Fink: LICHENS OF NORTHWESTERN MINNESOTA. 677 
I studied the lichens of the earth and rotting wood under the 
pines with a view to establishing a formation; but the plants 
were found to be so similar to those of the C/adonza lichen for- 
mation of rotten wood and the Cladonza-FPeltigera lichen for- 
mation of shaded earth previously established that I have 
recorded them above in these formations, though possibly I 
have done violence in not separating them in this region for the 
sake of correlating results with former work in another area. 
Because of close relationship to the above formation, I shall 
next consider the U/snea formation. 
USNEA LICHEN FORMATION OF TAMARACKS IN SWAMPS 
(HENNING). 
Cetraria ciliaris (Acu.) Tuck., C. 
Evernia prunastri (L.) Acu., C. 
Usnea barbata (L.) Fr. var. florida Fr., C. 
Usnea barbata (L.) Fr. var. ceratina SCHAER. 
Usnea barbata (L.) Fr. var. dasypoga Fr. 
Usnea cavernosa Tuck., C. 
Alectoria jubata (L.) Tuck. var. chalybeiformis Acu., C. 
Parmelia physodes (L.) Acu., C. 
Parmelia olivacea (L.) Acu., C. 
Parmelia caperata (LL.) Acu., C. 
Physcia hispida (Acu.) Tuck., C. 
Calicium trichiale Acu. var. cinereum Nyt. 
The formation was afterward carefully examined at Bemidji 
and Red lake and was found to be a very characteristic one. 
At Bemidji were found all of the above-marked (C) and /rama- 
lina pusilla (Prev.) Tuck., Cetraria gunrperina (L.) Ach. var. 
- pinastrt Ach., Alectoria jubata (L.) Tuck. and Caleczum 
chrysocephalum Ach. in addition. The Red lake formation 
contained all of the species found at Bemidji except the last two, 
so that those marked (C) are the ones common to the three 
similar formations. 
The dominant elements in this formation are the Usneas, the 
£vernia and the Alectorza, which in the moist swamps and pro- 
tected on all sides by a pseudo-cortex of closely arranged 
hyphe, hang suspended or grow up from the substratum in 
fruticulose fashion. With these occur the less characteristic 
elements whose structure has been fully discussed and whose 
adaptations may be easily inferred. Though, as stated in the 
