AbstractThe horizontal distribution of Ceratium hirundinella (MÜLL.) BERGH was investigated in Lake Erken at ten stations in the summer of 1969. Abundance, total length and number of horns were studied. The conclusion is that the lake contained a horizontally uniform population of the alga. A correlation between form variation and the growth curve of the population was found, which can be explainable with PEARSALL'S (1929) theory, linking form variation with cellular metabolism