|Title||Observations on chytridiaceous parasites of phanerogams. XXVIII. Physodermas on Sium suave|
|Publication Type||Journal Article|
|Year of Publication||1979|
Two Physodermas have been found on the umbellifer Sium suave. Physoderma Type I on submerged parts forms large conspicuous black pustules on stem and petiole and target spots on the leaflet lamina and on flowers. The other develops inconspicuous scattered reddish-black unraised flecks composed of tight aggregations of resting spores on petioles and lamina of underwater leaves. No reinfection of Sium suave could be induced by R. S. zoospores of Type I save for a few abortive epibiotic structures. On the grass Agropyron repens epibiotic, unilateral sporangia of Type I were formed readily as was the endobiotic stage after exposure to Type I R. S. zoospores, and the endobiotic stage with resting spores. The latter were also produced on Elymus canadensis seedlings and mature leaves of the rosaceous Potentilla anserina. Type II R. S. zoospores formed abundant resting spores and epibiotic sporangia of the bilateral type on seedlings of Sium suave.