i9o8] COOPER— ALPINE VEGETATION IN COLORADO 325 



have been split off blocks of very large size, no plants except lichens 

 have as yet been able to gain a foothold. Wiere the blocks are 

 smaller and more disintegrated, a layer of fine material has accumu- 

 lated around and among them— the first step in the formation of a 

 soil; and here a few herbaceous plants of extreme xerophytic nature, 

 such as Silene acaulis, Phlox caespitosa, Dryas odopetala, have 

 established themselves. A further stage is seen where the vegetation 

 has become more -luxuriant both in number of species and of individu- 

 als, frequently partially concealing the remnants of the disintegrating 

 rock fragments. In the mature dry meadow the rock fragments have 

 mostly broken down to form, with the humus deposit, an even layer 

 of soil which is well covered by a growth of low herbaceous vegetation. 

 The dry meadow of this region resembles quite closely the so-called 

 "alpine tundra" of the summit of Mt. Ktaadn, Maine, as described 

 by Harvey,' and observed by the author of this paper. It differs 

 from that in the practical absence of mosses and fruticose lichens so 

 <:haracteristic of the summit of Ktaadn. At the same time, it does 

 not perfectly correspond with the common idea of meadow land, 

 since the vegetation is low and of a decidedly xerophytic nature. As 

 is the case in the Pike's Peak region^ the mature dry meadow has two 

 seasonal stages, the earlier characterized by the prominence of 

 Rydhergia grandiflora in flower, the later by Campanula rotundijolia. 

 It must not be supposed that the soil on these exposed summits and 

 slopes, thin as it is, is everpvhere dry. Even along the summit of the 

 divide are frequent depressions receiving all the run-off from the 

 •surrounding slopes, which often are gentle and embrace large areas. 

 The soUd granite beneath prevents absorption; therefore the water 

 remains stagnant or flows very slowly over the surface. The supp y 

 seems to be fully equal to the loss by evaporation, for these areas 

 remain wet all summer long. The depressions are characterized b> 

 a more luxuriant vegetation, and therefore deeper deposits of humus 

 but the species are the same as those found on the drier portions ot 

 the meadow. A Ust of the dominant species of the dry meadow 

 follows : 



T f Aff TTtaadn Elaine. 



^ IL\RVEY, LeRov H., a study of tbe physiographic ecoIog>- ot mu r. 



TJniver5ity of Maine studies, No. 5. 



3 Clemekts, F. E., Research methods in ecolog}% 



