FINK—THE LICHENS OF MINNESOTA. 187 
claims when we consider the close structural relationship of the apothecia of a large 
number of Pertusarias with those of the Trypetheliums, not represented in our flora. 
In placing the present family next to the Lecanoraceae, it is only fair to admit this 
other perhaps equally close relationship. 
The crustose thallus, the nature of the algal symbiont, the peculiar grouping of the 
apothecia in verruce of the thallus (the grouping quite Trypethelium-like), and the 
large size of the spores all receive attention in the description of the genus. 
PERTUSARIA Lam. & DC. FI. Fr. ed. 3. 2: 319. 1805. 
The thallus is strictly crustose. In one or two species, however, a poorly developed 
upper cellular cortex can be made out. In others there is a thin upper pseudo- 
cortex of interwoven hyph, which are frequently gelatinized into a structureless 
layer, The algal and medullary layers are frequently well differentiated, but in none 
of our species is any suggestion of a lower cortex found. Hyphal rhizoids serve as 
attaching organs after the manner of crustose thalli in general. The thallus varies 
considerably in thickness, and in at least one of our species it is mainly hypophloodal. 
Sea green and ashy are the common colors. The algal symbionts are Cystococcus, 
and the algal cells are quite uniform in the different species, apparently scarcely 
modified by their association with the fungal symbionts. 
The apothecia are small or minute, commonly globose and immersed in the eleva- 
tions or verruce: of the thallus, often a half dozen or more in a single verruca. The 
apothecium commonly opens by a small pore, which is not always evident except in 
sections cut through it. However, in some of the species the apothecia or the verruce 
become open and disk-like, or rather the globular structure becomes depressed, for 
the thallus which always covers the structure either remains intact or breaks up into 
a sorediate mass. The paraphyses are commonly more or less branched and hyaline 
throughout. The hypothecium and hymenium are pale, or the latter sometimes 
brownish above. The asci are clavate, cylindrico-clavate, or variously irregular, with 
rather thick walls. The spores are hyaline or pale, very large and simple, though 
some authors admit 2-celled forms. There are from | to 8 spores in each ascus, and 
the spore walls are quite thick. 
The relationships of the genus are by no means certain. The thallus structure and 
the spores look toward Lecanora and allied genera. The very presence of what may 
be regarded a perithecium would seem to indicate a close relation to Pyrenula and 
Trypethelium. However, the so-called perithecium is here quite a different struc- 
ture, and the thallus is much better developed and commonly epiphleodal. Tucker- 
man gives one view of relationships clearly in his genera. Seven species and sub- 
species occur in the State. On trees and rarely on rocks, 
Type species Pertusaria communis DC. loc. cit. 
KEY TO THE SPECIES. 
Thallus usually lighter-colored or zonate toward the circum- 
ference, 
Thallus usually becoming rough. 
Spores 130 to 250 « long, one in each ascus............ lL. P. velata. 
Spores 75 to 150 » long, one or two in each ascus....... 2. P. multipuncta. 
Thallus smooth and thin; spores as in the last above....... 2a. P. multipuneta 
ophthalmiza. 
Thallus scarcely lighter-colored or zonate toward the circum- 
ference. 
Apothecia 2 to several in each verruca; spores 100 to 180 
long, | or 2in each ascus......2...0.02.22.22.22--.--- 3. P. communis. 
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