AQUATIC ORGANISMS AND EXTERNAL METABOLITES 503 



substances, (b) "growth" substances, and (c) "behavior- 

 stimulating" substances.* 



However this may prove to be, the witches' brew which the 

 seas comprise, and the evidence we are slowly obtaining provides 

 the necessary basis for mediating some of those features of marine 

 ecology which had previously been puzzling: some aspects of the 

 initiation of the spring outburst, of the flowerings which occur at 

 water boundaries and above all of "succession" itself. Here, too, 

 we can be sure lies at least a part of the explanation of the facts 

 which led Hardy (1935) to postulate his theory of animal exclusion. 

 The metabolism, and ultimately death, of one organism is always 

 modifying the environment of another. If that modification is 

 appreciable, the others must either be tolerant or must adapt 

 themselves in order to succeed. Some organisms appear to be 

 susceptible and must have an avoiding reaction or fail; others 

 appear to have evolved a significant deficiency which certain 

 neighbors can supply — doubtless attaining increased efficiency 

 elsewhere in their own metabolism at the cost of an increased 

 dependence! Some benefit without that necessity; others may be 

 merely tolerant, although over the generations mere tolerance is 

 unlikely. In one way or another, these "dependencies" give at 

 least an appearance of integration in the community. It is not the 

 close integration which characterizes the organized body, nor is it 

 just the product of the inorganic environment. It is a loose but 

 organic integration. In some respects its extreme developments 

 may be found in true symbiosis and parasitism. Given the facts, 

 evolution could be expected to bring about such relationships, 

 including reciprocal relationships, some of which would indeed be 

 "group symbioses on the large scale." 



Since 1938, and particularly since 1947, several of these possi- 

 bilities have been confirmed as facts, chiefly by experiment.! 



* A very interesting discussion of interrelationships and terminology in this and 

 bordering fields is given by Karlson and Liischer (1959). 



t While only representative, reference may be made to the various papers listed 

 by Lucas, (1938, 1947, 1949, 1955, and 1958), references here will mainly be selected 

 from papers published recently; relevant bibliographies are given by Provasoli 

 (1958), Hutner et al. (1958), and Saunders (1957), as well as in papers contributed 

 to the afternoon sessions of this Congress. 



