SYMBIOLOGY THE BIOLOGICAL RELATIONSHIPS OF ORGANISMS 147 



stroyed, nor even seriously injured, although its morphological changes 

 tend in that direction; a condition which will of necessity react upon the 

 parasite. From this it also becomes evident that it is desirable for the 

 parasite to locate upon a host whose vitality and biological activities are 

 many times greater than its own. This we find to be the case, the host 

 is quite generally a large plant, while its parasites are comparatively 

 small. 



Strictly speaking, antagonistic symbiosis is therefore a destructive 

 association. The morphological and physiological changes tend toward 

 dissolution rather than evolution. It is a change from the higher to the 

 lower, hence a katabolic change. There is, however, no doubt that sym- 

 bioses which were originally antagonistic may subsequently be converted 

 into mutualistic symbiosis. Reinke expresses the opinion that the lichen 

 prototype was the result of the parasitic association of a fungus and an 

 alga(Nostoc). This transition from antagonism to mutualism, however, 

 takes place early in the phylogeny of the symbiosis. 



As has already been indicated, the majority of symbioses were perhaps 

 originally more or less antagonistic, although actual experiments are 

 wanting to prove this. Incipient antagonistic symbioses are, however, in 

 existence, represented by some Chlorophyceae and Cyanophyceae,in and 

 upon higher plants. In time these algae will no doubt lose their chloro- 

 phyllian function and depend entirely upon the organic food supply of 

 the host. 



i. Mutual Antagonistic Symbiosis (Mutual Parasitism). Mutual 

 parasitism as such has heretofore received little or no recognition. 

 It is a phenomenon characterized by the mutual antagonism of the 

 symbionts and is therefore essentially different from antagonistic 

 symbiosis proper, or parasitism. It is a relationship which can not 

 readily occur. If, for example, two or more symbionts nearly equal 

 in size and in vitality, enter into a relationship of mutual antagonism 

 two things may occur. Owing to the antagonism a prolonged sym- 

 biosis is impossible, and the symbionts will return to the original 

 substrata, or they will mutually destroy each other. It is, however, 

 highly probable that an association of organisms, which was at first 

 more or less mutually antagonistic, later developed into antagonistic 

 symbiosis proper or even into mutualistic symbiosis. As an illustra- 

 tion of mutual antagonistic symbiosis, we may mention the cells of 

 any pathologic growth, as carcinoma, epithelioma, etc. The cells com- 

 posing the growth are antagonistic toward each other, as well as toward 

 the normal cells of the organism upon which they occur. This antago- 

 nistic relationship of the tumor forming cells is indicated by the fact that 

 they are much weakened in comparison with the normal body cells. In 



