148 



Mycologia 



the host cells below is composed of small thin-walled cells. 

 Above this is to be found a dark layer composed of rather larger, 

 polyhedral cells. This becomes thinner toward the margin which 

 would appear to offer a favorable place for the pycnidium to 

 rupture, but so far as observed marginal dehiscence does not 

 occur. Above the middle layer lies that from which the conidio- 

 phores originate. It is composed of small, thin-walled, colorless 

 cells (pi. 9, fig. 16). 



Fig. 2. a. Sporophores of Sclerotiopsis concava. X 700. b. Spores morn 

 highly magnified. X 1200. 



In mature pycnidia the sporophores form a palisade-like layer 

 covering the base of the pycnidium. They are 10-20 X I \h f re_ 

 quently with short lateral branches (text- fig. 2). The spores are 

 hyaline or faintly chlorine colored 6-9 X 1-5-2 /x. In old rup- 

 tured pycnidia the spores in mass may approach olivaceous. They 

 are borne apically on the terminal and lateral branches, some- 

 times slightly adhering in chains as noted by Massalongo ; but not 

 ordinarily found in that condition as the spores usually separate 

 as fast as they mature. They are boat-shaped, curved, acute, 

 oblique-angled, convex on one side, slightly concave on the other. 

 In keel view they are fusoid. 



No ostiole is formed and the dehiscence of the pycnidium is 

 often delayed until spring. It may occur, however, within a few 

 weeks after maturity if the weather is very moist. The rupture 

 of the epidermis should not be confused with the splitting of the 

 wall of the pycnidium. In oblong forms on small branches, the 

 rupture may extend in a single line from end to end (pi. 9, figs. 

 14, 15). In the circular types there are usually three or four 

 cracks extending from the center toward the margin. The an- 



