382 BOTANICAL GAZETTE [NOVEMBER 
mune forms patches, especially about old stumps (Polytrichum 
Assoctation) . 
The raised cushions of soil found here are covered by various 
mosses, or by Dendrium buxifolium3? (Dendrium Association). 
In or along the dry stony wash-ways, one finds Saxifraga leucan- 
themifolia, Potentilla tridentata, and Houstonia purpurea. 
The immediate summit of Roan Mountain is characterized by 
the presence of Geum radiatum, Lycopodium selago (Lycofo- 
dium-Geum Association), Menziesia pilosa, Houstonia purpurea, 
Lycopodium lucidulum, Ribes rotundifolium, Dendrium  buxi- 
folium. Alnus alnobetula clings to the north slopes, here form- 
ing a pure growth on the steeper inclines (Alnus Association), 
with Sorbus americana below it, but associated with Rhododendron 
catawbiense on the upper slopes of the dome. 
Crossing Carvers Gap, where Aesculus octandra grows (Aescu- 
lus Association), a rocky outcrop is found on the slope of Little 
Roan Mountain where the writer collected Rhododendron lutea, 
Kneiffia fruticosa, Geum geniculatum, Arisaema quinatum and 
Hypericum graveolens (Kneiffia-Hypericum Association). Alder 
Bald or Elkhorn, as it is called, is reached from Little Roan 
Mountain by crossing a smaller wind gap. The slopes of this 
knob are covered by acres of Alnus alnobetula (A/nus Asso- 
ciation), while the stony places are favorable for the growth 
of Heuchera villosa, Krigia montana, Cerastium vulgatum, and 
two alpine species, Potentilla tridentata and Alsine groenlandica. 
The latter herb assumes the cespitose character in exposed 
situations. 
In conclusion, it is advisable to state that the dwarfing of the 
trees and their absence on the “‘balds” is explicable by the action 
of winter storms which beat upon these summits. Wherever 
the topography is such as to permit the full force of the ice storm, 
there tree vegetation is scanty or altogether wanting, and its 
place is taken by grassy stretches, or by thickets of alder and 
rhododendron, plants which are adapted to withstand ice storms.3® 
37 Cf. SMALL, J. K., Flora of western North Carolina and contiguous territory. 
Mem. Torr. Bot. Club 3. 
3% HARSHBERGER, J. W., Thermotropic movements in the leaves of Rhododendron 
maximum L. Proc. Acad. Nat. Sci. Philadelphia 1899: 219. 
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