. The fungi which cause plant disease . Plant diseases; Fungi. 208 THE FUNGI WHICH CAUSE PLANT DISEASE P. ruba (Pers.) D. C. causes reddish spots on the leaves of Prunus. Stroma at first bearing pycnidia (Libertella rubra) with filiform hooked, con- tinuous conidia. Perithecia produced on old leaves, bearing ellipsoid to elongate asci; spores 10-13 x 6 m, smooth. The invaded leaf'tissue is colored by the mycelium which bears a reddish oil. Nu- merous perithecia are immersed in the diseased area and, opening to the surface, extrude spores which seem incapable of in- fecting. During winter the s
. The fungi which cause plant disease . Plant diseases; Fungi. 208 THE FUNGI WHICH CAUSE PLANT DISEASE P. ruba (Pers.) D. C. causes reddish spots on the leaves of Prunus. Stroma at first bearing pycnidia (Libertella rubra) with filiform hooked, con- tinuous conidia. Perithecia produced on old leaves, bearing ellipsoid to elongate asci; spores 10-13 x 6 m, smooth. The invaded leaf'tissue is colored by the mycelium which bears a reddish oil. Nu- merous perithecia are immersed in the diseased area and, opening to the surface, extrude spores which seem incapable of in- fecting. During winter the stroma darkens, " turns hard and produces the perithecia and ^D, asd; E, TOnMk.' ascosporcs. Ascogouium and trichogyne-like After Fisch. ^^^^^ ^^^^ ^^^^ ;^ p. ochraceum (Wahl.) Sacc. occurs on Prunus padus. # Valsonectria Spegazzini (p. 198) Stroma thin, cushion-shaped, under the bark of the host; peri- thecia similar to those of Valsa, sunken in the stroma, the beak erumpent, red; asci cylindric, 8- spored; spores 2-celled, hyaline or light brown. A genus of but three species which differ from Valsa chiefly in their % red color. ' &" V. parasitica (Murr.) Rehm.'^^- â¢' .^ Pustules numerous, erumpent, at '" â~» .A^"-^^. first yellow, changing to brown at ^^a. 149.âShowing a pycnidTum of maturity; perithecia usually ten to Valsonectria and the manner iu â ' ' ^ â¢' which the spores issue from it. twenty in number, closely clustered, After Murriii. flask-shaped, deeply embedded in the stroma in the iimer bark, scarcely visible to the unaided eye; necks long, slender, curved, with thick black walls and rather prominent ostiola; asci oblong- clavate, 45-50 x 9 m, 8-spored; spores usually biseriate, hyaline, oblong, rounded at the ends, often slightly constricted, unisep- tate, 9-10 X 4-5 /i. Summer spores very minute, 1 x 2-3 n, pale-. Please note that these images are extracted from scanned page images that may have been digitally en
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