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The rust fungi have long been regarded as strict obligate parasites of vascular plants, and as far as the authors can determine, with the exception of an unsubstantiated note by Ray3 in 1901, no authentic report has appeared of the continued growth in culture of these fungi in the absence of their specific host plant. Since precise studies on the nutrition and metabolism of these organisms can hardly be carried out in the presence of host plant tissue an attempt was made to adapt these obligate parasites to a saprophytic mode of existence. It appeared feasible to culture rust infected tissue of a susceptible host by the classic methods of White4 and Gautheret,' and then by varying the cultural conditions to which these relatively undifferentiated host tissues were exposed, to condition the parasitic mycelium of the rust to a less specialized environment, and ultimately perhaps to render it independent of its host. Morel2 previously attempted to culture several rusts on undifferentiated tissues, but attributed his lack of success to inadequate inoculation techniques.The rust selected was Gymnosporangium juniperi-virginisanae Schw. which forms characteristic cornute aecia or roestelia upon Crataegus and Malus and telial galls upon its alternate host Juniperus virginiana. In eastern North America the roestelia are produced in early summer and aeciospores from them infect the leaf axils of cedar. The telial galls begin to develop the following April, and grow throughout the summer and fall. These galls produce gelatinous telial horns in the succeeding spring. Germination of the teliospores in these horns results in the production of numerous basidiospores which reinfect the rosaceous host. The mycelium of the rust is thus systemic in the cedar galls during the winter months, and this stage was selected as the starting point for this investigation.Telial galls collected at intervals during the fall and winter in Branford Township, Conn., were soaked for two minutes in 95 per cent ethyl alcohol, the outer cortex removed under aseptic conditions and the inner parenchyma containing the rust mycelium sectioned into small cubes which were dipped into 0.1 per cent sterile ascorbic acid and then placed upon nutrient agar in sealed test tubes. This technique has been described by Gautheret' and his nutrient solution No. 4 was employed as the basic culture medium throughout the experiments. The following modifications promoted more rapid growth of the gall calluses: the dextrose concentration was raised to 3 per cent and 500 ppm. of ascorbic acid was added to the 400 PROC. N. A. S.

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