845. The object of manuring is mainly to increase the quantity of organic matter, or to restore to the soil those qualities which have been taken away by the crops. By various amendments (as gypsum, lime, charcoal) ammonia is strongly attracted from the air and yielded again to vegetation. Marl promotes the decomposition of the soil, and ashes add to the potassa - a substance which also exists naturally in soils, being derived from the decomposition of the rocks which contain it, as granite, clay-slate, basalt, etc.

846. Bone manure is rich in the phosphates indispensable in the formation of albumine, gluten, and other blood-making qualities of fruits. The mineral phosphate of lime, bone-chalk, etc., are of the same nature.

847. Guano is a manure whose great value depends upon its abundant nitrates and ammoniacal salts. It is the excrement of sea-fowl which has for ages accumulated in vast deposits on certain coasts and islands of South America and Africa.

848. Fallow ground. Soils are often improved by lying fallow for a season, thus allowing time to form, by decomposition, a fresh supply of that particular ingredient which had been exhausted by previous crops. On the same principle is explained the beneficial effects of a rotation of such crops as require different mineral substances in their composition.

849. Light and heat. After all these materials have been supplied to the plant, still two other agents are requisite, without which the great work of vegetation will not go on. These life-giving principles are light and heat, both of which emanate in floods from the sun. Under their influence the raw material is received into the vessels of the plant and assimilated to its own substance - a process which can be fully comprehended only by Him whose power is adequate to carry it on.

850. Digestion. Under the influence of solar light and a temperature above the freezing point, water holding various earths in solution is imbibed by the roots and raised into the tissues of the stem, dissolving as it passes small portions of gum or sugar previously deposited there. In this state it is crude sap. Passing on it enters the leaves, and is there subjected to the action of the chlorophylle (§ 657) which chiefly constitutes the apparatus of digestion. Here it is concentrated by transpiration, sending off quantities of pure water. Meanwhile the leaves are imbibing carbonic acid from the air, decomposing it, retaining the carbon, and returning pure oxygen. Thus elaborated, the sap is now called

851. The proper juice, consisting evidently of carbon and water, with a little nitrogen and minute portions of the mineral substances mentioned above. From this, the vital fluid, are elaborated the building material of the vegetable fabric, and all its various products and secretions.

852. Protein, or protoplasm, the substance of the primordial utricle, analogous in composition to the living tissues of animals, and containing nitrogen, is organized, first of all, from this vital fluid. Cellulose (or lignin) next, the peculiar principle of vegetable tissue, whether cellulal, vasoular, or woody, consisting of carbon with the exact elements of water, viz., C12 H10 O10. Then, through the action of light, chlo-rophylle springs into being, clothing the plant in living green Meanwhile

853. Gum, starch and sugar, nutritive products common to all plants, are also developed from the proper juice - not all to be immediately employed in building up the tissues, but mostly to be stowed away in reserve for future use. Such deposits are made in the root of the beet, tuber of the potato, and in the fruit generally. These three products, with cellulose, are all composed of carbon and the elements of water, often in identical proportions; thus cane sugar is C12 H12 O12; grape sugar, C12 H11 O11; gum, C12 H10 O10; starch, C12 H10 O10; cellulose, C12 H10 O10.

854 Sugar is sometimes produced directly from the proper juice, as in the root of beet, stalk of maize, and sugar-cane; but oftener, during germination, from the starch deposited in the seed. Its composition, as seen above, differs from that of starch only in containing a larger proportion of the elements of water or (what is the same) a smaller proportion of carbon. As starch is insoluble, its transformation into soluble gum or sugar is needful to render it available for the nutrition of the growing embryo.

855. The facility with which these FIVE general products are con-verted into each other, both in the growing plant and in the laboratory of the chemist, is accounted for by the similarity of their chemical condition. Thus starch, gum and cellulose may reconvert merely by some change in the arrangement of their constituent atoms, or they may become sugar by the addition of one or two atoms of water.

856. Among the numerous secretions of plants, which our limits forbid us to consider, are the vegetable acids containing more oxygen proportionately than exists in water; the oily acids, resins and oils, containing less oxygen than exists in water, or none at all These substances vary in the different species almost to infinity, taking into their constitution, in addition to the four organogens, minute portions of the mineral substances introduced by rain and river water. Their peculiarities of odor, flavor, color, properties, etc., although so obvious to the senses, are occasioned by differences of constitution often so slight as to elude the most delicate tests of the chemist.

857. The following table contains examples of the various classes of secretions, arranged in reference to their relative proportion of oxygen:-

CLASS.

NAME AND SOURCE.

FORMULA.

Acids highly oxygenized.

Oxalic, Leaves of rhubarb, sorrel, etc ......

C2 H O4

The proportion of oxygen to hydrogen is greater than in water.

Citric, Fruit of the Orangeworts .................

C12 H8 O14

Malic, Apples and many fruits ...................

C8 H6 O10

Tartaric, Juice of grapes .....................

C8 H6 O12

Gallic, Nutgalls ..................................

C14 H6 O10

Tannic, Astringent barks, nutgalls,.......

C13 H6 O8?

Meconic, Juice of the Poppy worts,.......

C14 H4 Ol4

Neutral substances. Mild, nutritious.

Grape sugar. Grapes, raisins, honey,....

C12 H12 O12

The oxygen proportioned to hydrogen equally, as in water.

Cane sugar. Maple, maize, sorghum,.....

C12 H11 O11

Starch, In allplants ......................

C12 H10 O10

Gum, mucilage. Common,.............

C12 H10 O10

Cellulose. Substance of cellular membrane,

C12 H10 O10

CLASS.

NAME AND SOURCE.

FORMULA.

Neutral prin-ciples, bitter, acrid, coloring.

Phloridein. Bark of cherry, apple, etc.,...

C12 H7 06

Oxygen in proportion slightly less than water.

Salicine. Bark of willow,................

C13 H9 O7

Populine. Bark of aspen (Populus),.....

C20 H11 O8

Meconine. Juice of poppy,....................

C10 H5 O4

Alizarine (Turkey red). Madder,........

C37 H12 O10

Essential, volatile oils, oxygenated.

Oil of anise. Pimpinella anisum,........

C16 H8 O4

Oxygen in diminished proportion.

Oil of cinnamon. Laurus cinnamomum,..

C18 H8 O2

Oil of clover. Caryophyllus aromaticus,..

C24 H15 O5

Oil of sassafras. Laurus sassafras,........

C10 H5 O2

Oil of peppermint. Mentha piperita,.....

C24 H20 O2

Oil of valerian. Valeriana officinalis,.....

C12 H10 O2

Volatile acids derived from oils.

Valeric acid. Root of valerian,........................

C10 H10 O4

In this series the proportion of oxygen regularly diminishes.

Enanthylic. Castor-oil nut,............

C14 H14 O4

Pelargonic. Rose geranium.......................

C18 H18 O4

Lauric. Laurus nobilis,.....................

C24 H24 O4

Myristic. Nutmegs,.......................

C28 H28 O4

Behmic,.........................

C44 H44 O4

Melissic,...............................

C60 H60 O4

Resins, gum-resins, balsams, and camphors.

Colophony, or resin of pine, etc.,..................

C20 H14 O2

very little oxygen remaining.

Resin of Copaiva. Copaifera,.......................

C40 H31 O4

Resin of Mastic. Pistacia lentiscus,....................

C40 H31 O2

Resin of Copal. Hymmaea, etc.,.....................

C40 H31 O3

Camphor. Laurus camphora,.....................

C20 H16 O2

Borneo camphor. Dryobalanops,.................

C20 H18 O2

Volatile oils, non-oxygenized.

Oil of trupentine. Pines,.........................

C5 H4

Carbo-hy-drogens, isomeric, destitute of oxygen.

Bergamot. A veriety of orange,........................

C5 H4

Black pepper. Piper nigrum,...............

C5 H4

Juniper, savine. Juniperus,...............

C5 H4

Parsley, cubebs, etc.,......................

C5 H4

Oxygenated alkaloids.

Quinine. Peruvian bark.,........................

C23 H22 O4 N2

Oxygen less than hydrogen.

Morphine. Opium, poppy,....................

C34 H19 O6 N

Theine. Leaves of the tea-plant,......................

C66 H10 O4 N4

Alkalolds.

Nicotine. Tobacco (Nicotiana).........

C20 H14 N2

Oxygen none.

Coneine. Hemlock (Conium),......................

C16 H15 N

Volatile.

Oil of mustard. Sinapis nigra,..........

C16 H5 N S2

Oxygen none.

Oil of horse-radish. Cochlearia,.........................

C16 H5 N S2

Oil of garlic. Allium sativum,..................

C6 H5 S

Organic compounds.

Protein. Primoridal utricle,......................

C86 H25 O10 N4

=Pr.

Gluten. The cereal grains,......................

10 Pr+S

Casein. Leguminous seeds,...................

10 Pr + P + S

Albumen. Many seeds,......................

10 Pr + P + 2S