THE SOIL IN RELATION TO PLANT GROWTH 145 



covered with a mixed growth of grass and weed, which was grazed by 

 stock and gradually deteriorated as the old drains choked up and the 

 land became more and more waterlogged. Aira ccespitosa, "bent" 

 grass (Agrostis vulgaris), yellow rattle (Rhinanthus Crista-galli), and 

 in dryer places the quaking grass (Briza media} and ox-eyed daisy 

 (Chrysanthemum Leucanthemuiri] are among the more obvious plants on 

 these neglected fields ; the only relics of the past are the field names 

 and the high ridges or " lands " made years ago to facilitate drainage. 

 But recently marked improvement has set in. Drainage is gradually 

 being attended to, whilst additions of lime and phosphates (as basic 

 slag) have markedly improved the herbage, favouring the development 

 of white clover (Trifolium repens) and the pasture grasses, and crowding 

 out the weeds. Potassic fertilisers are not usually needed. Only in 

 the dry eastern counties has the old arable cultivation survived. 



Many of the ecological and agricultural observations on clay need 

 revising in view of the distinction which has recently been set up 

 between the silty clays and the true clays. The former owe their 

 heaviness to the large amount of fine silt present, and as this substance 

 is not nearly as finely divided as clay it does not show the true 

 colloidal properties, and is not flocculated by lime, frost, etc. 

 Indeed no way is known for ameliorating these soils and they are 

 generally left as rather poor pasture. The true clays are often 

 indistinguishable on casual inspection, but they behave differently on 

 cultivation and respond to lime and good treatment whenever it is 

 deemed worth while to improve them. 



Sandy soils are formed of large silica particles deficient in colloidal 

 matter, and therefore possessing little power of cohesion, or of retain- 

 ing water or soluble salts. Hence they tend to be dry, loose, and poor 

 in soluble substances " hungry," the practical man calls them. Their 

 behaviour towards vegetation depends very largely on their position, 

 their depth, and the nature of the subsoil, these being the factors that 

 determine the water supply to the crop. The water supply is usually 

 satisfactory when the surface soil contains sufficient clay and not too 

 much coarse sand and gravel, and rests on a deep subsoil containing 

 rather more of the finer particles. It is a further advantage if other 

 land lies higher and furnishes a supply of underground water. In 

 such cases the land is nearly always cultivated ; it yields early crops 

 of high quality rather than heavy crops, the tendency to drought in- 

 ducing early maturation, while the absence of stickiness makes sowing 

 an easy matter at any time. Fruit, potatoes, and market-garden pro- 

 duce are often raised, and high quality barley is also grown. The 



