716 MINNESOTA BOTANICAL STUDIES. 



(8) The scarcity of Cladonias, as regards individuals and earth 

 growing species, I have not yet attempted to explain. If 

 general scarcity is due to dry climate, one would suppose 

 that the earth forms should predominate. Yet, I suspect 

 that the old stumps and the Saint Peter sandstone fur- 

 nish more moisture than does the earth, so that two- 

 thirds of the species are confined to the first two sub- 

 strata on this account. If so, the cause of scarcity, even 

 of earth forms, may, after all, be dry climate. 



LIST OF SPECIES AND VARIETIES. 



1. Ramaliua calicaris (L.) Fr. var. fraxinea Fr. 



On trees, infrequent. July 4, 1896, no. 89. 

 Not previously reported from Minnesota. 



2. Ramaliua calicaris (L. ) Fr. var. fastigiata Fr. 



On trees, frequent. July 4, 1896, no. 89a. 



3. Ramaliua calicaris (L.) Fr. var. farinacea Schaer. 



On Saint Peter sandstone, common. July 11, 1896, no. 170. 

 Not previously reported from Minnesota. 



4. Cetraria eiliaris (Ach. ) Tuck. 



On tamaracks, old fences and Saint Peter sandstone, fre- 

 quent. June 19. 1896, no. 96; July 10, 1896, no. 158. 

 Not previously reported from Minnesota. 



5. Evernia prunastri (L.) Ach. 



On tamaracks, old fences and Saint Peter sandstone, fre- 

 quent. June 19, 1896, no. 19. 



Rare further south, the only other state from which it is re- 

 ported in the Mississippi valley being Iowa, where the writer 

 has collected it twice. 



6. Usnea barbata (L.) Fr. var. florida Fr. 

 On trees, rare. July 4, 1896, no. 92. 



7. Usnea barbata (L. ) Fr. var. hirta Fr. 



On Saint Peter sandstone, rare. July 4, 1896, no. 92a ; July 

 11, 1896, no. 169. 



Passes into the next. 



8. Usnea barbata (L.) Fr. var. rubiginea Michx. 



On Saint Peter sandstone, common. July 11, 1896, no. 169a. 

 Not previously reported from Minnesota. 



9. (Jsnea angulata Ach. 



On tamarack, very rare. June 19. 1896, no. 21. 

 Not previously reported from Minnesota. 



