Conidiomatal morphogenesis and pleomorphic conidiogenesis in Scleroconidioma sphagnicola

Morphogenesis of microsclerotia and conidiomata, and conidiogenesis in Scle roconidioma sphagnicola were studied primarily by transmission and scanning electron microscopy. Microsclerotia were initiated as bulges from hyphae t hat later swelled and became multicellular. They increased in size by formi ng protrusions that subsequently were delimited by multilayered, simple sep ta. The structure of septa indicated an ascomycetous affinity. Cells of mat ure microsclerotia contained large lipid bodies and poorly defined organell es. In culture, microsclerotia often became conidiomata by conversion of th e surface cell layer to conidiogenous cells. These conidiogenous cells were either percurrently proliferating or were phialides with a collarette and periclinal wall thickening. Conidia were also produced from vegetative hyph ae. Conidiogenous cells arising from juvenile, hyaline hyphae proliferated percurrently or occasionally sympodially with the production of successive conidia. As the colony aged and hyphae became darkly pigmented, variously s haped, solitary hologenous conidia became more dominant. Secondary conidiat ion from these conidia was frequent. Relative juvenility of the cell wall a t the conidiogenous locus and the age of the colony appear to be important factors in determining the mode of conidium development in S. sphagnicola.