PRACTICAL CULTURE OF PLANTS. 



673 



stimulating food for vegetables. To this may be 

 added, the excrements of animals. Horse and 

 cow dung is usually allowed by practical agri- 

 culturists to ferment and rot before it is applied 

 to the land ; though Sir II. Davy, on chemical 

 principles, recommends all such to be used in a 

 recent state. The dung of birds, especially of 

 those that feed on animal matter, is reckoned 

 highly stimulating manure. 



Li7ne. Calcareous and saline matters ai'e much 

 employed in vegetable culture. 



" Some inquirers," says Sir H. Davy, " adopt- 

 ing that sublime generalization of the ancient 

 philosophers, that matter is the same in essence, 

 and that the different substances considered as 

 elements by chemists, are merely different 

 arrangements of the same indestructible particles, 

 have endeavoured to prove, that all the varieties 

 of the principles found in plants may be formed 

 from the substances in the atmosphere, and that 

 vegetable life is a process in which bodies, that 

 the analytical philosopher is unable to change 

 or to form, are constantly composed and decom- 

 posed. But the general result of experiments 

 are very much opposed to the idea of the com- 

 position of the earths, by plants from any of the 

 elements found in the atmosphere or in water, 

 and tliere are various facts contradictory to the 

 idea." Jacquin states, that the ashes of glass- 

 wort, (saUola soda,) when it grows in inland 

 situations, afford the vegetable alkali ; when it 

 grows on the sea-shore, where compounds which 

 »fford soda are more abundant, it yields this 

 alkali. Duhamel found that plants which usu- 

 ally grow on the sea-shore, made small progress 

 when planted in soils containing little common 

 salt. The sun-flower, when growing in lands 

 containing no nitre, does not afford that sub- 

 stance, though, when watered by a solution of 

 nitre, it yields nitre abundantly. The table of 

 De Saussure shows that the ashes of plants are 

 similar in constitution to the soils in which they 

 have vegetated. TJiis philosopher made plants 

 grow in solutions of different salts, and he ascer- 

 tained, that in all cases certain portions of the 

 salts were absorbed l)y the plants, and found 

 unaltered in their organs. Even animals do not 

 appear to possess the power of forming the alka- 

 lies and earthy substances. Dr Fordyce found 

 that when canary birds, at the time tliey were 

 laying eggs, were deprived of access to carbonate 

 of lime, their eggs had soft shells. Yet, accord- 

 ing to the chemical analysis of Dr Marcet, the 

 quantity of phosphate and carbonate of lime 

 found in the bones of the chick, is much more 

 than that previously existing in the contents- of 

 the e^^, or the loss sustained by the shell. 



Lime, froni its strong attraction for carbonic 

 acid and moisture, may thus also be beneficial, 

 by affording a supply of both these to plants. 

 Lime exists in nature, and in the soil, in a state 



of combination witli carbonic acid. Limestone, 

 however, before it can be rendered friable, must 

 first be burnt and reduced to a quick or caustic 

 lime. In this state, on the addition of water, 

 it readily pulverizes, and greedily absorbs car- 

 bonic acid from the atmosphere. Very few 

 limestones or chalks, however, are pure, the 

 primary marbles and calcareous spars being the 

 exception. Clay, flint, magnesia, iron, and other 

 salts, are in greater or less quantity found mixed 

 in limestones. Slacked lime is a combination 

 of lime with about a third of its weight of water, 

 and is called a hydrate of lime, and when this 

 hydrate becomes, by exposure to air, a carbon- 

 ate, the excess of water is expelled. When 

 freshly burned or slacked lime is mixed -with 

 any moist fibrous vegetable matter, there is a 

 strong action between the lime and the vegetable 

 matter, and they form a kind of compost toge- 

 ther, of which a part is usually soluble in water. 

 By this kind of operation, lime renders matter, 

 which was before comparatively inert, nutritive; 

 and as charcoal and oxygen abound in all vege- 

 table matters, it becomes, at the same time, 

 converted into carbonate of lime. Jlild lime, 

 powdered limestone, marls, and chalk, have no 

 action of this kind upon vegetable matter ; they 

 destroy ^^■orms and other tender-skinned vermin, 

 and they prevent the too rapid decomposition ol 

 substances already dissolved, but in other re- 

 spects their operations are different from that of 

 quick lime. Lime, marls, and even shell-sand, 

 produce wonderful effects on peat soils, by 

 absorbing the gallic acid which they contain, 

 and promoting the decomposition of the woody 

 matters. 



All soils having a deficiency of calcareous 

 earth, and which do not effervesce with ncids, 

 are improved by lime, either mild or quicklime. 

 Sandy soils are improved more than clay. When 

 a soil deficient in calcareous matter contains 

 much soluble vegetable manure, the application 

 of quick lime should always be avoided, as it 

 either tends to decompose the soluble matters, 

 by uniting to them carbon and oxygen, so as to 

 become mild lime, or it combines with the 

 soluble matters, and forms compounds, liaving 

 less attraction for water than the pure vegetable 

 substance. The case is the same with regard to 

 most animal manures, but the operation of the 

 lime is different in different cases, and depends 

 upon the nature of the animal matter. Lime 

 forms a kind of insoluble soap with oily matters, 

 and then gradually decomposes them, by sepa- 

 rating from these ox^-gen and carbon. It com- 

 bines likewise with the animal acids, and proba- 

 bly assists their decomposition, by extracting 

 carbonaceous matter from them, combined witli 

 oxj-gen, and consequently it must render them 

 less nutritive. It tends to diminish likewise 

 the nutritive powers of albumen from the same 



