ENGLISH AGRICULTURE. 25 



without it; but all fertile soils contain the remains of the 

 roots, stems, and leaves of former generations of plants, and, 

 in the case of agricultural land, farmyard dung and other 

 organic substances added to the soil. Without vegetable 

 matter most soils would be unfertile. Vegetable matter 

 gives a consistency to soils most welcome to plants, and 

 confers physical properties upon them which renders them 

 a safe and good anchorage and home for the spreading roots. 

 It regulates the conditions of the soil with reference to both 

 heat and moisture, keeping it cool, for it very quickly radiates 

 heat, but likewise keeping it moist, because it retains moisture 

 with great persistency. One of the chief advantages of 

 repeated dressings of farmyard dung is that the hygroscopic 

 properties of the soil are greatly improved. It enables the 

 soil to retain moisture, it keeps it cool, and it gives it a 

 peculiar texture suitable for the ramification or free passage 

 of the roots of growing plants. These are the mechanical 

 functions of organic matter. 



But it has other important uses. Organic matter is the 

 chief source of nitrogen in soils. The vexed subject as to the 

 sources of nitrogen must be looked upon as under controversy. 

 I have no doubt that plants obtain a certain amount of 

 itrogen from the air. Probably in the long run soil has 

 received it all from the air ; but in a cultivated soil, where 

 nitrogen exists in organic matter, no doubt the plants take 



largely from the soil. There is, indeed, full proof that 

 nitrogen is taken largely from the soil ; and as the organic 

 matter in soils contains large quantities of nitrogen, it is a 

 principal source of this most important element of fertility. 

 By its constant decay, organic matter becomes a source of 

 carbonic acid gas; and as the rain falls upon a soil im- 

 pregnated with organic matter, it absorbs carbonic acid gas, 

 and its solvent action upon mineral matters is thereby much 

 increased. 





