XLIX. THE PHENOMENA OF SYMBIOSIS. 



Albert Schne-ider. 



INTRODUCTION. 



All living organisms manifest a more or less intimate biolog- 

 ical interdependence and relationship. In fact, their very ex- 

 istence depends upon this condition; therefore no organism, no 

 matter how simple or how complex its structure may be, is the 

 result of a wholly independent phylogenetic development. 

 Upon careful study and investigation it is found that, although 

 this interrelation and interdependence vary greatly as to 

 quality and quantity, there may be found innumerable inter- 

 mediae phenomena which make it difficult to draw the divid- 

 ing lines. Such a difficulty is, for instance, encountered in 

 attempting to distinguish between mere "associations" or so- 

 cieties (according to Warming and others) and true symbiosis.* 

 Both are evident phenomena of biological interdependence with 

 the general difference that in the former the interdependence 

 is remote, in the latter more close. 



Great difficulty is encountered in limiting and defining the 

 biological relationships in the animal kingdom. Highly auto- 

 mobile organisms do not permit the ready establishment of 

 symbiotic relationships as we have come to understand them. 

 Symbiosis presupposes a certain relative fixedness of the or- 

 ganisms. Thus it is that we may find clearly defined symbioses 

 between highly automobile organisms and those which are com- 

 paratively non-motile. Here it is very essential to keep dis- 

 tinct the difference between auto-mobility and passive motility 

 (immobility). The former tends to counteract or reduce the 

 occurrence of symbiosis; the latter favors its occurrence as 

 well as its modification, as will be explained later in the dis- 

 cussion. The most clearly defined and most highly specialized 

 forms of symbiosis occur between non- motile organisms. 



* The term is used throughout In its broader meaning, not in the sense of De Bary. 



