A new method for assaying vitamin B 12 in seawater using the marine diatom Cyclotella nana Hustedt is described. The criterion of response to variations in B 12 concentration was C 14 assimilation (added as Na 2 C 14 O 3 ) after 24‐hr exposure to the vitamin. C 14 assimilation was proportional to the B 12 content of the medium in an ecologically useful range (0.1–6 µµ g B 12 /ml) .
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Kenneth Gold (1964) studied this question.