IS PLANTING. 



larger proportion to the saline matters. It contains the elements of which 

 the substance of a tree is composed, viz., carbon, oxygen, hydrogen, and 

 azote. The extract, however, obtained from soils is never perfectly pure, 

 but is always more or less (in all our experience) combined with mucilage, 

 and frequently with soluble animal matters. In alluvial soils distin- 

 guished for fertility, the soluble extract is found in the largest propor- 

 tion ; five parts of vegetable extract in four hundred of the soil is considered 

 the maximum for healthy vegetation. 



The soils called alluvial have the power, it is evident, of preserving this 

 substance in the decomposing vegetable matters which supply it, and of 

 gi\ing it out to the roots of plants, or rather to the water of the soil, 

 slowly, but in that seasonable and regular manner which is the most con- 

 ducive to the healthy exercise of the functions of the roots. It is evident 

 that in some alluvial soils this extractive vegetable matter must have re- 

 mained from a remote period uninjured for the purposes of vegetation*. 

 In siliceous, sandy, and gravelly soils, the reverse of this takes place, for 

 the manures applied to these is speedily decomposed, and the extractive 

 matter given out, comparatively, at once : hence the constant repetition 

 of manures required by these kinds of soil to keep them productive. When 

 clay, mild lime, or chalk, fine siliceous and calcareous sand, and impal- 

 pable vegetable matters are so intimately combined as to constitute what is 

 termed the best loam, the extractive matter, whether of long duration in 

 the soil or in recently supplied manure, is economized and given out to 

 \\ater, and to the roots of plants, in a similar degree of effectiveness as in 

 the alluvial soil : on the contrary, when clay is the chief earthy ingredient 

 of a soil, the vegetable matter is either retained in the manure, or given 

 out partially ; the lower temperature of the clay, its great adhesive powers, 

 and compact texture, uniting to produce this result f. The food of plants 

 supplied by atmospheric air, whatever proportion it may bear to that 

 supplied by the soil, is at least equally essential to the growth of plants, 

 for they can no more exist without that, than they can exist without the 

 soil. The curious structure of the leaves shews how admirably they are 



Extractive matter, when separated from the saline compounds with which it is usually 



accompanied in soils and in vegetable manures, and exposed to the air, soon decomposes or 



putiilies. It also losrs its solubility in water after t\vo or three solutions in and evapora- 



>f the water. It is aconstituent of the nutritive matter of the food of the larger domestic-. 



animals, hut in the process of digestion it is not retained in the hody of the animal for 



the purposes of Hie, but is voided with the fa-ces. The pasture grasses, corn, or annual 



vu or soiling plants, as clovers, lucerne, sainfoin, \etches, turnips, mangel 



1, and carrots, all contain e:\tr.ict as an essential constituent, which, with the woody 



.Hue matters of the vegetable, are returned again to the soil. 



t The Lfuat hem-lit resulting to clayey soils from the process of paring and burning, is 



that of improving their texture, and. even in some <K -give, their temperature or latent 



\vhat may be called a circulation of the water and air of a soil 



> r of preparing the food of plants depending on the soil. \Vherc 



Ll wanting, as in the case of a perfectly stagnant clay or peat, or a sandy soil, 



with a stil nous to water, vegetable matter, however ample, in these soils will 



1 atl'ord no support to trees, or. at least, they will not long exist if planted 



. such circumstances. So obvious is the ellect of this principle of circulation of 



llowcd the expiession.) that some ba\e undertaken to prove 



. depended on it alone, and that water and air constitute the 



Hants; and that even aniigal and vegetable matters were no farther useful 



than as contributing to the temperature- and texture of the soil, titling it for the more 



ready circulation of these, and more readily presenting them to the roots of plants. 



erroneous the conclusion D principle of practice inculcated by it is 



I IM ihe successful cultivation of trees, lor on it depend the processes of paring 



and burning, draining, trenching, digging, and in a word the judicious adoption of the 



various means which are emploj-fd fur pulverizing and comminuting soils. 





