CHAPTER XXIX. 

 ON HABVESTING SOILS AND COMPOSTS. 



1629. Plants derive the chief part of their food from the soil, and as 

 the growth of different species of plants is promoted by certain substances 

 taken up in different proportions from it, which requires to be replaced in 

 order to reproduce the same crop, it is obvious that this renovation of the 

 soil is a very important part of gardening, as it is of cultivation on a greater 

 scale. Much discrimination and judgment is therefore required in the pre- 

 paration of composts and arrangement of the manure-heap. A rough analysis 

 of natural soils usually presents a per-centage of silica, oxide of iron, alumina, 

 potash, and other substances, which enter into their composition with certain 

 organic matters, to which they owe much of their fertility. The organic matter 

 is of a very complex character, and owes its origin in a great degree to vegetable 

 remains, as the roots and stems of former crops ; but also, in part, to decayed 

 animal remains, both of which are found to decompose under the influence of 

 water, air, and heat, producing a blackish-brown powdery substance- on ana- 

 lysis, known as h2inuis, — a substance which includes a great many vegetable 

 acids in its composition. 



1630. " The opinion of chemists is much divided," Dr. Scoficrn remarks, in 

 his recently-published work on the "Chemistry of Soils,"* "as to whether 

 the hujnic acid bodies, when dissolved, are actually absorbed by plants, as 



• Handy Book of the Chemistry of Soils. By J. Scoffern, M.B. Bell & Daldy. 



