strenuous conditions. Arenaria grccnlandica with its multitud- 

 inous rootlets and branching habit, Solidago virganrea alpina 

 and Potentilla tridentata, similarly provided, are pioneers upon 

 this very xerophytic habitat. Diapensia lapponica, with its 

 cushion habit, is also a pioneer and reaches here its greatest 

 development, being characteristic of this stage. Salix uva-ursi, 

 Rhododendron lappomcum, Arctostaphylos alpina follow closely 

 upon Diapensia forming almost a definite zone. These forms, 

 on passing back from the brow, soon give rise to a definite mat 

 in which occurs V actinium uliginosum which latter becomes here 

 the character plant of the Alpine Tundra. It is accompanied 

 by Empetrum nigrum, Ledum latifolium, Kalmia glauca, and K. 

 angustifolia. Several grasses and carices, Juncus trifidus and 

 Scirpus ccespitosus now appear and, with several mosses, make 

 the Alpine Tundra complete. It was noticeable that as the 

 mat developed Diapensia gradually disappeared, being entirely 

 absent when it reached its characteristic development. 



(d). The Krummholz. With the formation of a sufficient 

 humus to support higher forms, trees encroach upon the Alpine 

 mat. Betula papyrifera minor and B. glandulosa are the first 

 to make their appearances. They show a high development of 

 the Krummholz habit, lying prostrate upon the mat. Locally 

 Larix americana and Juniperus communis nana are the pioneers, 

 especially is this true upon the spurs. Following these pioneers 

 comes the Picea- Abies combination. Islands of spruce and fir 

 deploy as advance guards of the forest proper (Fig. 2). Which 

 of these two trees is the pioneer, that is the more xerophytic, is 

 problematical. The evidence is contradictory. Three possible 

 theories may be presented: I. Picea is the xerophytic pioneer, 

 followed by Abies as the conditions become more and more 

 mesophytic. The evidence from the Great basin, North basin, 

 and clearing societies would favor this idea. 2. Abies may be 

 the more xerophytic. This idea finds little support except in 

 places where Abies is the dominant species. 3. Neither is to be 

 considered as the pioneer. It is more a question of preoccupa- 

 tion. The first to appear stays and there is no question of suc- 

 cession. This theory seems to explain very satisfactorily all 

 conditions, especially that on the "tableland" and "saddle," where 



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