president's address. 25 



must be rejected, or at least greatly modified. His estimates of the 

 plankton were minimum ones, while it seems probable that his figures 

 for the organic carbon present represent a variable amount of organic 

 matter arising from one of the reagents used in the analysis.-* The 

 later experimental work of Henze, of Eaben, and of Moore shows that 

 the organic carbon dissolved in sea-water is an exceedingly minute 

 quantity, well within the limits of experimental error. Moore puts it, 

 at the most, at one-millionth part, or 1 mgm. in a litre. At the Dundee 

 meeting of the Association in 1912 a discussion on this subject took 

 place, at which Piitter still adhered to a modified form of his hypothesis 

 of the inadequacy of the plankton and the nutrition of lower marine 

 animals by the direct absorption of dissolved organic matter. Further 

 work at Port Erin since has shown that, while the plankton supply 

 as found generally distributed would prove sufficient for the nutrition 

 of such sedentary animals as Sponges and Ascidians, which require tc 

 filter only about fifteen times their own volume of water per hour, 

 it is quite inadequate for active animals such as Crustaceans and Fishes. 

 These latter are, however, able to seek out and capture their food, and 

 are not dependent on what they may filter or absorb from the sear 

 water. This result accords well with recorded observations on the 

 irregularity in the distribution of the plankton, and with the variations 

 in the occurrence of the migratory fishes which may be regarded as 

 following and feeding upon the swarms of planktonic organisms. 



This then, like most of the subjects I am dealing with, is still a 

 matter of controversy, still not completely imderstood. Our need, then, 

 is Research, more Research, and still more Research. 



Our knowledge of the relations between plankton productivity and 

 variation and the physico-chemical environment is still in its infancy, 

 but gives promise of great results in the hands of the bio-chemist and 

 the physical chemist. 



Recent papers by Sorensen, Palitzsch, Witting, Moore, and others 

 ha\ie made clear that the amount of hydrogen-ion concentration as 

 indicated by the relative degree of alkalinity and acidity in the sea- 

 water may undergo local and periodic variations and that these have 

 an effect upon the living organisms in the water and can be correlated 

 with their presence and abundance. To take an example from our 

 own seas. Professor Benjamin Moore and his assistants in their work 

 at the Port Erin Biological Station in successive years from 1912 

 onwards have shown"' that the sea around the Isle of Man is a good 

 deal more alkaline in spring (say April) than it is in summer (say 



^* See Moore, etc., Bio.-Chem. Journ. vi. p. 266, 1912. 



"^ ' Photosynthetic phenomena in sea-water,' Trans. Liverpool Biol. Soc. 

 xxix. 233, 1915. 



