138 Plant-formation of Siliceous Soils 



Quercus sessiliflora are strikingly pure; in others the pedun- 

 culate oak (Q. Rohur) is more or less mixed with the 

 sessile-fruited species, but whether this is always due to 

 planting, as is apparently the case in the Pennine woods, 

 or whether it is sometimes a natural mixture, as it cer- 

 tainly is in many of the oakwoods of sandy soils previously 

 described (p. 92), is not yet clear. 



The associated trees and shrubs in these various woods 

 are, for the most part, and so far as they have been 

 studied, much the same as on the Pennines, but some 

 interesting variations occur. Thus on some of the Lake 



District hills which receive a very heavy 

 T„QQ^g rainfall the oakwoods contain a great deal 



of ash, which is by no means confined to 

 streamsides as on the Pennines, but spreads through the 

 woods in all directions, largely replacing the oak, which 

 has probably been extensively removed. The ground 

 vegetation, however, is that of a typical oak wood of 

 siliceous soil. Some of the Devonshire woods of Quercus 

 sessiliflora also contain much generally distributed ash. 

 The ground vegetation of most of these woods closely 



corresponds with the three tjrpes recognised 

 Bryophyte -ij^ ^j^g Pennine woods or with transitions 

 vegetation between them, but, as in the case of the 



associated trees, variations occur. 

 Thus in the oakwoods of Co. Wicklow at Grlendalough 

 the ground vegetation is largely dominated by mosses, 

 species of Dicranum, Hyprmm and Polytrichum, with 

 local patches of S'phagnum and also many Liverworts; 

 a similar type of ground vegetation occurs in the 

 woods of Q. sessiliflora on the sides of the valleys near 

 Aberystwyth in Central Wales. 



The woods of Quercus sessiliflora at Killarney in Co. 



Kerry, south-west Ireland, are specially 

 woods *^ interesting as being the chief station in the 



British Isles of the strawberry tree {Arbutus 



