2&8 SOIL TYPES [chap. 



of strong soils are the primrose {Primula vulgaris), 

 and the wild carrot {Daucus carota). 



Peaty Soils. 



The accumulation of humus to form peaty soils has 

 already been discussed, and is associated with water- 

 logging, which cuts off the access of air and so sets 

 up an anaerobic fermentation of the residues of the 

 vegetation growing upon the surface. There is always 

 a deposit of ferric hydrate accompanying the accumu- 

 lation of peat, as explained before. As the reclama- 

 tion of peaty soils has already been dealt with, it will 

 be sufficient here to indicate that their great character- 

 istic is a deficiency in soluble mineral constituents, 

 notably salts of lime and potash. It has also been 

 mentioned that, as a consequence of the acid nature 

 of the medium, the bacteria of nitrification are absent 

 or few in number. All attempts at the cultivation 

 of peaty soils begin with drainage, and must then 

 proceed on the basis of neutralising the organic acids 

 with lime and providing a sufficiency of mineral food 

 for the plant, thus also inducing nitrification to render 

 available the large quantities of nitrogen which have 

 accumulated. Of the common crop plants, oats and 

 potatoes are perhaps the most tolerant of extreme 

 amounts of acid humus. The normal vegetation of 

 peaty soils is a mixture of xerophytic and calcifuge 

 forms; the Conifers, the Ericaceae, Drosera, Rumex 

 Acetosella, Pedicularis sylvatica, Sphagnum moss, and 

 many sedges and rushes, are characteristic of sour, 

 peaty soils. Other characteristic plants are more pro- 

 perly Northern or Arctic species, and, occurring only in 

 the uncultivated uplands, need not be considered here. 



