to branches. 

 An entirely exceptional method of multiplication characterizes the rootless 

 Tillandsia usneoides, detached fragments of which easily become twisted 

 round twigs of trees by means of their long slender shoots. 



Fixation of the epiphyte to parts of plants is accomplished either 

 by rhizoids (as in the case of mosses and hchens) which penetrate the 

 substratum (dead cortex) to some extent, or by attaching-roots which 

 are irritable and sometimes adhere firmly to the substratum with the 

 aid of fixing-hairs and secretions. There is often a division of labour 

 between attaching-roots and absorbing-roots. 



Provision of water is a problem of difficulty to the epiphyte, because 

 rain-water soon flows away. Some epiphytes obtain the necessary 

 water rather from dew and mist than from rain ; others do the converse.* 

 Many are able to seize the momentary opportunity, and in their dry 

 condition can instantly absorb moisture over their whole surface, e. g. 

 algae, mosses, lichens, Tillandsia usneoides and other Bromehaceae 



^ Concerning the significance attached by Fritsch to the term ' consortium ', 

 see Fritsch, 1906. 



* A. F. W. Schimper, 1884, 1888 ; compare also Mez, 1904 a. 



* Gobel, 1889-92; Raciborski, 1 898 ; Mez, 1904 a; G. Karsten, 1894; Treub, 1888. 

 C. Jennings. * Mez, 1904 a. 



