260 BRITISH PLANTS 



(see p. 89), and so we find the vegetation of limestone 

 and chalk hills is made up of a mixture of these two types. 

 The herbage on the windward side of the hill is short, the 

 plants seldom rising more than an inch or two above the 

 ground, but in the sheltered parts the plants grow more 

 luxuriantly, and it is here that most of the calciphilous 

 plants mentioned below are found. 



The dominant grasses are Festuca ovina, Sesleria 

 ccerulea (in northern counties), Koderia cristata, and Poa 

 pratensis ; common or frequent grasses are Agrostis 

 vulgaris, Cynosurus cristatus (crested dog's-tail), Brachy- 

 podium pinnatum, and Briza media (quaking-grass). Aira 

 flexuosa and Nardus stricta, so common on all other dry 

 soils, are never found where lime is present — that is, they 

 are typical calcifuges (see p. 89). The herbs found on 

 the limestone-pasture and chalk- down include most of 

 those occurring- in the pasture on rich soil (p. 258). Other 

 plants, associated with a dry soil, commonly found are : 

 Potentilla Anserina (silver- weed), Veronica officinalis 

 (common speedwell), Euphrasia officinalis, Carduus acaulis 

 (stemless thistle), and Daucus Carota (carrot). The calci- 

 philous plants may be grouped according to their demand 

 for lime as follows (those marked with an asterisk are 

 more or less rare plants found only on chalk-downs in this 

 country, although on the Continent, where they are more 

 abundant, they i^iay occur on other soils as well) : 



1. Confined to calcareous soil : 



Hippocrepis comosa (horse-shoe vetch), Aceras anthro- 

 pophora (green man-orchid), and Polygala calcarea (chalk- 

 milkwort, found only on the chalk-downs of South 

 England). 



2. Almost exclusively found on calcareous soil : 

 Anthyllis Vulneraria (lady's-fingers), Ophrys muscifera 



(fly-orchid, gr,owing usually at the top of downs under the 

 shade of bushes). Campanula glomerata (clustered bell- 

 flower), and Buxus sempervirens (box-tree). 



3. Prefer calcareous soil : 



* Anemone Pulsatilla (pasque-flower), fi'efo'aw^AewMm Cha- 

 mcecistus (rock-rose), Polygala vulgaris (milkwort), Linum 

 catharticum (purging flax), L. usitatissimum (common flax, 

 linseed), L. perenne (perennial flax), Poterium Sanguisorha 

 (lesser burnet), Viola hirta (hairy dog-violet), Asperula 

 cynanchica (squinancy-wort), Centaurea Calciirapa (star- 



