Some Fungus Parasites of Algae
About twelve years ago I was giving considerable attention to the study of the parasites of the algae in the vicinity of Ithaca, N. Y. At that time I hoped that the investigations might eventuate in a monograph of the Chytridiales of the Cayuga Lake basin. The pressure of other investigations has almost completely interrupted these studies. Because of our limited knowledge of the occurrence and habits of these interesting fungi in North America, it has seemed to me desirable that the
... that the observations already made should be recorded, in the hope that this may stimulate a greater interest in these plants. As a result of the studies three papers have already been published. An extended paper on the genus Harpochytrium in the United States was published in I903,2 a summary of which later appeared in the Journal of mnycology in I904.3 A short note on the interesting behavior of the zoospores of Rhizophidium globosum while escaping from the zoosporangium was published in I894.4 This behavior related to the habit of their sensing or feeling the exit opening in the sporangium, which they do by means of pseudopod-like extensions of the protoplasm in different directions, after having come to rest on the inside of the zoosporangial wall. In case they happen to come to rest close by the exit they "feel" it by one of the pseudopods, and slide out. In case they are distant from the exit, not finding it they round up into the motile zoospore form again and swarm around in the zoosporangium for a time, and coming to rest make another trial. It is evident that when the zoosporangium is filled with the zoospores the latter will escape quite rapidly A; < X X for a time because so many of XD them are crowded successively against the exit. As the num-B Lers diminish there is greater freedom for swarming. The zoospores then swarm around and around in great circles FIG. i. Rhizophidium globos.tmn (A-Br.) inside the wall of the zoospo-Schrot. A young plant, shortly aft r rangium, now and then coming germination of zoospores with germ tubes, penetration tube forming rhizoicis; B u mature plant ready to form zoospores; exit. This same behavior has C zoospores escaping; D much smaller been observed in the case of a plants. number of other species. In addition to this a quite remarkable phenomenon was observed in the case of another species, Rhizophidium brevipes, which will be described below. In the presentation of these observations I shall make no attempt to arrange the genera in any natural order of relationship, this matter being reserved for a future work. Since a number of species of Rhizophidium were studied I will begin with this genus. RHIZOPHIDIUM BREVIPES This was collected in a pool beyond Forest Home, N. Y., a little more than one mile from Ithaca. It was attached to the wall of a fruiting cell of Spirogyra varians. The zoosporangium is oval with a small apical papilla. The wall shows two distinct layers, an outer rather thick one and an inner thin one. At the time of the maturity of the zoospores the papilla of the outer layer becomes gelatinized at the apex, forming a minute opening about 4,0 in diameter. One very characteristic feature of this species is the very rudimentary condition of the rhizoids. The very slender branched rhizoids so characteristic of R. globosum and other species appear to This content downloaded from 129.