66 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



While it might be true that some symbiotic complexes 

 may have arisen in this manner, there is no evidence at 

 hand to indicate that this is the usual manner of develop- 

 ment of symbiotic complexes. On the basis of our knowl- 

 edge of microbial behavior, we must admit that there exists 

 a wide range of reactions of Uving organisms to each other. 

 We are justified in concluding that in many instances the 

 physico-chemical properties of the symbionts entering into 

 a relationship are of such a nature that the terms ''parasi- 

 tism," ''infection" and "disease," as they are commonly 

 understood, could not be apphed to the relationship. 



The evidence for and the nature of the development of 

 symbiotic complexes are discussed at more length in the 

 chapters following. 



