THE ASCOMYCETES OF OHIO V 
355 
pound rhizoids; apothecia of considerable size, commonly on extended 
lobes, usually imbedded in the tissues on the upper side, or more rarely 
on the lower side; exciple inconspicuous; hypothecium usually light or 
darker brown; hymenium usually pale below and brown or tinged brown 
above; paraphyses simple or branched, distinct, seldom gelatinized or 
coherent; spores hyaline or brown, 4- to several-called, elongated. 
KEY TO THE GENERA 
1. Cortex developed on the upper side of thallus only, 
spores hyaline.Peltigera. 
2. Cortex developed on both upper and lower sides of 
thallus, spores brown.Nephroma. 
Peltigera Willd. FI. Berol. Prodr. 347. 1787. 
Thallus foliose, usually adnate toward the center, with the lobes more 
or less ascending at the margins, green-gray varying toward brown, the 
upper surface sometimes bare, or again clothed with trichomatic hyphae, 
giving it a downy appearance, or bearing cephalodia or isidioid branchlets, 
the lower surface usually conspicuously veined, with tufted -rhizoids 
descending from the veins, color of these light or dark; cross section 
showing two distinct layers, the upper plectenchymatous cortex composed 
of 2 to 4 layers of meshes, and the medulla, composed of densely interwoven 
and irregularly disposed hyphae; lower cortex lacking, but the hyphae of 
the lower portion in some instances more or less horizontally arranged and 
produced into hyphal rhizoids, thus serving for support and protection 
much like a true plectenchymatous cortex; apothecia usually orbicular, 
frequently revolute, imbedded in the upper surface of the lobes; exciple 
plectenchymatous (Fig. 4); hypothecium of interwoven hyphae, usually 
tinged brown; hymenium commonly pale below and brown above; par¬ 
aphyses usually simple, but some branched ones present in all of the 
species, hyaline in the main, but usually enlarged and tinged brown at the 
apex; asci usually cylindrico-clavate; spores hyaline, fusiform to acicular, 
sometimes curved, 4 to 8-celled, 8 arranged parallel in the asci. 
The algal host cells lie in the medulla, just below the upper cortex. 
2. P. 
KEY TO THE SPECIES OF PELTIGERA 
Upper surface of the thallus bearing cephalodia 
Upper surface of the thallus devoid of cephalodia. 
Thallus bearing trichomatic hyphae above. 
Upper surface bearing isidioid branchlets or lobules 
Upper surface devoid of isidioid branchlets or lobules. 
Orbicular sorediate areas on the upper surface of the thallus 3 
Soredia lacking on the upper surface. 
Lower surface of the thallus of light color 
Lower surface partly or wholly dark 
Thallus devoid of trichomatic hyphae. 
Apothecia orbicular and revolute, spores 4-to 8-celled 
Apothecia usually transversely oblong, spores 4-celled 
1. P. aphthosa 
5. 
6. P. 
7. P. 
praetextata 
P.sorediata 
4. P. canina 
P. rufescens 
polydactyla 
horizontalis 
