674 



HISTORY OF TIIIC VKGETABLK KINGDOM. 



causes, and always destroys, to a certain extent, 

 the efficacy of animal manures, either by com- 

 bining with certain of their elements, or by 

 giving to them new arrangements. Lime should 

 never bo applied with animal manures, nnless 

 they are too rich, or for the purpose of prevent- 

 ing noxious effluvia. It is injurious when mixed 

 with common dung, and tends to render the 

 extractive matter insoluble ; and with almost 

 all soft animal and vegetable substances, lime 

 foiTns insoluble composts, and thus destroys their 

 fermentative properties. Such compounds, how- 

 ever, exposed to the continued action of the air, 

 alter in course of time, the lime becomes a car- 

 bonate, and the animal and vegetable matter 

 enter by degrees into new compounds suited for 

 vegetable nourishment. In this view, lime pre- 

 sents two great advantages for the nutrition of 

 plants ; the first, that of disposing certain inso- 

 luble bodies to form soluble compounds ; the 

 second, that of prolonging the action and nutri- 

 tive qualities of substances beyond the tenn, 

 during which they would be retained, if these 

 substances were not made to enter into combina- 

 tion with lime. 



Impure lime, where the mixture is clay or 

 silex, is lessefficacious in proportion to theadmix- 

 ture, but these substances are not deleterious. 



Magnesia, on the other hand, has been deemed 

 hurtful to corn crops, although it may be found 

 advantageous in mixing with peat soils. Car- 

 l)onate of magnesia is deemed a useful constitu- 

 ent of soils. 



Gt/psum, orsulphate of lime,has been sometimes 

 npplied as a manure, but the exact nature of its 

 effects has been a subject of controversy. It has 

 been supposed by some persons to act by its 

 power of attracting moisture from the air ; but 

 this agency must be apparently insignificant. 

 When combined with water, it retains that fluid 

 too powerfully to yield it to the roots of the 

 plant, and its adhesive attraction for moisture is 

 inconsiderable ; the small quantity in which it is 

 used is also a circumstance hostile to this idea. 

 It has been erroneously said, that gypsum assists 

 the putrefaction of animal substances and the 

 decomposition of manure. The ashes of saint- 

 foin, clover, and ryegrass yield considerable quan- 

 tities of gypsum, and for such crops it is well 

 suited. The reason why gypsum is not generally 

 efficacious, is probably because most cultivated 

 soils contain it in sufficient quantities for the use 

 of the grasses. In the common course of culti- 

 vation, gypsum is furnished in the manure, for 

 it is contained in stable dung, and in the dung 

 of all cattle fed on grass, and it is not taken up 

 in corn crops, or crops of peas and beans, and in 

 very small quantities in turnip crops ; but where 

 lands are exclusively devoted to pasturage and 

 hay, it will be continually consumed. 



Phosphate of lime is a compound part of ani- 



mal and vegetable bodies; it is insoluble in pure 

 water, but is soluble in water containing any 

 acids. It constitutes the greater part of calcined 

 bones. It exists in most exerementitious sub- 

 stances, and is found both in the straw and grain 

 of wheat, barley, oats, and rye, and likewise 

 in beans, peas, and tares. Phosphate of lime is 

 generally conveyed to the land in the composi- 

 tion of other manure, and it is probably neces- 

 sary to corn and other crops. 



Wood ashes consist chiefly of potass united to 

 carbonic acid ; and as this is found in almost all 

 plants, its efficacy as an ingredient of the soil 

 is obvious. 



Common salt, which is a chloride of soda, is also 

 occasionally used as a manure. According to 

 Sir John Pringle, salt in small quantities assists 

 the decomposition of animal and vegetable mat- 

 ter. 



Soot contains ammoriia, an empj'reumatic oil, 

 and carbon or charcoal; it thus affords a power- 

 ful manure. On the whole. Sir H. Davy is of 

 opinion, that except the ammoniacal compounds, 

 or the compounds containing nitric, acetic, and 

 carbonic acid, none, of the saline substances can 

 afford, by decomposition, any of the common 

 principles of vegetation. The alkaline sulphates, 

 and the earthy muriates, are so seldom found in 

 plants, or are found in such minute quantities, 

 that it never can be an object to apply them to 

 the soil. 1'he earthy and alkaline substances 

 seem never to be formed in vegetation, and there 

 is every reason to believe, that they are never 

 decomposed ; for after being absorbed, they are 

 found in the ashes. The metallic bases of these 

 cannot exist in contact with aqueous fluids, and 

 these metallic bases, like other metals, have not 

 as yet been resolved into any other forms of 

 matter by artificial processes. They combine 

 readily with other elements, but tliey remain 

 indestructible, and can be traced undiminished 

 in quality through their diversified combina- 

 tions. 



The fermenting substances used in forming 

 hot beds are, statde litter or dung in a recent or 

 fresh state, tanner's bark, leaves of trees, grass, 

 and the herbaceous parts of jilants generally. 

 Stable dung is in the most general use for form- 

 ing hot beds, which are square masses of this 

 dung after it has undergone violent fennentation. 

 Tanners' bark is only preferred to dung, because 

 the substance which undergoes the process of 

 putrid fermentation requires longer time to 

 decay. Hence it is found useful in the baik 

 pits of hot houses, as requiring to be seldomer 

 removed or renewed than dung, or any other 

 known fermentable substance that can be pro- 

 cured in equal quantity. Leaves, and especially 

 oak leaves, come tlie nearest to bark, and have 

 the additional advantage, that when perfectly 

 rotten like dung, they form a rich mould or 



