FINK——THE LICHENS OF MINNESOTA. 159 
PELTIGERA Willd. Fl. Berol. Prodr. 347. 1787. 
Puate 29. 
The thallus is foliose, more or less lobed and rather loosely attached to the sub- 
stratum. The common color is sea-green varying toward brown. The structure is 
peculiar in the total absence of a lower cortex, while there is a well developed upper 
one. The algal layer is in the usual position just below the cortex, and the portion 
of the thallus below the algal layer is somewhat differentiated, in that the hyphe of 
the lower portion run in a somewhat horizontal direction and together with the usually 
numerous rhizoids serve for support and also for protection against too rapid evapora- 
tion of moisture, thus functioning somewhat like a true cortex. The plants are 
usually more or less veined below. in some of the species the upper surface is more 
or less clothed with hyphx, which give a downy appearance and which are structurally 
and functionally comparable to the trichomes of higher plants. These hyphz have 
thick walls, and the cells are short. The algal symbiont is doubtless nearly always 
Polycoccus or Dactylococcus, though the chains of cells can hardly be discerned. 
In one of our species cephalodia occur on the upper surface of the thallus. 
The apothecia are usually orbicular, and are found on the margins of the lobes of 
the thallus. They are usually immersed in the lobes and present somewhat the 
appearance of those of Heppia and Solorina. The hypothecium is pale or slightly 
colored. The hymenium is commonly brownish above. The paraphyses are com- 
monly simple, though branched forms may be found in all of the species. The spores 
are fusiform or acicular, 4 to 8-celled, hyaline, or brownish, and frequently more or 
less curved. 
Notwithstanding the absence of a lower cortex, there is a somewhat close relation- 
ship between the present genus and Nephroma and Sticta. 
Eight species occur in the State, and one of them is represented by five distinct 
forms. Qn earth or more rarely on old wood or rocks. 
Type species Peltigera aphthosa (1..) Willd. loc. cit. 
EXPLANATION OF PLATE 29.—Cephalodia of Peltigera aphthosa. Fig. 1, a, a young cephalodium; 0, the 
trichomatie hyph holding the cephalodium. Fig. 2, an older cephalodium, a, the internal hyphe and 
algal cells; b. the well-developed cortex; ¢c, the supporting trichomatic hypha. Fig. 3, a mature cephalo- 
dium; a, the internal hyph and algal cells; b, the upper cortex; c, the lower cortex; d, the supporting 
hyphie; e, the thallus below the cephalodium, where the algal cells have disappeared and the cortex is 
transformed into hyphal tissue; f, the cortex; g, the algal layer of the supporting thallus. Fig. 1, enlarged 
about 100 diameters; fig. 2, enlarged 400 diametzrs; fig. 3, enlarged 200 diameters. From Schneider. 
KEY TO THE SPECIES. 
Thallus cephalodia-bearing above............-.-----------+--- L. P. aphthosa. 
Thallus not cephalodia-bearing above. 
Thallus devoid of trichomatic hyphe above. 
Thallus lobes small and roughly fan-shaped. .......... 2. P. venosa. 
Thallus lobes larger, not fan-shaped. 
Apothecia-bearing lobes more or less digitately 
clustered; spores 4 to 8-celled, elongated. .... 4. P. polydactyla. 
Apothecia-bearing lobes not digitately clustered; 
spores 4-celled, much shorter. ........-.----- 3. P. horizontalis. 
Thallus having trichomatic hyphe above. 
Margins of the lobes frequently isidioid-granulate, lobu- 
late or sorediate. .....-..2------2------222------ 5. P. seutaia. 
Margins not isidioid and not lobulate or sorediate. 
Lower surface of the thallus partly or wholly brown- 
ish or blackish. 
Apothecia orbicular............------------- 6. P. malacea. 
Apothecia oblong or revolute. ...........-.-- 7. P. rufescens. 
