220 MINNESOTA BOTANICAL STUDIES. 



passing beauty. Hardly less remarkable is the growth of Cla- 

 donia rangiferina (L.) Hoffm. in open woods near Mt. Josephine, 

 single clusters measuring three or four feet across and reaching 

 a foot in height. This plant was also common on rocks and in 

 crevices exposed to wind and sun, but was always much smaller 

 in such locations. It is evidently not a natural pioneer among 

 lichens, but grows after other plants have attacked the rocky 

 substratum, or on a thin layer of soil in crevices, and best of all 

 after trees or shrubs have grown sufficiently to protect it some- 

 what from wind and sun and have not yet become large enough 

 or thick enough to kill it out. This same kind of ecological 

 relation favors Cladonia /areata (Huds.) Fr., a variety of which 

 was found fruiting only in such environment. More is given 

 below about other Cladonias, and the observation could be 

 extended to Stereocaulon. 



After fires have passed over a region destroying the trees and 

 small scattered second growth begins to appear to furnish some 

 protection, Cladonia cristatella Tuck, and a large variety of 

 forms of C. gracilis (L.) Nyl. soon begin to grow in great pro- 

 fusion on old stumps, prostrate logs and bits of decaying wood 

 lying upon, or more or less sunken into the soil. Only a few of 

 the many varieties of the latter plant allowed by European 

 lichenists are recognized in the list of species though forms 

 closely resembling other varieties, so called, are represented in 

 my collections. Nothing seems to be gained by carrying the 

 " splitting" process to extremes without a study of life histor- 

 ies. C. gracilis (L.) Nyl. in regions recently burned showed 

 much less variation than in places where the species had been 

 established longer since the burning, and a careful study of a 

 large number of individuals in this region, extending over a ser- 

 ies of years would enable one to trace the growth and variation 

 within single individuals and thus establish varieties with cer- 

 tainty. Great variety was observed in the plants in regions 

 that had burned 15 or at most 20 years ago so that a study ex- 

 tending over 10 years should be sufficient to give the desired 

 data. 



Like Cladonia rangiferina (L.) Hoffm., C. cristatellaTxxck. 

 is extremely sensitive to environment. In regions where the 

 plants are exposed to sun and wind and in stations of high ele- 

 vation, the plants are much smaller than in better shaded and 

 less elevated places. The relation of size to amount of protec- 



