Alterations of plaque morphology in some coliphages.

occurred on the plates, isolations were made from those areas to slants. None of the isolates formed aerial hyphae on glucose-asparagine agar. The interactions of the paired strains are given in table 1. For clarity, only reactions concerning the stimulation of aerial hyphae are reported. It is apparent that some strains could stimulate others, although unable themselves to form aerial hyphae; however, there were no mutual stimulations. In some cases (B, G, H, and J), the positive reactions were quite limited and atypical, the hyphae being abortive and suggestive of mesophilic micromonosporas rather than of streptomycetes. S. griseus, which normally formed aerial mycelium abundantly, could be stimulated beyond its normal capacity on this medium. The reversion of the stimulated isolates to their defective condition indicated that the production of aerial hyphae was not the result of a genetically induced change.