Hedgerows and Hedgebanks 59 



Hedgerows and Hedgebanks. The use of some sort of barrier, whether 

 wall, hedge, or ditch, delimiting property, as land isolated for some special 

 purpose, or for preventing cattle from straying, would appear to be a natural 

 commonplace of human occupation. Walls and hedges may play a subsid- 

 iary part in a local flora, the more conspicuous as the plants are usually 

 elevated to a position in which they attract the eye ; and these formations 

 afford a wide range of secondary biological stations of particular interest. 



(1) The masonry wall of squared cut stone (ashlar), or of rough 

 rag-stone from the Limestones of local Corallian or Portland beds, soon 

 affords a nidus for intrusive rock-plants, germinating in cracks of the 

 stonework, following mosses and lichens which obtain water from the damp 

 stone, the more conserved internally as the outer surface may be impervious, 

 and channels follow the lines of rain-drip. Walls built of the eminently 

 soft, porous, and rapidly weathered free-stone from the older Headington 

 quarries, soon develop a flora of a few grasses and larger flowering plants, 

 of which the most conspicuous are 



Senecio squalidus? (Dianthus caesius)? 



Hieracium murale, 2 Snapdragon and Wallflower. 



Only very exceptionally in this district do old stone-walls carry small 

 ferns : 



Polypodium vulgare, Cetarach officinarum, 



Asplenium Ruta-muraria, Asplenium Adiantum-nigrum. 



(2) Rough rag-stone walls of farmsteads, gardens, etc., with or^without 

 mortar, acquire a moss-layer, soon giving a coating of fine soil, which may 

 carry a miniature crop of Draba verna in early spring, followed by a special 

 flora of diminutive forms (Iffley, Hinksey, Horspath, Headington) ; cf. : 



Senecio vulgaris, one inch high, reduced to one terminal capitulum. 



Valeriana olitoria, -| inch. 



Arenaria serpyllifolia, 10 mm. high, reduced to one terminal flower: also 



Linaria Cymbalaria, Poa annua, 



Crepis taraxacifolia, Sderochloa rigida. 



These tend to wholly disappear as summer heat shrivels them ; and only 

 specialized xerophytes retain their stations : 



Sedum acre, Saxifraga tridactylites^ 



Sedum reflexum, 



Sedum dasyphyUum^ 

 with starved forms of grasses as 



Festuca bromoides^ Hordeum murinum, 



Poa compressa, Bromus sterilis ; 



and more casually, Corydalis lutea, Linaria purpurea^ Centranthus ruber, 

 Verbascum Thapsus, with more definitely alien Cheiranthus, Antirrhinum, 

 and obvious garden-escapes as Arabis alpina, Arenaria, Alyssum, and 

 planted Sempermvum tectorum. 



(3) The case of the rough stone wall grades naturally into that of the 

 hedgebank built more or less of a mixture of stones and earth, as a station 

 with considerable possibilities from light-exposure ; but subject to reduced 

 water-supply as the summer advances, ultimately becoming wholly dry 

 from above. On such hedges the spring vegetation may be abundant ; 

 but later in the season they show little more than the usual associates 

 of waste-places and rubbish heaps, with no special characteristics of 

 their own. 



1 Hence commonly known as the ' Oxford Groundsel ', the bright yellow flowers of which have 

 been seen on the Examination Schools (erected 1882), on the Radcliffe Camera and many old 

 buildings and College walls : on the Town Hall (built 1897) immediately following clumps of moss. 



2 On old walls, Lincoln College, Blue Boar Lane, often very conspicuous. 



* Residual on wall of Wadham College, and St. Hilda's (once Sibthorp's residence). 



