252 W. B. McDOUGALL 



Bary's idea of symbiosis, how has the definition become so 

 Hmited in the minds of many modern writers? Perhaps it is 

 useless to speculate on this question but it may have come about 

 in the following way. 



The paper by De Bary, from which the above quotations were 

 taken, was published as a separate and is not found in many 

 libraries. Probably, therefore, many of the modern writers have 

 never seen the original article. Several pages in this article 

 are devoted to the relation between fungi and algae in lichens. 

 The knowledge of this relation was new at that time and for 

 that reason this part of the paper attracted most attention and 

 was most emphasized by those who later had occasion to refer 

 to the publication. Jost (12), for instance, makes the state- 

 ment that De Bary first used the word symbiosis in connection 

 with lichens. Now the relationship between fungi and algae in 

 lichens was thought to be unique and entirely different from para- 

 sitism. It was a fine thing to talk about to students. It was 

 only natural, therefore, that symbiosis should come to mean in 

 the minds of many only that supposedly unique sort of relation- 

 ship represented by lichens. 



At present, of course, it is well known that the interrelation 

 between lichen-fungi and algae is not essentially different from 

 ordinary parasitism. It is merely what has been called recipro- 

 cal parasitism in which each organism is a partial parasite on the 

 other. Therefore we would have no need at all of such a word 

 as symbiosis if we were to limit it to the few known cases of 

 reciprocal parasitism. It is a very handy word, however, 

 when employed in the sense in which De Bary used it and should 

 by all means be retained with that meaning. 



There have been but few attempts to classify the phenomena 

 that should be included under symbiosis. De Bary (5) himself 

 mentioned various types of symbiosis but he did not elaborate 

 upon their classification. Lundstrom (9), classifies symbiotic 

 plant structures as follows: 



