PLOWKIGHTIA. 



231 



Plowrightia morbosa (Sch.) (Britain and U.S. America). 

 Black-knot of the plum tree.-' In America this is a very 



Fig. 115. — Plowrightia mor- 

 bosa. Ascus, with eight 

 spores. Spores in germina- 

 tion. Filamentous para- 

 physes. (Cop. from Farlow. ) 



Fig. 114. — Plowrightia morbosa. (v. Tubeuf phot.) 



injurious and widely distributed disease of various species of 

 Prunus, especially plum and cherry. The living branches and 

 twigs become coated with a crust of warty excrescences, and 

 at the same time are more or less thickened and deformed. 

 A mycelium permeates the tissues of those swollen twigs, and 

 forms black crusty stromata in which the perithecia are 

 embedded. The perithecia contain simple paraphyses and eight- 

 spored asci. The spores consist of a larger and a much smaller 

 cell. (Pycno-conidia are produced frequently in artificial culture, 



'Farlow, Bvlletin Bussey Institution, Part v., 1876. 

 Humphrey, Anniml Eeport of Mass. Exper. Station, 1890. 

 Lodeman (Cornell Univ. Exper. Station, Bulletin JN'o. 81, 1894) gives 

 general account of Black-knot and a Bibliography. 



