240 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
section, the amphithecium pale or finally darkening; paraphyses distinct and rarely 
branched; asci cylindrico-clavate; spores 4-celled, ellipsoid, 14 to 23 yw long and 
6 to 9 wide. 
Fig. 17.—Pyrenula nitida. a, Portion of thallus with several immersed apothecia; 6, section through 
thallus and an inclosed apothecium to show espx cially the well developed perith»cium and the ostiole, 
a, Enlarged 3 diameters; 6, 50 diameters. From Reinke. 
Collected at Minneapolis, Mankato, and New Ulm.” On trees, especially oaks. 
Distributed throughout the United States and found also in Ontario and British 
Columbia. Known in all the grand divisions, 
3. Pyrenula leucoplaca (Wallr.) Koerb. Syst. Lich. 361. 1855. Puate 49, B. 
Verrucaria leucoplaca Wallr, in Bluff & Ping. Comp. Fl. Germ. 3: 299. 1831. 
Thallus mainly hypophloodal, but a thin whitish smooth or finely powdery layer 
sometimes appearing upon the substratum, and even when wholly hypophla@odal 
plainly indicated asa whitish coloration, oiten widely spread, rarely disappearing; apo- 
thecia minute, 0.15 to 0.4 mm. in diameter, immersed or becoming more or less super- 
ficial, globose or depressed-globose, the perithecium brownish black in section, the 
amphithecium pale or pale yellowish; paraphyses slender, simple or rarely branched; 
asci_ cylindrico-clavate; spores ellipsoid or ellipsoid-pointed, commonly 4-celled, 
14 to 24 long and 5 to 9» wide. 
Generally distributed over the State. On trees. 
Elsewhere in North America in New England, New York, Illinois, Iowa, Quebec, 
and Ontario. Known also in Europe. 
EXPLANATION OF PLATE 49.—Sce page 235. 
3a. Pyrenula leucoplaca pluriloculata Fink, Minn. Bot. Stud. 2: 709. 1901. 
Similar except that the spores are rather longer and from 4 to 8-celled. 
Common in northwestern Minnesota. On trees, usually other than poplars, on which 
the common form of the species ordinarily occurs. 
Not reported elsewhere, but Tuckerman and Koerber both mention 7-celled con- 
ditions, probably the same, and, if so, occurring at least in New England and in 
Germany. 
4. Pyrenula thelena (Ach.) Tuck. Gen. Lich. 272. 1872. 
Verrucaria thelena Ach. Syn. Lich. 92. 1814. 
Thallus hypophloodal and frequently disappearing, or indicated at the surface of 
the substratum by a whitish or yellowish coloration; apothecia immersed and 
depressed, each one indicated by a minute oblong or circular, black spot, the peri- 
thecium well developed in the upper hemisphere, there blackish brown in section, 
