FINK—THE LICHENS OF MINNESOTA. 139 
In the United States southward to Maryland and westward to Iowa. Also known in 
Canada. Found also in Europe and Africa. 
7. Collema pustulatum Ach. Syn. Lich. 317. 1814. 
Thallus suborbicular or irregular and scattered, small, scarcely exceeding 10 to 
18 mm, in diameter in ours, the lobes becoming long and narrow and subdichotomously 
many-cleft or more irregularly divided, or even shorter and subentire, frequently 
ascending or suberect; more closely attached portions of the thallus usually dying 
and leaving the commonly ascending lobes separately attached to the substratum, 
thus giving the scattered appearance, the rhizoids few ; in color, brownish olivaceous 
or darker, and scarcely lighter beneath; algal cells somewhat more numerous toward 
the surfaces, especially the upper in the closely adnate portions; apothecia small and 
appearing like pustules on the thallus-lobes, 0.2 to 0.7 mm. in diameter, immersed or 
adnate, the disk brown, reddish or darkening, flat or concave, frequently deeply 
sunken in the entire thalloid margin; hypothecium pale; hymenium pale below and 
brownish above; paraphyses simple or rarely branched, commonly enlarged and 
brownish toward the apex; asci clavate; spores ovoid-ellipsoid, hyaline or pale, 4-celled 
and becoming muriform, 13 to 24 » long and 10 to 13 » wide. 
Collected on calcareous rocks at Mankato. 
Known from such rocks in Pennsylvania, Alabama, Illinois, and Iowa, and extend- 
ing westward to the Pacific coast in British America. A strictly North American 
plant. 
LEPTOGIUM Ach.; 8. F. Gray, Nat. Arr. Brit. Pl. 1: 400. 1821. 
PLATE 22. 
The thallus is foliose and commonly orbicular, macroscopically appearing quite 
similar to that of Collema, but differing microscopically in that there is a cortex. 
This structure commonly consists of a single layer of cells, both above and below. 
The cortex makes the thallus somewhat more rigid than that of Collema, and renders 
the plants as a whole less gelatinous. In some of the species there is a rather poorly 
defined algal layer just below the upper cortex and somewhat of a medullary layer 
below this, but as a rule these layers can not be distinguished, though the algal chains 
are quite commonly more numerous toward the upper surface. These chains are 
hardly so long as in the last two genera. Rhizoids are rare, though clusters of simple 
ones may be found occasionally in any species at points where the thallus is closely 
attached. The thallus is partly attached by them, but for the most part simply 
adheres directly to the substratum. A single species, however, has numerous well- 
developed rhizoids, and this is sometimes separated from the genus, 
The apothecia are quite common in some of the species, but seldom seen in others. 
The exciple is typically thalloid, but the algal cells may rarely disappear; or the 
exciple itself more rarely may be overgrown by the expanding disk and the whole 
structure of the apothecium become essentially biatoroid. The color of the disk is 
commonly some shade of brown, and it is usually flat or concave. The hypothecium, 
hymenium, and paraphyses are all much as in Collema. The spores of the species 
here admitted to the genus are pale and more or less muriform. Tuckerman admits 
plants having less highly developed spores, but his genus should doubtless be divided 
as it has been by some other authors. 
The close relation of the present genus to Collema is apparent. The structure is 
somewhat higher in Leptogium. 
Seven forms have been noted in the State. The habitats are similar to those of 
Collemas, but as a whole the plants are less confined to moist places. 
Type species Leptogium tremelloides (L.) 8. F. Gray, loc. cit. 
