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 Cladonia lichen for- 

 mation of rotten wood and the Cladonia- Pelt iger a 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 Usnea formation. 



USNEA LICHEN FORMATION OF TAMARACKS IN SWAMPS 

 (HENNING). 



Cetraria ciliaris (Acn.) TUCK., C. 



Evernia prunastri (L.) ACH., 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 ACH., C. 



Parmelia physodes (L.) ACH., C. 



Parmelia olivacea (L.) ACH., C. 



Parmelia caperata (L.) ACH., C. 



Physcia hispida (Acn.) TUCK., C. 



Calicium trichiale ACH. var. cinereum NYL. 



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 juniperina (L.) Ach. var. 

 pinastri Ach., Alectoria jubata (L.) Tuck, and Calicium 

 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 

 Evernia and the Alectoria, which in the moist swamps and pio- 

 tected on all sides by a pseudo-cortex of closely arrar ged 

 hyphae, hang suspended or grow up from the substrati ,n in 

 fruticulose fashion. With these occur the less charac eristic 

 elements whose structure has been fully discussed ar . whose 

 adaptations may be easily inferred. Though, as st?' d in the 



