x.] CALCAREOUS SOILS 327 



beam tree {Pyrus aria), dogwood (Cornus sanguined), 

 and Clematis vitalba, among shrubs. 



The vegetation is characteristically rich in flower- 

 ing plants : amongst the Leguminosae, the horse-shoe 

 vetch {Hippocrepis comosa), bird's-foot trefoil {Lotus 

 corniculatus), kidney vetch {Anthyllis Vulneraria) are 

 everywhere abundant ; milkwort {Poly gala), bladder 

 campion {Sileue inflatd), Spircea filipendula, burnet 

 {Poterium sanguisorbd), wild parsnip {Pastinaca sativa), 

 sheep's scabious {Scabiosa columbaria), chicory {Cicho- 

 rium intybus), and certain of the Gentianaceae, as G. 

 amarella and Chlora perfoliata, the viper's bugloss 

 {Echium vulgare), and a number of labiates like Ori- 

 ganum, are characteristic of the pastures and waste 

 places on chalk and limestone. Amongst grasses, 

 Avena pubescens, A. Jlavescens, Bromus erectus, and 

 Brachypodium pinnatum are common. 



t While it has been indicated that many plants are 

 intolerant of lime, others show the effect of any excess 

 in the soils by a stunted development of the plant, 

 often accompanied by a reduced size of the leaf, and 

 a sickly yellow or even white colour. This unhealthy 

 condition of "chlorosis" is particularly noticeable on 

 the stiff marls, which are but little aerated but contain 

 much calcium carbonate; on the Continent it often 

 affects vines, particularly when grafted on American 



stocks. 



Clay Soils. 



It has already been indicated that clay soils are 

 those in which the finer fractions of sand, silt, and 

 clay predominate ; the presence of any considerable pro- 

 portion of coarse sand causes the soil to become friable, 

 and would class it with the loams. The texture of 

 clay soils naturally varies very much ; the heaviest 

 clays occur in dry climates, where the percolation 



