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, appearing as small black 
181 g/2r 182 
FIGS. 181, 182. Mildews: 181, ascocarp of Micros phacrj, showing the heavy case, 
dichotomous appendages, and asci crushed out of the case; 182, ascocarp of Uncinula, 
with hooked appendages. 
dots irregularly scattered, as in the mildews; or they occur in groups 
embedded in a variously shaped mass of compact (parenchyma-like) 
mycelium, the whole structure being known as thestroma (pi. stromata). 
A simple illustration of each kind will be given. 
Black knot (Plowrightia morbosa). 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. 
