Catalogue of Works on Gardenings §c. 127 



the soil (such as silicic or phosphoric acids) or are generated from nutriment 

 derived from the atmosphere. Hence, if these salts are not contained in the 

 soil, or if the bases necessary for their production be absent, they cannot be 

 formed ; or, in other words, plants cannot grow in such a soil. The juice, 

 fruit, and leaves of a plant cannot attain maturity, if the constituents necessary 

 for their formation are wanting, and salts must be viewed as such. These 

 salts do not, however, occur simultaneously in all plants. Thus, in saline 

 plants, soda is the only alkali found ; in corn plants, lime and potash form 

 constituents. Several contain both soda and potash, some both potash and 

 lime, whilst others contain potash and magnesia. The acids vary in a similar 

 manner. Thus one plant may contain phosphate of lime; a second, phosphate 

 of magnesia ; a third, an alkali combined with silicic acid ; and a fourth, an alkali 

 in combination with a vegetable acid. The respective quantities of the salts 

 required by plants are very unequal. The aptitude of a soil to produce one, 

 but not another, kind of plant, is due to the presence of a base which the 

 former requires, and the absence of that indispensable for the development of 

 the latter. Upon the correct knowledge of the bases and salts requisite for 

 the sustenance of each plant, and of the composition of the soil upon which 

 it grows, depends the whole system of a rational theory of agriculture; and 

 that knowledge alone can explain the process of fallow, or furnish us with the 

 most advantageous methods of affording plants their proper nourishment. 



" Give — so says the rational theory — to one plant such substances as are 

 necessary for its development ; but spare those which are not requisite, for the 

 production of other plants that require them. 



" It is the same with regard to these bases as it is with the water which is 

 necessary for the roots of various plants. Thus, whilst one plant nourishes 

 luxuriantly in an arid soil, a second requires much moisture, a third finds ne- 

 cessary this moisture at the commencement of its development, and a fourth 

 (such as potatoes) after the appearance of the blossom. It would be very 

 erroneous to present the same quantity of water to all plants indiscriminately. 

 Yet this obvious principle is lost sight of in the manuring of plants. An em- 

 pirical system of agriculture has administered the same kind of manures to all 

 plants ; or, when a selection has been made, it was not based upon a know- 

 ledge of their peculiar characters or composition. 



" The most important growth in England is that of wheat ; then of barley, 

 oats, beans, and turnips. Potatoes are only cultivated to a great extent in 

 certain localities ; rye, beet-root, and rape-seed, not very generally. Lucern 

 is only known in a few districts, whilst red clover is found universally. Now, 

 the selection of inorganic manures for these plants may be fixed upon by an 

 examination of the composition of their ashes. Thus, wheat must be cultivated 

 in a soil rich in silicate of potash. If this soil is formed from feldspar, mica, 

 basalt, clinkstone, or indeed of any materials which disintegrate with facility, 

 crops of wheat and barley may be grown upon it for many centuries in succes- 

 sion. But, in order to support an uninterrupted succession, the annual disin- 

 tegration must be sufficiently great to render soluble a quantity of silicate of 

 potash sufficient for the supply of a full crop of wheat or barley. If this is 

 not the case, the soil must either be allowed to lie fallow from time to time, 

 or plants may be cultivated upon it which contain little silicate of potash, or 

 the roots of which are enabled to penetrate deeper into the soil than corn 

 plants in search of this salt. During this interval of repose, the materials of 

 the soil disintegrate, and potash in a soluble state is liberated on the layers 

 exposed to the action of the atmosphere. When this has taken place, rich 

 crops of wheat may be again expected. 



" The alkaline phosphates, as well as the phosphates of magnesia and lime, are 

 necessary for the production of all corn plants. Now, bones contain the latter, 

 but none of the former, salts. These must, therefore, be furnished by means 

 of night-soil, or of urine, a manure which is particularly rich in them. Wood 

 ashes have been found very useful for wheat in calcareous soils ; for these 

 ashes contain both phosphate of lime and silicate of potash. In like manner 



