Illustrations, tables, literature cited p. 404

Averting pairs of cultures of D. maydis when seeded simultaneously in potato-dextrose broth and incubated for 10 to 20 days at a temperature ranging between 22⚬ to 25⚬C, produced filtrates that were toxic to cultures of the same species and to a number of other fungi. Toxicity of filtrates appeared not to be due to H-ion concentration. Toxic filtrates were produced only in stationary culture. Filtrates from shake cultures, or from those in which the medium was agitated with a stream of sterile air or by a mechanical stirrer, were non-toxic. Filtrates produced by single cultures were not toxic. When two such filtrates were combined in equal volume the resulting mixture was non-toxic, even though the cultures produced a toxin when incubated together. Comparable filtrates produced by paired compatible cultures were not toxic. 2. The maximum dry weight of mycelial mats produced by paired averting cultures was attained about 8 days after seeding the broth and then remained constant for the remainder of the incubation period (18 days). The dry weight of mycelial mats harvested from paired compatible cultures increased steadily over the incubation period and, at the termination of the experiment, exceeded by five times the dry weight of mats of the paired averting cultures. 3. Chloroform was effective in extracting the toxic material from filtrates of paired averting cultures, but ethyl ether, ethyl acetate and petroleum ether were not effective.

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