Abstract
THE discovery this autumn of black scab in the potalo crop in two localities in co. Down was the means, through the Irish Department of Agriculture, of supplying me with excellent material of diseased tubers for examination. I have kept the resting “spores” of the chytridian fungus Chrysophlyctis endobiotica, Schilb., causing the disease, under varied conditions of temperature, nourishment, moisture, and light, and have succeeded in causing the “spores” to germinate, especially by cultivation in potato juice. Each “spore” proves to be a zoosporangium, full of zoospores or zoogonidia, seen in active swarming motion before rupture of the sporangium. The zoospores, 1.5–2 in diameter, escape through a slit-like opening in the wall of the sporangium 30–60 μ in diameter, and have the usual characters of a chytridian zoospore.
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