JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



The difference in properties and values between these three are 

 so familiar to horticulturists that I need not recapitulate them. 

 They arose in past geological ages : the processes involved are no 

 doubt still operative, but they work so slowly that they produce no 

 appreciable effect in our time. 



The second great class of soil constituents, the organic matter, 

 comes in as the result of vegetation. Although not great in amount, 

 it introduces a fundamentally new property : it contains energy 

 stored up from sunlight by the growing plant, is easily oxidizable, 

 and in oxidizing it liberates this energy. Now life is impossible 

 without sources of energy ; the organic matter thus enables life to 

 exist in the soil. Soil contains a great population varying enormously 

 in properties, but all in the last instance dependent on the vegetable 

 residues. It is this that constitutes the great difference between 

 surface and subsoil. 



Organic matter is not strictly essential to plant growth. Plants 

 can be grown in pure sand or even in water, provided the necessary 

 food materials are added. But the process is so tedious that it would 

 be all but impossible on the large scale. Work is lightened enormously 

 by the presence of the organic matter and the accompanying soil 

 population. Three great effects are produced. One of the least 

 obtrusive but most important is the removal of the dead remains of 

 vegetation. The great importance of this function is seen on some 

 of the Rothamsted grass plots, where sulphate of ammonia is applied 

 in large quantities without any lime, so that the soil has become acid 

 and many of the soil organisms are killed. When in late autumn the 

 withered leaves and stems fall back on the soil they simply lie there 

 partially decomposed. After a time they form a dense mat which 

 covers the soil to a depth of two or three inches : this soon becomes 

 so compact and thick that plants cannot force a way through. Only 

 a very few kinds of seeds can germinate on this mat, and before long 

 the plot contains many bare patches and a very limited flora. Clovers 

 and the Leguminosae are completely killed, so also are the weeds : 

 the last survivors are a few grasses, viz. False Oat Grass, Meadow 

 Foxtail, and Yorkshire Fog. 



Wherever the land lies high, or for any reason is left undisturbed, 

 there is always the possibility that a layer of undecomposed vegetable 

 matter may form. On the road between Stafford and Uttoxeter 

 there is a tract of land now covered with 9 inches of peat. The old 

 surface is a red marl so heavily mixed with glacial gravel and pebbles 

 that it could never be cultivated, and therefore was not drained. In 

 consequence organic matter ceased to decompose quickly : a layer of 

 peat was formed which is now nine inches thick, and now the 

 vegetation is mainly sheep's fescue, Nardus, Molinia, and Bilberry. 

 In Yorkshire on the mountain limestone there are similar deposits 

 which form long ribbon-like strips when ploughed, and are difficult 

 to bring under the ground. 



This is the result of having insufficient soil population to demolish 

 the herbage as it falls back. In garden practice another effect would 



