FINK—THE LICHENS OF MINNESOTA. 215 
7. Placodium cerinum (Hoffm.) Hepp, Spor. Flecht. Eur. pl. 46. f. 405. 1857. 
Puate 44, B. 
Patellaria cerina Hoffm. Descr. Pl. Crypt. 2: 32. pl. 33. f. 1. 1794. 
Thallus crustose, suborbicular and of medium size, 15 to 55 mm. in diameter, or 
becoming irregular and more widely spread over the substratum, rarely disappearing, 
thin, smoothish and chinky or thicker and verrucose or sometimes becoming sub- 
areolate, ashy or varying toward whitish or more commonly toward lead-gray, an 
upper cortex scarcely distinguishable; apothecia small to nearly middle-sized, 0.3 to 
1.2 mm. in diameter, sessile or possibly sometimes subsessile, the disk flat, waxy- 
yellow varying toward reddish or olivaceous-brown, the exciple thalloid and entire, 
of the same color as the thallus, whitish or sometimes of the color of the disk, sometimes 
becoming flexuous; hypothecium pale; hymenium pale beneath and yellowish or 
brownish above; paraphyses simple or branched, commonly more or less enlarged 
and colored toward the apex; asci clavate; spores ellipsoid, polar 2-celled, 10 to 18 
long and 6 to 10 » wide. 
The plant is quite variable, and a large number of subspecies have been recognized. 
One of ours, however, seems to differ from all of these, and we venture to give it a 
name, Another form with evanescent thallus and closely clustered, rather flexuous, 
olivaceous-brown apothecia was collected on old pine wood at Red Lake. Finally, 
one of the two subspecies admitted by Tuckerman, it seems to us, must be separated. 
Generally distributed over the State. On trees and rarely on old wood. 
Found throughout North America. Known also in all of the grand divisions. 
EXPLANATION OF PLATE 44.—See page 213. 
Va. Placodium cerinum ulmorum Fink, Proc. lowa Acad. Sci. 11: 143. 1904. 
Thallus of moderate thickness, granulose-verrucose, ashy or sea-green, irreguarly 
spread over the substratum usually in small patches; apothecia of the usual size, 
the disk dull waxy yellow, roughened and more or less pruinose, the exciple promi- 
nent, ashy-whitish, entire or more commonly subcrenulate or radiately striate. 
Generally distributed over the southern half of the State. On elms and rarely on 
other trees, especially oaks. 
The subspecies is common in Iowa and has been collected in Kansas by E. Bar- 
tholomew. The Kansas material was on red cedar bark. 
7b. Placodium cerinum sideritis Tuck. Syn. N. A. Lich. 1: 175. 1882, 
Thallus thickened, composed of contiguous, scaly, and frequently convex verruce 
or areoles, of the same color as the last (said by Tuckerman to be iron-gray); apothecia 
adnate or rarely immersed, rather smaller, the disk nonpruinose, yellowish rust- 
colored, or in ours becoming darker and even black, the exciple of the color of the 
thallus and sometimes disappearing; spores rather smaller. 
Doctor Zahlbruckner considers part of ours a new species, but gives no name. 
Considered by Tuckerman as a strictly North American form, and the differences 
as to thallus and the adnate or immersed apothecia would seem to indicate a new 
species rather than a subspecies of the above species. Some other disposition of all 
or part of our material will doubtless need to be made. 
Generally distributed over the State. On rocks other than calcareous. 
A strictly North American plant. Elsewhere known in New England, Virginia, 
Illinois, and Towa. 
8. Placodium pyraceum (Ach.) Fink. 
Parmelia cerina pyracea Ach. Meth, Lich. 176. 18038. . 
Thallus very thin and ashy-whitish, smooth or granulate-scurfy, evanescent; 
apothecia small or minute, 0.2 to 0.6 mm, in diameter, sessile or rarely adnate, fre- 
quently numerous, clustered, angulate and obscuring the thallus, the disk flat or 
convex, yellowish-orange, the thalloid exciple thin and yellowish or whitish, evan- 
escent, and the apothecia, as commonly seen, biatoroid, with thin proper exciple, 
