ULTRASTRUCTURE OF THE ASCUS APICAL APPARATUS IN SPECIES OF CENANGIUM,ENCOELIA, CLAUSSENOMYCES AND ASCOCORYNE

The ascus apical apparatus and dehiscence mechanism were studied with TEM in Cenangium ferruginosum and Encoelia fimbriata, and Claussenomyc es atrovirens and Ascocoryne cylichnium. The asci, which are non-react ive with iodine in all species except the last mentioned, varied in ge neral morphology of the apical apparatus and dehiscence mechanism. The apical apparatus in C. ferruginosum was extremely small, with an annu lus fully occupying the apical thickening. It played no particular rol e in dehiscence, but the tractus and apical funnel demonstrated in thi s species were associated with it. The ascus opened by an irregular sl it. The apical apparatus in E. fimbriata was characterized by a well-d eveloped apical thickening, which lacked an annulus, surrounding a bro ad, cylindrical structure. This structure became externally eroded and stretched during maturation of the ascus, and was finally tom in an a lmost circular fashion apparently functioning as a lid. It is argued t hat this structure is probably homologous to the central cylinder in o ther Leotiales which form an annulus in their apical thickening. The s imilarity to the operculum characteristic of the Pezizales seems to be merely a case of convergence in structure and function. The apical ap paratus was different from several other species of Encoelia, includin g the type species. The ascus in CI. atrovirens is similar in general morphology and reactivity pattern of the annulus to that in Leotia lub rica. The ascus in A. cyclichnium lacked an annular protrusion, and re sembled more closely that in Hymenoscyphoideae than Sclerotiniaceae.