On July 1, 1948, 100 millicuries of radioactive phosphorus, P32, was added to the surface of an acid bog lake of area 0.3 hectares (0.8 ac.) and depth 6 m., situated near Halifax, Nova Scotia. The lake had a well developed⁁ zone of cold, stagnant water at the bottom with a thermocline above. Within a few hours the P32 was taken up strongly by the sphagnum (which made up most of the lake margin), by the floating plankton, and by sponges. Within a few days it had reached the bodies of fishes (Fundulus and Notemigonus), and within a fortnight had accumulated in their skeletons and viscera. No appreciable uptake of P32 by such bottom rooted forms as the cranberry (Vaccinium) and leather leaf (Chamaedaphne) was observed for more than two weeks. Penetration of added phosphorus into the lake depths was very slow, and even at the end of eight weeks the material was only doubtfully detected at the bottom. There was no evidence of active uptake by bottom mud. The ratios of maximum count per wet weight of organism to maximum count for the same quantity of lake water were as follows:Zooplankton 40,000Fundulus 13,000Sponge 4500Sphagnum 400Vaccinium 300Blue-green alga 300Chamaedaphne 100Nuphar 80