58 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
0.2 mm. in diameter or in the short dimension of the elongated forms; hypothecium 
pale or pale brownish; hymenium pale; paraphyses scarcely differing from the hyphee 
of the thallus; asci pyriform or subpyriform; spores 4-celled (or rarely 5 or 6-celled), 
solezeform, 15 to 22 » long, 4.5 to 7 » wide. 
Generally distributed over the State. On trees and confined to smooth bark.. A 
number of subspecies have been recognized based on the number of cells i in the spores 
and the form of the apothecia. 
Distributed throughout North America, except possibly the extreme north. Also 
well known in Europe and Asia. 
6. Arthonia radiata (Pers.) Ach. Lich, Univ. 144. 1810. PLATE 2, B. 
Opegrapha radiata Pers. Ann. Bot. Usteri 7: 29. 1794. 
Thallus sea-green varying toward whitish or brownish, partly or wholly hypo- 
phloeodal and rarely entirely dying away, occurring in more or less irregular patches, 
reaching 5 to 30 mm. in diameter and rarely bordered wholly or in part Ly a dark 
line, the thalli frequently running together and covering much larger areas of the 
substratum; apothecia stellate, difform, or ramose, adnate or more commonly im- 
mersed, rarely erumpent, black, plane or slightly convex, rather large for the genus, 
0.4 to 1.5 mm. in the longest dimension; hypothecium pale brown; hymenium pale 
or brownish; paraphyses simple or branched, with enlarged brownish apex; asci 
broadly clavate or subpyriform; spores 4-celled, solezeform, 12 to 20 » long and 4 to 
6 » wide. 
Generally distributed over the State. On trees, confined to smooth bark and 
usually to rather young trees. ot 
The plant is widely distributed in North America and is general in its foreign dis- 
tribution also. Several subspecies are recognized, few of which seem to have any 
value. 
EXPLANATION OF PLATE 2.—See page 55. 
6a. Arthonia radiata swartziana (Ach.) Willey, Syn. Arth. 44. 1890. 
Arthonia swartziana Ach. Neu. Journ, Bot. Schrad. 1°: 13. pl. 4.f. 1. 1806. 
Apothecia larger and more commonly rounded; spores also rather larger. 
What seems to be this subspecies was collected in the northern portion of the State 
at Rainy Lake City and at Tower. Habitat same as that of the species. 
Widely distributed in the United States and British America. Also known in 
Europe and Africa. 
ARTHOTHELIUM Mass. Ric. Lich. 54. f. 101. 1852. 
Like Arthonia, the genus has a rudimentary thallus without cortical tissues. But 
the thallus is on the whole better developed than in the foregoing genus, commonly 
becomes largely or wholly epiphloeodal, and rarely, if ever, entirely disappears. It 
is frequently quite thick and uneven and rarely even areolate. The algal symbiont 
is Chroolepus, at least so far as has been ascertained. 
The apothecia are adnate, or more or less sunken in the thallus or substratum. 
They are usually small and rounded or irregular in outline. The color is black or 
rarely brownish black. The hypothecium is usually brown, though it may vary to 
dark brown or pale. The hymenium is pale to brown. The paraphyses are usually 
much branched, but are quite commonly simple in some species. The asci are usu- 
ally of the peculiar pyriform or subpyriform shape. The spores are many-celled and 
muriform, large in size, and still quite constantly 8 in each ascus, and they may be 
‘hyaline, pale, or brown in color. 
The genus is closely related to Arthonia as to structure of thallus and yet more as 
regards the apothecia. Though the spores are usually quite different and apparently 
