224 SCIENCE OF AGRICULTURE. Part II. 



the vine. It is merely, however, the ascending sap, and may be procured from almost any other plant by 

 thesame or similar means, and at the same season ; but particularly from the maple, birch, and walnut 

 tree, by means of boring a hole in the trunk. It issues chiefly from the porous and mixed tubes of the 

 alburnum ; though sometimes it does not flow freely till the bore is carried to the centre. A small branch 

 of a vine has been known to yield from twelve to sixteen ounces, in the space of twenty-four hours. A 

 maple tree of moderate size yields about 200 pints in a season, as has been already stated ; and a birch 

 tree has been known to yield, in the course of the bleeding season, a quantity equal to its own weight. In 

 the sap of Fagus sylvatica Vauquelin found the following ingredients : Water, acetate of lime with ex- 

 cess of acid, acetate of potass, gallic acid, tannin, mucous and extractive matter, and acetate of alumina. 

 In 1039 parts of the sap of the f/'lmus campi^stris he found 1027 parts of water and volatile matter, 9240 of 

 acetate of potass, r060 of vegetable matter, 796 of carbonate of lime, besides some slight indications of 

 the presence of sulphuric and muriatic acids ; and at a later period of the season he found the vegetable 

 matter increased, and the carbonate of lime and acetate of potass diminished. From the above experi- 

 ments therefore, as well as from those of other chemists, it is plain that the sap consists of a great 

 variety of mgredients, differing in different species of plants ; though there is too little known concerning 

 it to warrant the deduction of any general conclusions, as the number of plants whose sap has been hitherto 

 analysed is but very limited. It is the grand and principal source of vegetable ahment, and may be 

 regarded as being somewhat analogous to the blood of animals. It is not made use of by man, at least in 

 its natural state : but there are trees, such as the birch, whose sap may be manufactured into a very 

 pleasant wine ; and it is well known that the sap of the American maple tree yields a considerable 

 quantity of sugar. 



1496. The proper jm'ce. When the sap has received its last degree of elaboration from the diflferent or- 

 gans through which it has to pass, it is converted into a peculiar fluid, called the proper juice. This fluid 

 may be distinguished from the sap by means of its colour, which is generally green, as in periwinkle ; or 

 red, as in logwood ; or white, as in spurge ; or yellow, as in celandine ; from the last two of which it may 

 readily be obtained by breaking the stem asunder, as it will then exude from the fracture. Its principal 

 seat is in the bark, where it occupies the simple tubes ; but sometimes it is situated between the bark and 

 wood, as in the juniper tree ; or in the leaf, as in the greater parts of herbs ; or it is diffused throughout 

 the whole plant, as in the fir and hemlock ; in which case, either the proper juice mixes with the sap, or 

 the vessels containing it have ramifications so fine as to be altogether imperceptible. It is not, however, 

 the same in all plants, nor even in the different parts of the same plant. In the cherry tree it is mucila- 

 ginous ; in the pine it is resinous ; in spurge and celandine it is caustic, though resembling in appearance 

 an emulsion. In many plants the proper juice of the bark is different from tliat of the flower ; and the 

 proper juice of the fruit different from both. Its appearance under the microscope, according to Senebier, 

 is that of an assemblage of small globules connected by small and prism-shaped substances placed between 

 them. If this juice could be obtained in a state of purity, its analysis would throw a considerable degree 

 of light upon the subject of vegetation ; but it seems impracticable to extract it without a mixture of 

 sap. Senebier analysed the milky juice of Euphorbia 6'yparissias, of which, though its pungency was 

 so great as to occasion an inflammation of the eyes to the person employed to procure it, he had obtained 

 a small quantity considerably pure. It mixed readily with water, to which it communicated its colour. 

 When left exposed to the air, a slight precipitation ensued; and, when allowed to evaporate, a thin and 

 opaque crust remained behind. Alcohol coagulated it into small globules. Ether dissolved it entirely, as 

 did also oil of turpentine. Sulphuric acid changed its colour to black ; nitric acid to green. The most 

 accurate experiments on the subject are those of Chaptal. When oxymuriatic acid was poured into the 

 peculiar juice of Euphorbia, a very copious white precipitate fell down, which, when washed and dried, 

 had the appearance of starch, and was not altered by keeping. Alcohol, aided by heat, dissolved two 

 thirds of it, which the addition of water again precipitated. They had all the properties of resin. The 

 remaining third part possessed the properties of woody fibre. The same experiment was tried on the juice 

 of a variety of other plants, and the result uniformly was that oxymuriatic acid precipitated from them 

 woody fibre. 



1497. The virtues of plants have generally been thought to reside in their proper juices, and the opinion 

 seems indeed to be well founded. It is at least proved by experiment in the poppy, spurge, and fig. The 

 juice of the first is narcotic, of the last two corrosive. The diuretic and balsamic virtues of the fir reside 

 in its turpentine, and the purgative property of jalap in its resin. If sugar is obtained from the sap of the 

 sugar-cane and maple, it is only because it has been mixed with a quantity of proper juice. The bark 

 certainly contains it in greatest abundance, as may be exemplified in cinnamon and quinquina. But the 

 peach tree furnishes an exception to this rule : its flowers are purgative, and the whole plant aromatic ; 

 but its gum is without any distinguished virtues. Malpighi regarded the proper juice as the principle 

 of nourishment, and compared it to the blood of animals ; but this analogy does not hold very closely. 

 The sap is perhaps more analogous to the blood, from which the proper juice is rather a secretion. In 

 one respect, however, the analogy holds good, that is, with regard to extravasated blood and peculiar 

 juices. If the blood escapes from the vessels it forms neither flesh nor bones, but tumours ; and if the pro- 

 per juices escape from the vessels containing them, they form neither wood nor bark, but a lump or 

 deposit of inspissated fluid. To the sap or to the proper juice, or rather to a mixture of both, we must 

 refer such substances as are obtained from plants under the name of expressed juices, because it is evident 

 that they can come from no other source. In this state they are generally obtained in the first instance, 

 whether with a view to their use in medicine or their application to the arts. It is the business of the 

 chemist or artist to separate and purify them afterwards, according to the peculiar object he may happen 

 to have in view, and the use to which he purposes to apply them. They contain, like the sap, acetate of 

 potass or of lime, and assume a deeper shade of colour when exposed to the fire or air. The oxymuriatic 

 acid precipitates from them a coloured and flaky substance as from the sap, and they yield by evaporation 

 a quantity of extract ; but they differ from the sap in exhibiting no traces of tannin or gallic acid, and 

 but rarely of the saccharine principle. 



1498. Ashes. When vegetables are burnt in the open air the greatest part of their substance is evapo- 

 rated during the process of combustion ; but ultimately there remains a portion which is altogether 

 incombustible, and incapable of being volatilised by the action of fire. This residuum is known by the 

 name of ashes. Herbaceous plants, after being dried, yield more ashes than woody plants ; the leaves 

 more than the branches ; and the branches more than the trunk. The alburnum yields also more ashes 

 than the wood ; and putrefied vegetables yield more ashes than tiie same vegetables in a fresh state, if the 

 putrefaction has not taken place in a current of water. The result of Saussure's experiments on 1000 parts 

 of different plants was as follows : 



Gathertd in May, dried leaves of the oak ----- 53 partt of ashes. 



green leaves of the oak - - - - 13 



dried leaves of the Rhododendron - - - 50 



dried leaves of the .iS/sculus HipBocistanum - 72 



trunk and branches of .<3E'sculus Hippoc^tanum 35 



Gathered in September, dried leaves of the .(E'sculus Hippocdstanum 86 



dried leaves of the oak - - - - 55 



green leaves of the oak - - - - 24 



Gathered when injlower, leaves of Pisum sativum - - - 95 



Gathered when in fruit, leaves of Pisum sativum - - - 81 



leaves of Faba vulgaris - - - 20 



Gathered liefore coming into flower, the leaves of the Fkba Tulgkris 16 



Oak, the dried bark 60, the alburnum 4, wood . . - - 2 



