mutant strains of Polysphondylium pallidum. microcyst differentiation in wild-type and Calcofluor staining of cellulose during

in 15-g MSMhave been described in detail (A. H. C. Choiand D. H. O'Day, submitted for publication) and are onlysummarizedbriefly here to clarify the morphological eventsofencystment. Encystment ofWS-320began at day 3. Byday 4, about 86%ofthe culture had already encysted, andca. 95%microcystswereobservedbyday7(Fig. 1A). Strainmic-1 began to encyst between day 2 and 3. Eventually,about 30%microcysts were formed (Fig. 1B). Strain mic-2started to encyst at aboutthe sametime as WS-320. Byday7, about 77% microcysts were observed. Under phase-contrast microscopy, some of the microcysts that formedappeared abnormal (Fig. 1C). The abnormal microcystsappeared to be surrounded by cell walls but they did nothave the normal dense cytoplasm characterizing normalmicrocysts, andsomeofthempossessedagapbetweentheirwall and the cell. At day 7, over 20%abnormal microcystsexisted in the mic-2 cultures.Stainingofencysting cultures with Calcofluor. Theappear-