CHAPTER V 



SY^IBIOSIS-DISJUNCTIVE 



Symbiosis means the living together of two or more unhke organ- 

 isms, that is, organisms belonging to more than one species. It 

 includes all such cases. While this is a broader definition than has 

 been used by many authors it is the one that applied when the word 

 was first introduced as a biological term and is considered the only 

 one that is completely satisfactory. Any attempt to limit the defi- 

 nition of symbiosis leads one into the difficulty of trying to recognize 

 lines of division between living phenomena where no lines exist. 

 Hence it is much better to accept the definition as including all cases 

 of the living together of two or more organisms of different species. 



33. The Classification of Symbiotic Phenomena.— The various 

 kinds of phenomena included under the term symbiosis are con- 

 veniently classified as follows: 



I. Disjunctive symbiosis. II. Conjunctive symbiosis 



1. Social 1. Social 



2. Nutritive 2. Nutritive 



(a) Antagonistic (a) Antagonistic 



(a) Reciprocal (b) Reciprocal 



In disjunctive symbiosis the organisms concerned are not in actual 

 contact, at least not all of the time, while in conjunctive symbiosis 

 the symbionts are in actual contact throughout the time during 

 which they are said to be in a state of symbiosis. Social symbiosis, 

 whether disjunctive or conjunctive, includes all cases in which dis- 

 similar organisms are living together but without any direct food 

 relation; that is, none of the symbionts derive food directly from the 

 others. In nutritive symbiosis, on the other hand, one or more of the 

 symbionts derives food directly from one or more of the other sym- 

 bionts. Again, when only one or more but not all of the symbionts 

 derive food from other symbionts, and these latter are in no way 

 benefited but often injured by the relationship, the condition is said 

 to be one of antagonistic nutritive symbiosis, but, when all of the 

 organisms concerned obtain food or some other obvious benefit from 

 the relationship, they are living in reciprocal nutritive symbiosis, 

 either disjunctive or conjunctive. Examples of these various types 



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