Fungi, Ascomycetes, Ustilaginales, Uredinales . hemost part on seed plants but in some cases on Pteridophyta, Bryophyta orLichens. The perithecia are immersed in the substratum, the ostiole onlyprojecting, but they may become more or less exposed by the rupture of thecovering tissues. The peridium is leathery or membranous. The genus Pleospora includes some 225 species, several of which occuron grains and other grasses where they show biological kerbarum is a facultative parasite on the leaves of angiosperms ;the perithecium is initiated by the division of a hypha into
Fungi, Ascomycetes, Ustilaginales, Uredinales . hemost part on seed plants but in some cases on Pteridophyta, Bryophyta orLichens. The perithecia are immersed in the substratum, the ostiole onlyprojecting, but they may become more or less exposed by the rupture of thecovering tissues. The peridium is leathery or membranous. The genus Pleospora includes some 225 species, several of which occuron grains and other grasses where they show biological kerbarum is a facultative parasite on the leaves of angiosperms ;the perithecium is initiated by the division of a hypha into numerous shortnils from which branches grow out. The central cells, and later the basalparts of the branches, divide in various directions till an irregular paren-chymatous mass is formed. By further growth and division the massassumes a globular shape and the central cells become elongated and differ-entiated as paraphyses. Later, asci appear, developing from the same cellsas the paraphyses and each produces eight muriform spores (fig. 120).. Fig. 120. Pleospora sp.; germinating spores, x 1000. M ulticellular conidia also develop on branched hyphae, the terminal cellsof which form the sterigmata. After the spore is shed the hypha may continueto grow, a new sterigma being formed above the old one. The name Macrospo-riumparasiticum was formerly applied to the conidial stage of this species. The genus Venturia includes over fifty species, several of which are para-sitic on living leaves; the perithecium is immersed and the large ostiole besetwith stiff hairs or bristles. The species grouped under Fusicladium amongthe I lyphomycetes are in some cases conidial forms of this genus. Theconidia are two-celled, borne on short conidiophores arranged in groups;/-. dendriticum is the cause of scab or black-spot on apples, and /?. Pyrinumof a similar disease on pears. 11 l62 PYRENOMYCETES [CH. Leptospliaeria includes some 500 species characterized by the papillateor conical ostiole, usual
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectfungi, bookyear1922
