THE CLASSIFICATION OF SYMBIOTIC PHENOMENA 



W. B. McDOUGALL 



University of Illinois, Urbana, Illinois 



Biotic factors have received much less attention from modern 

 ecological workers than they deserve. One result of this is a 

 lack of any general agreement concerning the status of certain 

 common phenomena and concerning the meaning and scope of 

 certain concepts or terms. One of the terms whose scope and 

 definition varies greatly with different writers is symbiosis. 

 This word is defined in text books in a great variety of ways 

 ranging from a very narrow sense to the broadest possible in- 

 terpretation. That this is true is evidenced by the following 

 quotations taken somewhat at random from authors whose 

 books are available to every one. 



Campbell (2) states that ''a special form of parasitism called 

 symbiosis is exhibited by some fungi" and cites Hchens and myco- 

 rhizas as examples. This is probably the narrowest sense in 

 which the term will be found defined, since it is made subordinate 

 to parasitism, though probably Campbell's conception of symbiosis 

 is not different from that of numerous other authors. 



Ganong (7), writing of mycorhizas, says: ''And accordingly 

 we have here one of the cases where two different organisms de- 

 rive benefit from their association, a condition called symbiosis." 

 The further discussion by Ganong shows that he interprets this 

 definition in a very limited sense. 



Curtis (4), also writing of mycorhizas, tells us that "this state 

 where two or more plants live together is termed symbiosis." 

 This sounds like a broad definition but the interpretation of it 

 by Curtis limits it to such classical examples as lichens and 

 mycorhizas. 



Harshberger (8) says: ''Some fungi are symbiotic, that is, 

 they are found in intimate relation with chlorophyll-containing 



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