CHAPTER IV — SAPROPHYTISM AND SYMBIOSIS 

 I. COMMENSALISM AND SAPROPHYTISM 



Symbiosis and related phenomena. — Autophytes and heterophytes. — 

 The preceding sections have been devoted to a detailed consideration of 

 the ecological aspects of nutrition in green plants. Such plants may be 

 termed aiUophytes, autotrophic plants, or independent plants, because 

 they are able to obtain all necessary food materials directly from inorganic 

 sources, subsequently converting them into foods. In striking contrast 

 thereto are the heterophytes, heterotrophic plants, or dependent plants, 

 whose existence depends upon antecedent or coexistent organic forms, 

 because they derive at least a part of their food from organic sources. 

 Since the nutritive relations of the heterophytes are so different from 

 those of the autophytes, they are made the subject of a separate chapter. 

 Heterophytes may be subdivided into saprophytes, which obtain food 

 from dead organic matter, and parasites, which obtain food or food 

 materials from living organisms. 



Symbiosis. — When two or more diverse organisms live together in 

 more or less intimate relationship, the phenomenon is termed symbiosis, 

 and the individual organisms are termed symbionts. The phenomena 

 included in symbiosis may be conveniently grouped under the subheads, 

 parasitism and commensalism.' Parasitism is that form of symbiosis 

 in which one organism, thp parasite, derives food or food materials from 

 another, the host, manifestly to the detriment of the latter; sometimes 

 each symbiont derives food from the other (as in the case of clover and 

 bacteria), a relationship that may be termed reciprocal parasitism. Com-- 

 mensalism includes those cases of symbiosis in which two or more organ- 

 isms live together vnth possible benefit to some or all of the symbionts, 

 but with injury to none. The individuals in commensalistic symbiosis 

 are termed commensals. Dependent and interrelated plants thus may be 

 divide'd into three classes: commensals, which are symbiotic but not 

 inecessarily heterotrophic; saprophytes, which are heterotrophic but 



' Saprophytism, of course, is not included under symbiosis, since it does not involve 

 a relationship between living organisms. 



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