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Lotic species of freshwater algae have a higher respiratory rate in a current as compared with that in still water. Species in 4 classes (Chlorophyceae, Xanthophyceae, Bacillariophyceae, Rhodophyceae) were tested. A correspondingly higher uptake of P[SUP32] was also noted. The fact that the increase in metabolic rate results from the sweeping effect of a current was indicated by the lower mineral uptake of filaments floating free in a current as compared with that of filaments held still in the current in the same container. The current effect was evident even at current speeds as low, as 1-4 cm/sec. [ABSTRACT FROM AUTHOR]