Abstract
Mode of growth of Leucothrix mucor filaments was measured by autoradiography with tritiated thymidine. Studies were performed on L. mucor in pure cultures in free suspension, as an epiphyte of pure cultures of the red alga Antithamnion sarniense, and as an epiphyte of red algae in the sea. Statistical analyses of the distribution of growing cells was done by use of the nonparametric One-Sample Runs Test and a Cluster analysis adapted from quadrat analyses of plant ecologists. No evidence of preferential growth at base or tip of L. mucor filaments was obtained in any of these studies. However, in nature, but not in the laboratory, there were regions of L. mucor filaments which were nongrowing or dormant. Such nongrowing regions could incorporate tritiated glucose.