936 MINNESOTA BOTANICAL STUDIES. 



ally recognized by authors. The latter is more commonly 

 known as parasitism. There are no objections to the use of 

 the term parasitism, since it has become clearly defined and 

 definitely restricted in its application. It is, however, recom- 

 mended that the term antagonistic symbiosis be substituted for 

 the sake of uniformity in terminology. 



From the nature of things the morpho-physiological special- 

 izations and adaptations of antagonistic symbiosis are limited. 

 Although one of the symbionts may be highly benefitted the 

 other is always injuriously affected. This injurious effect may 

 finally reach the stage where it will react upon the parasite, 

 thus indirectly resulting in the mutual destruction of the sym- 

 bionts. In far the greater number of instances the host is not 

 destroyed, nor even seriously injured, although its morpho- 

 logical changes tend in that direction; a condition which will 

 of necessity react upon the parasite. Prom this it also be- 

 comes 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 de- 

 structive 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 symbioses which were origin- 

 ally antagonistic may be subsequently converted into mutualistic 

 symbiosis. Reinke expresses the opinion that the lichen proto- 

 type was the result of the parasitic association of a fungus and 

 an alga (Nbstoc). This transition from antagonism to mutual- 

 ism, however, takes place early in the phylogeny of the sym- 

 biosis. 



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 an- 

 tagonistic 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. The yeast-plant was no doubt originally a 

 green alga. Whether the majority of the bacteria are also de- 

 rived from algae is still is dispute. 



