32 Mamie Microbiology 



and fomiulae have been devised to convert chlorophyll units of 

 standing crop into dynamic units. However, the C^'* method is 

 more spectacular, and should, in theory, determine rate of assim- 

 ilation. Various techniques are employed, including incubation 

 for a period (usually 4-6 hours) in a light bath, incubation in 

 sunlight with a range of filters to simulate depth, and incuba- 

 tion in the sea at the depth from which the sample was taken, a 

 method which can involve the experimenter in unrehearsed aquat- 

 ic sports. From correlations with fluorescence counts of phyto- 

 plankton made recently over fourteen stations at depths from 

 surface to 150 m, it seems possible that the C^^ technique meas- 

 ures standing crop rather than the rate of production, or that, in 

 uniform water masses, standing crop may relate directly to rate 

 of production. 



Such measurements, moreover, take no account of the phys- 

 iological state of the organisms, or of reproductive rhythms. It 

 is not sufficient to know that a phytoplankton sample is assimilat- 

 ing at a given rate. One must know the rate of change of that 

 rate, as blooms in the sea are often of very short duration, and, 

 in mixed waters, may be limited in space. To my mind, the biolo- 

 gy of phytoplankton is the most important study at the present 

 time. 



Motoda and Kawamura (Chapter 26) consider from their 

 studies that phytoplankton adapts itself so that its maximum rate 

 of photosynthesis corresponds to the light intensity of the area; 

 in more northerly waters, the maximum rate will be at a lower 

 light intensity than in more tropical waters with a higher light 

 intensity. This is an interesting possibilitv. 



EXTERNAL METABOLITES IN THE SEA 

 AND SUCCESSION 



The study of external metabolites in the sea is rather popular 

 at the present time, since the suggestion by Lucas (3, 4) of their 

 importance and particularly the importance of exocrines. There 

 is no doubt that extracellular substances are produced by marine 

 organisms, but their importance as stimulative or repressive agents 

 in phytoplankton succession is yet quantitatively unknown. Smay- 

 da gives his reasons for doubting their importance, but a great 



