680 MINNESOTA BOTANICAL STUDIES. 
The following formation was distinctly discernible in the low 
woods about the tamarack swamps near Henning, the species 
composing it being unusually abundant. From the frequence 
of Pertusarzas rare elsewhere in-the region studied during the 
summer, I shall name it as follows: 
PERTUSARIA LICHEN FORMATION OF TREES IN LOW WOODS 
(HENNING). 
Physcia obscura (Enru.) Nyu. 
Collema flaccidum Acu. 
Collema nigrescens (Hups.) Acu. 
Leptogium myochroum (EuruH., SCHAER.) TUCK. 
Pertusaria velata (TurN.) NyL. 
Pertusaria pustulata (Acu.) Nyt. 
Biatora glauconigrans Tuck. 
Biatora rubella (EuRH.) RAs. 
Biatora varians (Acu.) Tuck. 
I failed to find such a formation elsewhere in the territory 
explored. The plants in the formation grow on the common 
deciduous trees of the area, whereas at Bemidji and Red lake 
the swamps were surrounded for the most part by pines. Asa 
whole the various adaptations of the plants are not difficult to 
detect. It is a little peculiar that the species of Physcza, be- 
longing to this damp formation, belongs to the section of the 
genus having a well developed parenchymatous cortex rather 
than to the one having a non-cellular cortex of closely packed 
hyphe. The Collemas with their non-cortical thallus and the 
Leptogium with a cortex of a single layer of cells are, of course, 
quite at home in such a damp habitat, as are the Bzatoras with 
their thallus devoid of cortex. The Pertusarzas have a fairly 
developed upper cortex. 
The last formation to be recorded is a scattered one detected 
in shaded places at Bemidji, which may be designated as 
follows : 
BIATORA LICHEN FORMATION OF MOSSES (BEMIDJI). 
Pannaria languinosa (Acu.) Kr. 
Biatora vernalis (L). Fr. 
Biatora spheroides (Dicxs.) Tuck. 
Biatora hypnophila (Turn.) Tuck. 
