102 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
genus and reminds one of that of Toninias and also of the primary thallus of most 
Cladonias. Thus the genus seems to be related below with Lecidea and above with 
Cladonia, probably having been derived from members of the former genus and _per- 
haps leading up to certain ones of the latter. 
Five species and subspecies occur in the State. Commonly on-earth or rocks. 
Type species Psora caesia Hoffm. loc. cit. But this is a Physcia, doubtless P. 
caesia (Hoffm.) Nyl. This, therefore, gives Psora precedence over Physcia, but Psora 
Hoffm. is anticipated by Psora Hill, 1769, a genus of Asteraceae. 
EXPLANATION OF PLATE 9.—Fig. 1, a, a portion of the thallus; b, an apothecium. Fig. 2, a, an apo- 
thecium; 5, a portion of the thallus. Fig.3,asection through an apothecium and the underlying thallus; 
a, the hymenium; 6, the hypothecium; c, the medullary layer; d,the hyphal rhizoids. Fig. 4,a section of 
the thallus; a, the dermis; b, the upper cortex; c, the algal layer; d, the medullary layer; ¢, the hyphal 
rhizoids. Fig. 5,a paraphysis and anascus. Fig. 6, free simplespores. Fig. 1, natural size; fig. 2, enlarged 
about 8 diameters; fig. 3, enlarged 300 diameters; fig. 4, enlarged about 425 diameters; figs.5, 6, enlarged 
650 diameters. From Schneider. 
KEY TO THE SPECIES. 
Thallus brownish to blackish; on rocks. . 
Thallus brownish olivaceous and darker, ascendant........ 1. 
P. rufonigra, 
Thallus dull brown to reddish brown, white-edged, adnate, 
or ascendant at the margin..............-2---.----.--.- 2. P. russellit, 
Thallus not brownish or blackish; on earth, 
Thallus white, adnate...........2...2..... Cee ee eee eee 3a. P. decipiens de- 
albata. 
Thallus not white. 
Thallus incarnate brick-colored, closely adnate, white- 
edged... 2.222222 ee eee 3.) O&P. 
Thallus greenish yellow or finally tawny..........-..-- 4. P. 
we 
decipiens. 
icterica, 
-) 
1. Psora rufonigra (Tuck.) Fink. 
Biatora rufonigra Tuck. Syn. Lich. N. E. 58. 1848. 
Thallus composed of brownish or more commonly olivaceous or even blackish, 
scattered or more or less clustered and imbricate, irregular or round-lobed, commonly 
ascendant, somewhat concave, smooth squamules, these rather small, 0.5 to 1.5 mm, 
in diameter, commonly darker along the margins and below, clothed below with 
dark hyphal rhizoids; below the algal layer of the thallus a layer of densely inter- 
woven hyphe, to be regarded as a pseudocortex rather than a medulla; apothecia 
rather small, 0.3 to 1 mm. in diameter, adnate, in ours at least black, though said to 
be sometimes dark rufous, rarely flattish and margined by an exciple, but more com- 
monly convex and immarginate; hypothecium pale; hymenium pale or darkening, 
especially above; paraphyses simple or rarely branched, commonly dark and en- 
larged toward the apex; asci clavate; spores oblong-ellipsoid, 8 to 15 » long and 5 to 
7 » wide, 
The plant is the most widely distributed member of the genus in the State, and may 
be looked for in all portions except the southeastern. On the Archeean or Algonkian 
rock exposures. Though the most widely distributed, this lichen is by no means 
common. Thus far, in Minnesota, it has always been met with growing on rocks with 
an alga resembling Sirosiphon in external appearance. 
The species is widely distributed in the United States and extends northward into 
British America. <A strictly North American plant. 
Biatora rufonigra of the preliminary reports. 
2. Psora russellii (Tuck.) Fink. PLATE 9. 
Lecidea russellii Tuck. Proc. Amer. Acad. 5: 417, 1862. 
Thallus composed of rather thick, dull or reddish brown, scattered or more or less 
clustered, closely adnate or marginally ascendant, rounded or more or less lobed and 
