The Ascocarpic Stage of Species of Scopulariopsis

Abstract

The writers have studied in culture an ascomycete having a Scopulariopsis conidial stage and an ascocarp stage which corresponds to Microascus, except perhaps that it has triangular ascospores, whereas Microascus sordidus has kidney-shaped spores. This new species is described as Microascus trigonosporus, and its conidial stage is referred to as Scopulariopsis trigonospora. The ascocarp arises from a coiled ascogonium which becomes enveloped in a hyphal weft of several layers of cells. Later this envelope becomes differentiated into an outer wall of dark-colored carbonized cells and an inner portion consisting of thin-walled colorless cells. The cells immediately surrounding the ascogonium begin to elongate inwardly, crowding in to fill up the space made available because of intercalary growth of the outer wall. A papillate ostiolar portion is then organized and its cavity formed schizogenetically. Because the outer wall increases in its circumference more rapidly below and at the sides than at the top, and because the inward growing hyphae develop more rapidly from below than from above, the ascogonium becomes placed well above the center and just beneath the ostiole. Most of the growth of the thin-walled cells is upward and inward. The ascogenous hyphae sometimes grow out from the ascogonium in all directions, but usually most of the growth, because of the position of the ascogonium, is outward and downward, and, therefore, back against the upward inward growing rows of sterile cells. These sterile cells are gradually absorbed and their place in the cavity is taken by ascospores set free as the asci deliquesce. The ascospores are discharged in long slender cirrhi containing a cementing substance which hardens on drying and which then is dissolved in water only very slowly. Microascus intermedius develops only ascocarps which in their organization, in general, correspond very well with Microascus of Zukal and, except for the absence of a conidial stage, it resembles Sopp's Acaulium albo-nigrescens. These two species, because of the Scopulariopsis conidial stage of one, and because of their black carbonaceous ascocarps with ostioles, and the growth of the ascogenous hyphae outward from the ascogonium in all directions, seem to make the series including Penicillium, Aspergillus, Thielavia, Scopulariopsis, Microascus, Acaulium, Peristomium, Nephrospora and Chaetomium, more complete.