104 COACTION: THE INTERRELATIONS OF ORGANISMS 



the characteristic process in the plant matrix. Thus, in the study of 

 the biotic community as distinguished from that of separate plant or 

 animal communities, coaction is commonly a paramount theme, though 

 it is regularly to be considered in proper relation to other community 

 functions. 



BASES OF COACTION 



Organisms. In its simplest form, each coaction comprises the 

 reciprocal behavior of two individuals of the same or different species ; 

 the more complex coactions involve the interaction of one group or 

 community with another. These may consist of plants or animals 

 alone, or more rarely of both acting together. In the main, the gen- 

 eral nature of each particular coaction is determined by the life form 

 and life habit of the species concerned. The specific quality of this 

 relation is usually derived from behaviors common to families, or 

 genera of animals ; this is frequently true of plants also, but only when 

 life form and taxonomic form are in accord. 



It is the exception that the organisms concerned in a coaction 

 play equal or similar roles, though this may frequently be true of 

 social interrelations. As between animals and plants especially, the 

 former are largely active, the latter passive. The difference is usually 

 one of motility, though not necessarily so, unless to this is assigned 

 the movement of food-gathering cilia, tentacles, etc. The distinction 

 is primarily one of initiative, the herbivore, for example, being the 

 agent that acts upon the plant matrix or some portion of it. This 

 essential relation is maintained even by plant parasites upon animals, 

 in spite of striking disparity in size and motility. 



With further use of the term coaction, it may prove desirable to 

 distinguish between the two roles and to designate the initiating or 

 directing organism as the coactor and the receiving one as the coactee. 

 In the large majority of coactions, especially on land, animals take 

 the one part and plants the other, but the behavior is sometimes 

 reversed. 



In many social and symbiotic relations, the coactive organisms 

 may exhibit more or less parity in behavior, or at least in values 

 received. Such is the situation in a flock or herd where the members 

 are of the same species, and it obtains likewise in certain mixed herds 

 of mammals. Much more striking instances are to be found in the 

 symbiosis of microscopic algae with such animals as Stentor or Hydra, 

 or such plants as Cycas, of bacteria with legumes, and fungi with the 

 roots of orchids, as well as many trees. These are all mutually 

 beneficial, but the transition to pure parasitism is so gradual that no 



