. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ON THE RELATION BETWEEN GROWTH AND MORPHOGENESIS IN THE SLIME MOLD DICTYOSTELIUM DISCOIDEUM 1 MAURICE SUSSMAN Dcpi. of Biological Sciences, Northivcstern University, Evanston, Illinois In the normal course of cellular slime mold development, the myxamoebae pass through the exponential growth phase and, upon its cessation, aggregate in multi- cellular masses. The number of aggregative centers formed has been shown to be a function of the number of cells and of the population density (Sussman and Noel, 1952). From these and ot

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. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ON THE RELATION BETWEEN GROWTH AND MORPHOGENESIS IN THE SLIME MOLD DICTYOSTELIUM DISCOIDEUM 1 MAURICE SUSSMAN Dcpi. of Biological Sciences, Northivcstern University, Evanston, Illinois In the normal course of cellular slime mold development, the myxamoebae pass through the exponential growth phase and, upon its cessation, aggregate in multi- cellular masses. The number of aggregative centers formed has been shown to be a function of the number of cells and of the population density (Sussman and Noel, 1952). From these and other relationships (Sussman, 1952) it can be inferred that each aggregate requires for its formation the presence of a special cell called an initiator, to which neighboring cells respond, and only a small proportion of the population can so serve under the conditions employed. In Dictyostclium discoideum wild type, the ratio of the initiator to responder cells has been found to be 1:2200. That the system is under genetic control is shown by the fact that mu- tants of D. discoideum, as well as wild type representatives of other species, display significantly different ratios (Sussman and Noel, 1952; Sussman, 1955). In the past, Raper (1940) has presented evidence to indicate that aggregation can begin only when growth ceases and that the aggregation of a stationary phase population can be prevented and indeed reversed by further additions of nutrient material. The present study demonstrates an extension of this conclusion: that is, that cells taken from any phase of the growth cycle, including newly germinated spores, can aggregate when further growth is prevented and, in fact, give quantita- tively the same aggregative performance as do stationary phase myxamoebae. METHODS A. Organisms and media. The organism used in this study is representative of D. discoideum Raper, strain NC-4. Stock cultures were grown on glucose- peptone agar in association with A. aerogenes by methods pr