60 ILLINOIS STATE ACADEMY OF SCIENCE 



The descriptions of these formations given below are 

 very brief and no species except type species are named. 

 More detail concerning these will be given in a paper 

 that is to be published. 



On the rock uplands, the lichens are pioneers as they 

 are elsewhere, but they are of shorter duration except on 

 the perpendicular surfaces, for crevices and slopes are 

 soon taken up with shrubs such as Diapensia lapponica, 

 Salix uva-ursa ( ?), and Dryas octopetala ; and these form 

 the thin scattered cushions of vegetation called "fell 

 fields" above. Their growth continues until they cover 

 the ground with a thick carpet in which other plants in- 

 termingle. Potentilla uniilora, P. biflora are prominent 

 in this situation, as are also Arctostaphylos alpina, An- 

 dromeda polifolia, Cassiope tetragona, Rhododendron 

 lapponica. One or another of these may be dominant in 

 any particular location, depending perhaps on priority 

 of occupancy; and hence arise the names of Dryas 

 tundra, etc., used by Warming. These shrubs may be- 

 come so thickly intergrown in later stages with sedges 

 and grasses and herbaceous plants that the shrubby 

 character may be lost entirely, and in this situation the 

 Potentilla and bearberry, perhaps, are the best survivals 

 of the shrubs. This stage is regarded by the writer as 

 a probable transition stage between the dwarf shrub and 

 the Sphagnum-Ericad tundra mentioned below. The 

 rapidity with which dwarf shrubs cover the ground and 

 develop the thick carpet just described depends upon the 

 protection from wind, as stated before. The windward 

 and lee slopes of a hill offer strong contrasts to each 

 other, and even on one boulder, the protected and exposed 

 sides may show, in one case, a solid covering, and in the 

 second, a perfectly bare surface except for a few lichens. 



Succeeding the more open stages of the dwarf shrub 

 associations there may be the cotton grass-sedge asso- 

 ciation, developed in situations made hydrophytic by 

 configuration of the land and drainage influenced thus. 

 These places show accumulations of rock soil and reveal 

 on digging the frozen condition of this soil. Dryas may 

 remain with the sedges, but it is infrequent, and the other 

 shrubs are even still rarer, but mosses and herbaceous 



