502 CYCLES OF ORGANIC AND IXORGAXIC SUBSTANCES 



(thiamin, niacin, steroids, organic acids, etc.) are known and 

 Others are being found (e.g., Provasoli, 1958; Vishniac, 1955; also 

 \-arious contributors to the afternoon sessions of this Congress). 

 A recent development is the demonstration by Dr. Bentley, at 

 Aberdeen, that potent substances resembling the growth hormones 

 of higher plants are produced by planktonic and other algae and 

 even by zooplankton, and are released into the medium (Bentley, 

 1958; 1959). There are results, too, which demonstrate that some 

 free metabolites may be harm.ful to other members of the com- 

 munity while, as was foreseen, there are hints that sometimes the 

 same metabolite may be harmful to some and necessary, or at least 

 beneficial, to others. This may be one aspect of the evidence that 

 there has been adaptation to optimum concentrations of the 

 metabolite in question. Meanwhile, in his paper. Professor 

 Friedrich (p. 257) gave us food for thought in his reference to the 

 photosensitizing possibilities of many of the fluorescent substances 

 present in the sea. 



Just a moment's thought about the wide range of substances 

 (from carbon dioxide to B12) with which we can be concerned 

 (e.g., \'allentyne, 1957) suggests the need for some classification. 

 In my enthusiasm for the general thesis, I was all too negligent 

 about this previously, and proper attention cannot be given to it 

 here. Meanwhile, I will roughly distinguish, for future analysis, 

 (a) substances such as the grosser products of decay and excretion 

 (amino acids, carbohydrates, etc.), perhaps together forming the 

 bulk of organic compounds in the sea; (b) those more diffuse 

 substances such as carbon dioxide and oxygen which are still very 

 appreciable and, moreover, are metabolites exerting immediate 

 and vital effects on other organisms in the community; and (c) 

 those which, broadly speaking, are measurable in terms of parts 

 per million or even less. The last in turn, for the present, may be 

 divided into (a) known and potent metabolites within the body, 

 such as B12, which may be expected (and in some cases shown) to 

 play similar parts within the community — perhaps the term 

 ectocrines is best restricted to these — and (b) less known substances 

 with which members of the community may have developed eco- 

 logical links or sensitivities. Alternatively, there is the possibility 

 of a functional classification, loosely divisible. into (a) "nutrient" 



