An Undescribed Lagenidium Parasitic Upon Potamogeton

Abstract

Phycomycetous parasites in the root hairs of terrestrial plants have been reported in numerous instances, but the presence of these organisms in the root hairs of aquatic plants has been largely overlooked. This paucity of records may be due to the fact that, until recently, the presence of root hairs on the great majority of aquatic plants had not been realized. Consequently, it is of interest to record the occurrence of a Phycomycete parasite infecting the root hairs of a true aquatic and causing a marked hypertrophy of these structures. In May 1941, Dr. W. C. Muenscher of this University called the writer's attention to a collection of seedlings of Potamogeton spirillus Tuckerman with root hairs showing curious pyriform or spherical swellings. Many of these swollen hairs were hyaline and completely empty, but spore-like bodies which resembled Pythium oogonia were present in a few. There was, however, no trace of any mycelium in either the root hairs or the cells of the root. Further search revealed root hairs in which the protoplasmic contents had apparently been incorporated into an amoeboid mass lying in the swollen tip of the hair. These lobulated masses were immediately suggestive of the thalli of the Lagenidiaceae. During the course of the preliminary study, one of these amoeboid thalli produced a number of zoospores; but it was not possible at the time to ascertain definitely the flagellation of these swarmers. A second collection of more mature seedlings taken from the same locality on July 2, 1941, showed an occasional infected root hair; but in this instance, only the amoeboid thalli were present, and zo6spore discharge was not observed. Obviously the affinities of this organism could only be determined by a careful study of its zo6spores. With this in mind, another collection was made from