674 MINNESOTA BOTANICAL STUDIES. 



found during that summer at least belong to living or to dead 

 wood formations though occasionally the plants on dead wood 

 may persist after the wood has begun to decay perceptibly at 

 the surface. 



The lichens of this formation are of the small, closely adnate 

 or hypophoeodal crustaceous type with upper cortical protection 

 in the Lecanoras and Placodiums and none in the Rinodina^ 

 the Lecidea, the Buellias and the Caliciums. The substratum 

 is a dry one usually, as I have not concluded the more damp and 

 more frequently rotting logs of the tamarack swamps, which 

 have their own peculiar formation recorded below. Hence, the 

 crustaceous type of thallus is especially adapted to the forma- 

 tion. True the Caliciums put up the minute erect podetia, but 

 these are solid cylinders of hyphae running in a longitudinal 

 direction and usually quite devoid of the algal symbionts which 

 might suffer from dryness. 



The last of the formations to be compared with those studied 

 in 1897 in southwestern Minnesota is the following. 



CLADONIA LICHEN FORMATION OF ROTTEN WOOD (BEMIDJl). 



Peltigera canina (L.) HOFFM., C. 



Peltigera canina (L.) HOFFM. var. sorediata SCHAER. 



Cladonia mitrula TUCK. 



Cladonia pyxidata (L.) FR. 



Cladonia pyxidata (L.) FR. var. neglecta (FLK.) MASS. 



Cladonia fimbriata (L.) FR. var. tubaeformis FR., C. 



Cladonia fimbriata (L.) FR. var. simplex (WEIS.) FLOT. 



Cladonia gracilis (L.) NYL., C. 



Cladonia gracilis (L.) NYL. var. hybrida SCHAER. 



Cladonia gracilis (L.) NYL. var. symphycarpia TUCK. 



Cladonia gracilis (L.) NYL. var. verticillata FR., C. 



Cladonia gracilis (L.) NYL. var. anthocephala FLK. 



Cladonia macilenta (EHRH.) HOFFM. 



Cladonia bacillaris NYL. 



Cladonia cristatella TUCK. 



Comparing this formation with the corresponding ones at 

 Mankato and Granite Falls,* we find that the formations are 

 constant at least as regards genera, the one herein recorded for 

 a region, especially rich in Cladonias, being of course richer in 

 species than the two formerly studied. The addition of a third 



*Fink, B. 1. c., 306-307. 



