APHANOMYCES PHYCOPHILUS IN CULTURE

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APHANOMYCES PHYCOPHILUS De Bary, one of the rarer Saprolegniales, was first described by DeBary in 1860 from a collection made at Frankfort am Main. Since then it has been reported from Michigan by Kauffman (1915), from Indiana by Weatherwax (1914), from New York by Sparrow (1933), and from North Carolina by Couch (1926). Previous attempts to obtain saprophytic growth of this parasite have been unsuccessful. DeBary says that it is parasitic on Spirogyra and Zygnema and is not to be cultured on decaying Phanerogam remains and dead animals. The purpose of this paper is to describe experiments in which it has been possible to induce growth of Aphanomyces phycophilus on artificial culture media. GROWTH ON SPIROGYRA.-The hyphae, 8-15 ,. thick, grow lengthwise through the Spirogyra filament by penetration of the cross walls. The tip of the growing hypha upon coming in contact with the cross wall of the host becomes somewhat flattened and presses against it as the wall becomes thinner. When a hole has been dissolved in the wall, the hypha pushes through it rapidly into the adjoining cell, which becomes plasmolysed. One hypha was seen to grow through one cell, a distance of 150 , in 20 minutes. After traversing the length of the cell along the surface of the plasmolysed protoplast, the hypha sends down lateral branches among the chloroplasts. The main hypha may continue on into the next cell, or a lateral branch may penetrate the side wall and grow out some distance into the water and parasitize another Spirogyra filament. Oogonia, 40-50 , in diameter, are formed on the ends of short lateral branches and seem to be intramatrical as often as extramatrical: The oogonial wall is drawn out into a number of spines, 7-9 # in length, and is yellowbrown in color. The single brownish oospore, 24-31 , in diameter, is finely granular, with one or two rows of oil globules around the periphery. The curvedclavate antheridia develop on the ends of nearby lateral branches and often wind around the hyphae bearing oogonia. There are one to three antheridia on each oogonium. No spores were observed. ISOLATION AND CULTURE ON AGAR.-A fungus was found growing parasitically on Spirogyra in a collection made by Mrs. H. B. Gotass on April 16, 1938, from a small stream near Chapel Hill. The size of the hyphae, the mode of growth, the structure of the oogonia, and the antheridia all agreed with DeBary's description and figures of Aphanomyces phycophilus. It differed from Wille's (1899) description of A. nor-