76 



MORPHOLOGY 



Black fungi. — This (Pyrenomycetes proper) is an exceedingly large 

 and varied group, characterized by a flask-shaped ascocarp opening at 

 the top (perithecium) and lined by the hymenial layer of asci and hair- 

 like paraphyses (fig. 184). It includes parasites on various parts of 

 plants, especially cortex and leaves; and also saprophytes on decaying 

 wood, etc., often forming black spots, knots, etc., resembling charred 

 places and suggesting both the technical and common names. The peri- 

 thecia arise either singly on the mycelium (as in Plowrightia), appearing 



181 Ijy 182 



Figs. i8t, 182. — Mildews: 181, ascocarp of Microsphaera, showing the heavy case, 

 dichotomous appendages, and asci crushed out of the case; 182, ascocarp of UnciniUa, 

 with hooked appendages. 



as small black dots irregularly scattered, as in the mildews; or they occur 

 in groups embedded in a variously shaped mass of compact (paren- 

 chyma-like) mycelium, the whole structure being known as the stroma 

 (pi. stromata). A single illustration of each kind will be given. 



Black knot {Plowrightia morhosa). — This is a destructive disease 

 that attacks the plum and cherry (fig. 1 100). In the spring the mycelium 

 is under the bark; then it breaks through, beginning the knot, which 

 may become quite large and solid, composed of the mycelium of the 

 parasite and hypertrophied host tissue. Numerous sporophores arise 

 from the mycelium, abstricting conidia ; and in the autumn the perithe- 

 cia appear over the surface of the knot as small papillae, open at the top 

 and lined with a hymenial layer. In the following spring the ascospores 

 escape and begin fresh infections. 



