272 BRITISH PLANTS 



C. Woods on Calcareous Soils 



(e.g., chalk, limestone, marls, and other soils rich in lime). 



I. Ash-Oakwood Association. On deep calcareous 

 clay a wood intermediate between the damp oak-wood 

 and the ash-wood is found in many parts. The oak and 

 ash share dominance and the ground- vegetation is very 

 similar to the damp oak-wood, but the wayfaring-tree, 

 spindle-tree, and clematis are common here, yet rare in 

 the oak-wood. The dogwood, privet, maple, sloe, and 

 hawthorn also are far more abundant in this type of wood. 

 Of the herbaceous undergrowth, the following are char- 

 acteristic : Paris quadrifolia, Colchicum autumnale, Iris 

 foetidissima, Epipactis media, E. purpurata, and Cam- 

 panula Trachelium. 



II. Ash-Woods. These are the typical woods on lime- 

 stone, where the soil is dry and poor in humus. The ash 

 does not cast much shade, and the undergrowth is conse- 

 quently rich and varied. The most frequent trees other 

 than ash are the wych-elm (Ulmus montana) and haw- 

 thorn. Many lime-loving species are present -e.g., white 

 beam (Pyrus Aria), wayfaring-tree, yew, Inula Conyza. 

 Scabiosa Columbaria, Carduus eriophorus (woolly-headed 

 thistle), Origanum vulgare, etc. Heath-plants are absent, 

 except where the limestone is covered with glacial clay 

 or marl from which the lime has been washed out. 



This type of wood gradually merges into the ash- 

 oakwood at low altitudes, as the soil becomes damper, 

 and at high altitudes birches replace the ash. 



III. Beech-Woods. The beech- wood is confined almost 

 entirely to the chalk of South-East England, where it 

 occurs as a zone on the borders of the damp oak-wood 

 which covers the clay-with-flints on the top of the Downs. 

 It also occurs to the west of England on the oolitic lime- 

 stone of the Cotswold Hills. The branches of the beech 

 are placed horizontally, and the leaves being situated in one 

 plane, cast a very deep shade, which prevents the develop- 

 ment of all undergrowth except a few mosses e.g., Leuco- 

 bryum. Every autumn the ground receives an enormous 

 harvest of falling leaves, and as these decay slowly they 

 form another unfavourable factor for the production of 

 ground- vegetation. The trees and shrubs present in the 



