VEGETATION OF ROCKS AND WALLS 289 
lensis, or a variety of the alpine form—e.g., Arenaria 
verna var. Gerardi. 
Many lowland plants grow in the more sheltered places, 
even to the summits of the highest mountains. They are 
often dwarfed, and some—e.g., Poa annua and Festuca 
ovina—seldom produce flowers, but multiply vegetatively 
(see p. 160). The following list, compiled largely from 
Williams’s High Alpine Flora of Britain,* shows the 
highest range of the plants, usually in the Scottish 
Highlands : 
Viola palustris, 4,000 feet. Lychnis dioica, 3,500 feet. 
Galium saxatile, 4,000 feet. Tussilago Farfara, 3,500 feet. 
Euphrasia officinalis, 3,980 feet. Oxalis A cetosella, 3,480 feet. 
Rumex Acetosa, 3,980 feet. Viola lutea, 3,450 feet. 
R. Acetosella, 3,980 feet. | Agrostis canina, 3,400 feet (Carran- 
Ranunculus acris, 3,980 feet. | tual, Ireland). 
Achillea Millefolium, 3,980 feet. | Chrysosplenium oppositifolia, 3,400 
Poa annua, 3,980 feet. feet. 
Cardamine flexuosa, 3,900 feet. Heracleum Sphondylium, 3,300 
Taraxacum officinale, 3,900 feet. feet. 
Solidago Virgaurea, 3,900 feet. | Stellaria uliginosa, 3,300 feet. 
Campanula rotundifolia, 3,800 feet. | Potentilla Tormentilla, 3,300 feet. 
Cardamine hirsuta. 3,800 feet. Mercurialis perennis, 3,300 feet. 
Festuca ovina, 3.770 feet. Sagina procumbens, 3,290 feet. 
Thymus Serpyllum, 3,700 feet. Viola Riviniana, 3,000 feet (Car- 
Caltha palustris, 3,600 feet. rantual, Ireland). 
Veronica serpyllifolia, 3,500 feet. | Lotus corniculatus, 2,800 feet. 
Adoxa Moschatellina, 3,500 feet. Anemone nemorosa, 2,750 feet. 
On dry exposed rocks the only vegetation consists of 
close-growing lichens and minute mosses ; there is neither 
sufficient water nor nutriment to support flowering plants. 
On dry rocky summits, too, vegetation is scarce. Lichens 
—e.g., Cetraria islandica and species of Cladonia—and 
the woolly fringe-moss (Rhacomitrium lanuginosum) are 
usually common. The latter occasionally forms a thin layer 
of peat in which a few starved and stunted flowering plants 
become established—e.g., Empetrum, Vaccinium, Lyco- 
podium Selago, Potentilla Sibbaldi. Gnaphalium supinum, 
Azalea procumbens, Salix herbacea, Juncus trifidus, Carex 
rigida, Festuca ovina. All except the last three are low- 
lying plants, which form a mat close to the ground, and 
so escape the full force of the wind. 
* In Annals of Scottish Natural History, 1908-1910. 
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