plants whose demands are higher. To this organic decay 

 must be added the more efficient weathering which so dis- 

 integrates the granite that it often crumbles beneath the feet. 

 Under the action of these two forces a residual soil is soon 

 formed and new plants make their appearance. 



(b). The Reindeer-Iceland Moss Society. In these rock 

 angles and cracks, only a very shallow soil having accumulated, 

 the fructicose lichens now appear. As pure growths they never 

 form mats of large extent for, having no means of secure attach- 

 ment, they are easily dislodged by heavy winds and rains and 

 washed away. So the excessive development of this society as 

 such is retarded. Cladonia rangiferina, C. rangiferina alpestris, 

 and Cetraria isandica may be mentioned as the characteristic 

 components. With them are associated several less prominent 

 forms. Cladonia cristatella may be noted. Several mosses may 

 also attain prominence in this society. Bazzania trilobata is not 

 an uncommon form, frequently forming extensive patches. 



This mat once established becomes a center of accumulation, 

 retaining the detritus of wash and erosion as well as that of local 

 plant decay which is not a little, for these lichens and mosses 

 grow above, dying down behind in a manner not unlike that of 

 Sphagnum. Very soon a sufficient soil exists and still higher 

 ecological forms have their introduction. 



(c). The Alpine Tundra. With the accumulation of soil the 

 food material becomes greater and of a higher nature. The 

 grasses and sedges first appear and, spreading with their inter- 

 lacing roots, soon make the precarious lichen-moss mat a fixity. 

 Hierochloe alpina, Agrostis rubra, Dcschampsia ne.ruosa, Care:: 

 vulgaris hyperborea, C. canescens alpicola, and Juncus trindns 

 are perhaps the most characteristic of these forms, pioneers of 

 the Alpine Tundra. Many less prominent forms are associated. 

 By the coalescence of mats a turf is formed. Some of the lich- 

 ens still persist but have been largly forced out. Many mosses 

 are also common at this stage, probably as pioneers rather than 

 relicts of a former stage. Polytrichnm junipennum and 

 Mielichhoferia nitida elongata form dense isolated patches, while 

 Polytrichum commune and P. Ohioensis are more ubiquitous 

 forms. 



31 



