CLASSIFICATION OF SYMBIOTIC PHENOMENA 253 



Symbiotic structures of plants. 



Cecidia (antagonistic symbiosis). 



Zoocecidia (caused by animals). 

 Phytocecidia (caused by plants). 

 Mycocecidia (i.e. Synchytrium). 

 Ph3^cocecidia (cephalodia belong here). 

 Domatia (mutualistic symbiosis). 



Zoodomatia (inhabited by animals). 

 Phytodomatia (inhabited by plants). 

 Mycodomatia (i.e. root tubercles). 

 Phycodomatia (i.e. Azolla). 



This classification, while it served the author's purpose fairly 

 well^ is too incomplete for our present purposes since it leaves 

 disjunctive symbiosis out of consideration entirely and does not 

 offer a satisfactory place even for such things as lichens, the 

 cephalodia, of course, being merely cecidia-like structures occur- 

 ring upon lichens. 



Pfeffer (10) recognizes both conjunctive and disjunctive sym- 

 biosis, but he does not carry the classification further; and the 

 same might be said of several other authors. 



Gager (6) has recently classified symbiotic phenomena as 

 follows : 



1. Disjunctive or social 



A. Nutritive (ants and fungi) 



B. Nonnutritive (insects and pollen) 



2. Epiphytism 



3. Mutualism 



4. Parasitism 



While this classification is broad enough to include most sym- 

 biotic phenomena it appears faulty in certain respects. Polli- 

 nating insects and flowers as an example of non-nutritive disjunc- 

 tive symbiosis does not appear well chosen since in the great 

 majority of cases insects visit flowers for food. The use of the 

 word mutualism should be discontinued, since, so far as known, 

 there do not exist any cases of symbiosis in which two or more 

 symbionts mutually help each other as formerly thought. The 



