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 procumbens, Saxifraga tridactylites, Poa annua, 
Asplenium Ruta-muraria, and Cardamine hirsuta, and on 
old walls where more soil has collected, Parietaria offici- 
nalis, Linaria Cymbalaria, Lactuca muralis, Diplotaxis 
muralis, Epilobium lanceolatum, etc. On the wall-top 
mosses are abundant, and growing amongst them many 
annuals and a few perennials characteristic of dry soils— 
e.g., Capsella Bursa-pastoris, Cerastium vulgatum, C. 
semidecandrum, Erodium cicutarium, Valerianella olitoria, 
Filago germanica, Myosotis collina, Veronica agrestis, V. 
arvensis, V. serpyllifolia, Thymus Serpyllum, Antirrhinum 
majus, Cheiranthus cheiri, Arenaria serpyllifolia, Medicago 
lupulina, Sempervivum tectorum, Hieracium Pilosella, 
Rumex Acetosella, Centranthus ruber, many small grasses, 
and very frequently Polypodium vulgare. 
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 commonly 
met with: Jasione montana, Cotyledon Umbilicus, Lepi- 
dium Smithii, Geranium molle, G. lucidum, Sedum species, 
Erica cinerea, Calluna vulgaris, Genista pilosa, and many 
ferns, including Adiantum Capillus-Veneris, Asplenium 
lanceolatum, A. Adiantum-nigrum, A. Trichomanes, Cete- 
rach officinarum, ete. 
