6 PLANT SOCIOLOGY 



Warming-Graebner (1918), on the other hand, considers the rela- 

 tion of alga and lichen fungus as "helotism." The alga by its chloro- 

 phyll provides carbohydrate nutrients ; the fungus, the rest. The alga 

 does not need the fungus at all but is held in slavery by it. And yet 

 by this union there is formed a new organism wholly self-sufficient, 

 from the standpoint of competition, and one with a specific ecology. 

 The original individualities of fungus and alga are lost and merged in a 

 new and more aggressive organism, so that the term helotism does not 

 seem any more fortunate than the term mutual parasitism. 



Fig. 1. — Symbiosis in the Tamarix coastal forest at Oum er Rebia, Morocco. 

 Cynomorium coccineum, a root parasite, Lonicera hiflora, a liana, and Ephedra. {Photo 

 by Hoffmann-Grohcty.) 



Mycorhizal fungi present undoubted cases of mutual symbiosis 

 (Melin, 1923), wherein the higher plant serves as host and the root 

 fungus as feeder. The union benefits both symbionts, and in spite of 

 their antagonistic relation they form a double organism which thrives 

 better as a unit than either symbiont does by itself alone. 



Epiphytes are less closely related to the host plant. They receive 

 no nourishment from the latter and use it solely as a substratum. By 

 their abundance they may, however, injure the host. In cold and 

 temperate climates epiphytes are without exception algae, mosses, and 

 lichens, but in warm, moist regions ferns and seed plants also grow 



