FINK—THE LICHENS OF MINNESOTA. 191 
merely being more or less indented. Soredia and isidioid growths are quite common 
on the upper surface of the thallus, largely replacing apothecia as reproductive bodies. 
The upper and the lower cortical layers are cellular and well developed. The algal 
layer is in the usual position for dorsiventral thalli, viz, just below the upper cortical 
layer. The medullary tissue consists of the usual loosely interwoven hyphe, and in 
some species the lower portion of this tissue is very loosely interwoven and contains 
large air spaces. Rhizoids are usually present on the lower surface of the thallus, and 
cilia frequently occur along the margins or on the upper surface. Spermagones are 
conspicuous. 
The apothecia are sessile or subpedicellate on the upper surface of the thallus, the 
thalloid margin is usually entire or more or less crenate, the disk is usually brown and 
often deeply concave, the hypothecium is pale or slightly colored and frequently 
shows two distinct layers, the hymenium is pale or yellowish or brownish tinged. The 
paraphyses are usually simple and slender, and the spores are simple, hyaline, and 
much alike in form and size in the different species. Apothecia are very rare in more 
than half of our species. 
In appearance and structure of the thallus the genus seems near to Physcia, but 
when we take into consideration the spore characters, doubtless the relationship with 
Cetraria is closer. The relation between the present genus and the higher simple- 
spored Lecanoras with foliose thallus is also close. Parmelia seems to stand between 
Lecanora and Cetraria. 
The genus is represented in Minnesota by no less than 22 forms and is the largest of 
our foliose genera. 
Parmelias occur on trees, old wood, rocks, and rarely on the earth or over mosses. 
Type species Parmelia elacista Ach. op. cit, 159. pl. 4. f. 4. But this is a Lecanora 
(L. elacista), and the generic name Parmelia would take precedence over Lecanora. 
See note under Gyalecta. 
EXPLANATION OF PLATE 35.—Fig. 1, a, apothecia; 6, the thallus. Fig. 2, a section of an apothecium 
and the thallus below; a, the hymenium; 6 and c, the hypothecium; d, the algal layer; e, the medullary 
layer; f, a lower algal layer; 9, the lower cortex. Fig. 3, a section of the thallus; a, the upper cortex; b, 
the algal layer; c, the medullary layer; d, the lower cortex. Fig. 4, paraphyses and anascus. Fig. 5, free 
simple spores. Fig. 6, algal cells, haustoria, and hyphe. Fig. 1, natural size; figs. 2 and 3, enlarged 400 
diameters; figs. 4, 5, and 6, enlarged 650 diameters. From Schneider. 
KEY TO THE SPECIES. 
Thallus never sea-green. 
Thallus straw-colored. 
Thallus large, with short, wide lobes; commonly on 
0.6 13. P. caperata. 
Thallus smaller, or with longer, narrower lobes; com- 
monly on rocks, 
Thallus medium-sized or larger, with long, narrow 
lobes......----- 2202002 eee eee teers 14. P. conspersa. 
Thallus quite small, the center often falling away. 15. P. centrifuga. 
Thallus olivaceous. 
Apothecia absent in ours; a larger plant than the next, 
less closely adnate and isidioid or sorediate.......... 12. P. conspurcata. 
Apothecia present, at least usually. 
Thallus lobes and the exciple densely covered 
with minute verruce.......---------+--+--+++-- lla. P. olivacea aspi- 
dota. 
Thallus lobes and exciple not verruca-bearing. 
Thallus lobes much crowded and imbricated,; 
on rocks.....-.--.---222-- 200000 eee eee lib. P. olivacea pro- 
lixa. 
Thallus lobes not much crowded and imbri- 
cated; on wood........--------+-+++-+--+-° ll. P. olivacea, 
