A strain of (designated . ) which produces fragile cysts was isolated from soil. Fragility of the cysts was measured by ultrasonic treatment and compared to the fragility of cysts of a typical strain of . . Differences in fragility and resistance to ultraviolet radiation were observed but differences in desiccation resistance were not perceptible between the two strains. Electron micrographs of cysts of the new isolate revealed a structural aberration in the exine area of the cyst coat which may be associated with the physiological differences described. The morphological aberration and the fragility of the cysts are inheritable traits of this strain of . .


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