232 ILLINOIS ACADEMY OF SCIENCE 
MYCELIUM 
The mycelium in newly invaded tissue is slender and hya- 
line. In the course of development it becomes amber-yellow 
and later dark-brown, filling the leaf tissue with a net-work 
of hyphae, which encloses in its meshes what remains of the 
broken down host cells. The mycelium is septate and branched, 
although not profusely so. It varies in thickness from 1.5 p» 
to 4.5 » and in a later stage of development sometimes forms 
short and comparatively thick, irregularly shaped cells. 
PERITHECIA 
The perithecia are embedded in the stromata and consist of 
immersed cavities, subglobose or angled by mutual pressure. 
They are scattered in the stromata or closely aggregated, 
thirty being the maximum number in a single stroma. An 
apparent wall surrounds the loculus made up of dark brown 
mycelium and bearing at the tip a small ostiole. The ostiole 
is usually concealed by the epidermis. The perithecia open on 
both upper and lower surfaces of the leaf, contiguous ones in 
the same stroma sometimes have the ostiole on opposite sur- 
faces of the leaf. The diameter of the perithecia parallel with 
the surface of the leaf varied from 171 » to 352 wu. The vertical 
diameter of the perithecia is much greater than the length of 
the asci, since they reach up into the perithecial cavity only to 
about one-third of its height. Long paraphyses extend from 
the base toward the center of the cavity. 
ASCI 
The asci are numerous. They are cylindrical and vary in 
length from 64.8 » to 91.8 », and in thickness from 7.2 » to 
10.8 », with a stipe 9 » to 20 p» in length. 
PARAPHYSES 
Copious paraphyses are present extending far beyond the 
asci as they sometimes reach a length of 125 ». They are fili- 
form or attenuate from a somewhat thickened base. 
