926 MINNESOTA BOTANICAL STUDIES. 



ily adapted to form symbiotic relationships; therefore the or- 

 ganisms, during their first contact, had the same relation to 

 each other that they had to their substrata, or more correctly 

 to their entire environment. The changes in the substrata are 

 destructive (disintegrative), due to the food-requiring and re- 

 productive life- action of the organism. The antagonism in the 

 incipient symbiosis is, however, so slight as to be incapable of 

 detection. Subsequently antagonism may be increased or be 

 converted into nutricism or mutualism; this depending largely 

 upon the nature of the symbionts. It becomes very evident 

 that the question of the origin of symbiosis is directly con- 

 cerned with the questions of the "struggle for existence," 

 "survival of the fittest," as well as with the problems of gen- 

 eral evolution. We may cite the case of parasitic fungi for the 

 purpose of explaining the probable origin of antagonistic sym- 

 biosis. Most fungi are, no doubt, derived from algae, as cer- 

 tain morphological similarities would lead us to believe. Owing 

 to lack of space, or over- productiveness, certain algae fre- 

 quently came in contact with more highly organized plants and 

 animals from which they absorbed (by osmotic action) various 

 organic food-substances, thereby reducing the necessary activ- 

 ity of chlorophyllian assimilation. Co-incident with the first 

 contact and resultant change in function, there was a corre- 

 sponding change in structure. As the opportunities for the 

 symbiotic association continued (perhaps more or less inter- 

 ruptedly), the morpho -physiological changes progressed in the 

 direction of parasitism and away from independence. Finally 

 the originally independent chlorophyll-bearing and carbon 

 assimilating organism became wholly dependent upon an or- 

 ganic food-supply and sustained a total loss of the chlorophyl- 

 lian function. There is no doubt that the host plant or host- 

 plants are also more or less affected by the symbiosis. The 

 relative morpho-physiological changes are approximately in 

 proportion to the size (volume) and biological activity of the 

 organisms. 



Above all it is desirable to keep distinct the difference be- 

 tween mere associations and societies of organisms and sym- 

 biosis proper. Unless this is done we shall further complicate 

 a subject which is already very complicated The former condi- 

 tions are of great importance biologically, but the latter attract 

 the most attention at present because of their intimate relation- 

 ship with the well-being of man himself. There is scarcely a 

 problem of economic significance which is not directly con- 



