﻿1 903] CLADONIA FORMA TIONS 1 9 7 



examine a large number of tali. Consequently, three tali bear- 

 ing quite different Cladonia-formations, growing under different 

 ecologic conditions, were selected for special study. 



The first lichen society to be considered in this paper may 

 be designated as a Cladonia gracilis formation of shaded talus, 

 and the second and third may be appropriately called Cladonia 

 rangiferina formations of shaded talus. The two types are quite 

 dissimilar, as in the first one finds Cladonia gracilis and other 

 smaller Cladonias prevailing to such an extent as to be the only 

 small plants to attract the notice of a casual observer; while in 

 societies of the second type Cladonia rangiferina and other large 

 closely related Cladonias are, at least- on certain small and 

 apparently rather young tali, even more predominant. In some 

 localities, as on the north side of Carlton Peak, may be found 

 tali bearing Cladonia-formations containing both the large and 

 the small Cladonias in about equal proportions. The causes of 

 the differences in composition of these Cladonia-formations 

 are not always easy to trace. Under like conditions as to sub- 

 strata there may be a succession, the larger Cladonias following 

 the smaller, but quite as often species of Cladonia seem to 

 follow the crustose or the foliose lichens, some species of which 

 disintegrate the rocks sufficiently to form a beginning of humus 

 on which the Cladonias may become established. In instances 

 of this kind the Cladonias that gain a foothold may be the 

 larger or the smaller species according to surrounding ecologic 

 conditions. If the lichen society is surrounded with large trees, 

 containing a good number of conifers, and especially pines, 

 the large Cladonia rangiferina and closely related species will 

 predominate. If the trees surrounding or growing upon the 

 talus are small, and especially If devoid of conifers, the smaller 

 Cladonia gracilis and other small Cladonias will prevail. If 

 trees are growing upon the talus, of course they are younger 

 an the talus on which they grow, and relative age of such tali 

 may be estimated somewhat accurately by the size of the trees 

 growing upon them. The talus on Hat Point at Grand Portage, 

 to be mentioned again, estimated thus is the oldest one, and the 

 one at Howenstine Bluff {fg. /), to be considered later, is the 



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