Trevithick, John R. (University of Wisconsin Medical School, Madison), Robert L. Metzenberg and Donald F. Costello. Genetic alteration of pore size and other properties of the Neurospora cell wall. J. Bacteriol. 92:1016-1020. 1966.-Several properties of the cell walls of wild type and the osmotic mutant of Neurospora crassa have been examined. The peameability of the isolated cell walls to polyethylene glycol and dextran polymers of different molecular weights was investigated by the volume of distribution technique. The exclusion thresholds were evaluated by a statistical treatment. The molecular weights corresponding to these thresholds for wild type and osmotic were approximately 4,750 and 18,500, respectively; these values are significantly different. The cell walls of osmotic appeared to be thinner, more easily broken, and more easily compressed to ribbonlike shapes, whereas those of wild type were tubular and strong. Chemical analysis showed that osmotic walls had roughly a 30-fold higher galactosamine-glucosamine ratio than did wild type. It is proposed that the osmotic mutant has a cell wall with abnormally large pores, and that this may account for the increased rate of egress of invertase and the decreased fractionation of light from heavy invertase in this strain.