THE LABORATORY CULTIVATION OF STEMONITIS

ALEXOPOULOS, CONSTANTINE J. (State U. Iowa, Iowa City.) The laboratory cultivation of Stemonitis. Amer. Jour. Bot. 46(2): 140-142. Illus. 1959.-The cultivation of a species of Stemonitis, probably S. flavogenita, in laboratory culture is reported here for the first time. The organism completed its entire life cycle on artificial media from spore to spore, in the presence of contaminating bacteria, in 36 days. The plasmodium, characteristically different from those of the Physarales, is described and illustrated. IN SPITE of statements published from time to time which convey the impression that cultures of the Myxogastres are very difficult to obtain from spores, some 20 or more species have been previously cultivated in the laboratory and have completed their life cycles on artificial media. Physarum polycephalum, Didymium nigripes, Didy7nium squamulosuzm, Fuligo septica, Physarella oblonga, to mention only a few, are well known by students of the Myxogastres for the ease with which cultures may be obtained from spores. P. polycephalum has been used extensively for physiological studies by a large number of biologists. D. nigripes is perhaps second only to P. polycephalum as the object of extensive investigations, because of the ease with which plasmodia and fruiting bodies may be obtained on agar culture. It will be noted, however, that all of the above mentioned organisms belong to the order Physarales. It is certainly true that reports of culturing Myxogastres belonging to other orders are very rare indeed. Licea flexuosa has been grown in pure culture by Sobels (1950), but the initial material was obtained in nature as a sclerotium and no claim is made that plasmodia were obtained in culture from spores. The life history of Reticularia lycoperdon was worked out in a classic investigation by Wilson and Cadman (1928), but only a portion of the life cycle was observed in culture, some of the stages having been collected in nature and brought into the laboratory for study. The same is true for Ceratiomyxa fruticulosa (Gilbert, 1935), one of the Exosporeae, and of many other Myxomycetes not members of the Physarales. As a matter of fact, with the notable exception of Hemitrichia vesparium, cultured on corn decoction agar by Gray (1938), there are few other convincing published reports of successful culture of Myxogastres other than Physarales on artificial media from spore to spore. Constantineanu (1906) reported the completion of the life cycle of Perichaena depressa on tanbark, and Gray (1938) obtained sporangia of Lamproderma arcyrione7na by 'Received for publication August 25, 1958. I am indebted to the Graduate College of the State University of Iowa for providing me with the services of a research assistant, Mr. O'Neil Ray Collins, who helped me with this work. sowing spores on moist, decaying (sterilized ?) wood. Constantineanu (1906) includes Stemonitis fusca in a list of Myxomycetes which yielded plasmodia from spores on solid media, but makes no further reference to this organism even though he devotes at least one subsequent paragraph to each of the others on that list. Gray (1938), referring to Stemonitis axijera and S. fusca with which he was working, stated ". . . there are no records of either species having been artificially cultured, and to date no methods for their cultivation have been devised." The spores of a number of species of the Stemonitales have been germinated, and syngamy has been observed more than once. Plasmodium formation in this group was reported most recently by Ross (1957), but, to my knowledge, none of the Stemonitales has been induced to complete its entire life cycle on artificial media, except for the Lamproderma mentioned above. It was of great interest to me in April 1958, therefore, to observe a yellowish plasmodium which appeared in a Petri dish culture of Physarella oblonga on corn meal agar, collect in a mass on the underside of the Petri dish cover and produce a number of sporangia typical of the genus Stemonitis. The sporangia were attached on a common hypothallus, and they as well as the spores, were perfectly formed. Inasmuch as the Physarella culture had been initiated through the sowing of spores, it was obvious that spores of a Stemonitis had been accidentally introduced into the Petri dish and the organism had completed its life cycle from spore to spore on artificial media. Soon after the spores had matured, a single sporangium was detached from the hypothallus with sterile forceps and rubbed on the surface of half-strength Difco corn meal agar in a Petri dish to distribute the spores. Two ml. of sterile distilled water were poured on the spores and the dish was incubated at 200C. Plasmodia appeared in 6 days and were kept in culture by transferring to new Petri dishes on a variety of media. No difficulty was experienced in ridding the cultures of contaminating fungi, but no attempt was made to purify the plasmodia from bacteria which were present in large numbers in all the cultures. One small plasmodium was transferred on May 19 to a