24 SOILS AND MANURES. [CHAP. n. 



not necessary to all plants : but all the earths I 

 have enumerated have been found in the ashes 

 o{ the cabbage, the parsnep, and other common 

 garden vegetables. It is, therefore, not sur- 

 prising that the most productive soils are those 

 which contain the greatest variety of sub- 

 stances. Of all the primitive earths found in 

 garden vegetables, lime is the most abundant, 

 and hence one of the best soils for gardening 

 purposes is generally allowed to be a calcareous 

 loam on a chalky subsoil: as this sort of soil 

 is composed of nearly equal parts of lime, sand, 

 and clay, enriched by depositions of decayed 

 animal and vegetable matters. The next best 

 soil is a sanely loam, composed of clay and 

 sand, also mixed with decayed animal and 

 vegetable matters ; and the worst soils are 

 loose sand, moist black peat, and stiff clay. 

 The first of these soils can only be rendered 

 fertile by the addition of clay ; and the peat 

 and clay are improved by the help of lime or 

 sand. "A gravelly or sandy subsoil is generally 

 better than a clayey one : but in dry seasons 

 the plants are soon burnt up, while those on a 

 clayey subsoil remain fresh and green. A poor 

 sandy soil is necessarily a barren one, as, from 

 the looseness of its particles, it will not retain 

 moisture enough round the spongioles of the 

 roots to keep them in a healthy state ; and a 

 stiff clay is unfertile, from the closeness of its 

 texture not admitting air to the roots, which 

 also waste their strength in the efforts they 

 make to penetrate its adhesive clods. 



Manures. — W hen the soil in which plants 

 are to be cultivated is deficient in any of the 



