62 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



Since the observations of Reinke and De Bary, the num- 

 ber of recorded cases of symbiosis has steadily grown. In 

 most cases of symbiosis early described the two symbionts 

 were multicellular plants or animals. It is perhaps be- 

 cause of this circumstance that symbiosis has been looked 

 upon more or less as a digression in plant and animal behav- 

 ior. That symbiosis may represent the end result of a 

 biological principle appears to have escaped detection. 

 The kind of symbiosis in which one symbiont is a micro- 

 organism is not so well known. It is this type of symbiosis, 

 which we designate "microsymbiosis," that is of particular 

 significance in the theory of Symbionticism. 



Various classifications of symbiosis have been devised 

 by different authors. These have been based for the most 

 part upon the physiological responses of multi-cellular 

 symbionts. While such classifications may be valuable 

 from one point of view, they are of httle significance in 

 connection with prototaxis. Based upon the morpholgic 

 relationship of the symbionts, symbiosis may be divided 

 into intracellular and extracellular types. Symbiosis may 

 be incomplete or absolute (facultative or obligate) de- 

 pending upon the degree of physiological dependence of 

 the two symbionts. In incomplete symbiosis, the two 

 symbionts are capable of more or less independent existence 

 and reproduction. In absolute symbiosis, they are incapa- 

 ble of independent existence and reproduction. In this 

 grouping the author has particular reference to microsym- 

 biosis. It might be well to use the term "macrosymbiosis" 

 to designate that type of association in which the two 

 symbionts are multicellular organisms. In macrosymbio- 

 sis, the two symbionts are not so intimately associated, 

 and appear to have httle or no significance in the modifi- 

 cation of species. 



The term "symbiosis" is used in bacteriology in a differ- 

 ent sense than in general biology. Certain bacteria, ap- 



