VEGETATION OF ROCKS AND WALLS 291 



the way for the germination of the seeds of flowering 

 plants. The most common of these are Sedum acre, 

 Sagina procumhens, Saxifraga tridactylites, Poa annua, 

 Asplenium Buta-muraria, and Cardamine hirsida, and on 

 old walls where more soil has collected, Parietaria offici- 

 nalis, Linaria Gymbalaria, Lactv^a muralis, Diplotazis 

 muralis, Epilobium lanceolatum, etc. On the wall-top 

 mosses are abundant, and growing amongst them many 

 armuals and a few perennials characteristic of dry soils — 

 e.g., Capsella Bursa-pastoris, Cerastium vulgafum, G. 

 semidecandrum, Erodium cicutarium, Valerianella olitoria, 

 Filago germanica, Myosotis collina, Veronica agrestis, V. 

 arvensis, V. serpyllifolia, Thyrmos Serpyllum, Antirrhinum 

 majv^, Cheiranthus cheiri, Arenaria serpyllifolia, Medicago 

 lupulina, Sempervivum tectorum, Hieracium Pilosella, 

 Bumex Acetosdla, Centranthus ruber, many small grasses, 

 and very frequently Poly podium vulgar e. 



The walls which bear the richest flora, however, are 

 those built up of rough blocks of stones held together 

 with mud. These are frequently built in rocky upland 

 districts to separate fields, and represent the hedgerow of 

 the lowlands. These walls become the home of many 

 plants from the surrounding fields, and in addition to 

 those in the preceding list the following are commonlj' 

 met with : Jasione montana, Cotyledon Umbilicus, Lepi- 

 dium Smithii, Geranium molle, G. lucidum, Sedum species, 

 Erica cinerea, Galluna vulgaris. Genista pilosa, and many 

 ferns, including Adiantum Capillus- Veneris, Asplenium 

 laneeolatum, A. Adiantum-nigrum, A. Trichomanes, Gete- 

 rach officinarum, etc. 



