46 GARDEN maxage:jext. 



dei'ed it as remarkable for its fertility as it had been before for the reverse. 

 The authorities, however, are not agreed as to the causes of this increased fer- 

 tihty. In the natural state of clay, it may be digested for hours with concen- 

 trated sulphuric acid without dissolving ; but, when slightly burnt, it dissolves 

 in acids with great ease, while the sihca is separated into its gelatinous and 

 soluble form. The soil is rendered accessible to air, oxygen, and carbonic 

 acid, according to Liebig ; and these are the principal conditions favoxirable to 

 the development of roots. Common potter's clay contains within it all the 

 constituents necessary to the luxuriant growth of plants ; but they must be 

 presented in a state fit to be taken up by the roots of plants— gentle calcina- 

 tion communicates these properties. 



lao. Burning the soil thus operates by chemical and mechanical agency ; 

 the compact clay has been hitherto impervious to atmospheric influence ; the 

 half-decomposed remains of former crops have remained in the soil an inert 

 mass of organic matter. By burning, the saline constituents of former ci-ops 

 are unlocked and rendered soluble in water, and become available as food to 

 the plants. ]\Ioreover, the application of heat has rendered the surface 

 porous and friable,— its mechanical condition has undergone an entire change ; 

 and Liebig considers that its power of attracting ammonia from the atmo- 

 sphere is increased far bej-ond that of any natural soil ; while Dr. Voelcker 

 regards potash, which is liberated on burning the clay, as the chief source of 

 its eflScac}'. 



121. Burning is attended with especial advantage to peat soils, in which the 

 accumulation of organic matter is prejudicial to all vegetation. In burning, 

 the sour humus which is formed by marshy soils is destroyed, and the insoluble 

 particles occurring in it rendered soluble and available as fertilizers. 



122. Next in importance to these operations is the application of lime and 

 atmospheric air, which is a combination of oxygen and hydrogen ;— one of 

 the objects of drainage being to admit oxygen, with the other constituents 

 of atmospheric air, into the soil. This process is facilitated by the deep 

 trenching which usually follows the thorough drainage of a garden ground. 

 The immediate object of trenching is to deepen the soil, and prepare the sub- 

 soil to nourish the fibres of deep-rooting plants. The operation is commenced 

 by throwing out the top spit to a convenient breadth for the workman, and 

 wheeling it to the farther end of the bed or quarter ; the second spit is treated 

 in the same manner if the trenching is to be three spades deep. This done, 

 the bottom of the trench is dug up as roughly as possible so that it is left level. 

 The top spit of a second portion of the ground is now removed and placed 

 alongside the fu-st, and the second spit of this portion is dug up and placed 

 roughly over the first trench. The fii-st spit of a third portion is now removed 

 and placed in as large masses as possible over the first trench : the bottom of 

 the second trench is now dug up in the same manner as the first, and so on till 

 the whole is finished. Thus, while the entire soil is stu-red to the depth of 

 two feet, it retains its original position ; the smface being left exposed for 

 a time in rough vmbroken lumps, till it crumbles naturally under the dis- 



