Diastase is the name applied to a substance existing in malt, and obtained by macerating that substance with cold water, and adding a quantity of alcohol to the fluid, when the diastase is immediately precipitated in white flocks. It is produced during the malting process, and is not found in the unmalted barley. Its chemical composition is unknown, but it is nitrogenous, and is believed to be produced by the decomposition of gluten. If a very small quantity of diastase be mixed with starch suspended in hot water, the starch is found gradually to dissolve, and to pass first into the state of dextrine, then into that of sugar. The change thus effected takes place also in a precisely similar manner in the plant, diastase being produced during the process of germination of all seeds and tubers, for the purpose of effecting this change, and to fulfil other functions less understood, but no doubt equally important. Diastase is found in the seeds only during the period when the starch they contain is passing into sugar; as soon as that change has taken place, its function is ended, and it disappears.



CHAPTER III.

THE CHANGES WHICH TAKE PLACE IN THE FOOD OF PLANTS DURING THEIR GROWTH.

The simple compounds which the plant absorbs from the atmosphere and soil are elaborated within its system, and converted into the various complex substances of which its tissues are composed, by a series of changes, the details of which are still in some respects imperfectly known, although their general nature is sufficiently well understood. They may be best rendered intelligible by reference, in the first instance, to the changes occurring during germination, when the young plant is nourished by a supply of food stored up in the seed, in sufficient quantity to maintain its existence until the organs by which it is afterwards to draw its nutriment from the air and soil are sufficiently developed to serve that purpose.

Changes occurring during Germination.—When a seed is placed in the soil under favourable circumstances, it becomes the seat of an important and remarkable series of chemical changes, which result in the production of the young plant. Experiment and observation have shown that heat, moisture, and air, are necessary to the production of these changes, and though probably not absolutely essential, the absence of light is favourable in the early stages. The temperature required for germination varies greatly in different seeds, some germinating readily at a few degrees above the freezing point, and others requiring a tolerably high temperature. The rapidity with which it takes place appears to increase with the temperature; but this is true only within very narrow limits, for beyond a certain point heat is injurious, and when it exceeds 120 deg. or 130 deg. Fahrenheit, entirely prevents the process. The presence of oxygen is also essential, for it has been shown that if seeds are placed in a soil exposed to an atmosphere deprived of that element, or if they be buried so deep that the air does not reach them, they may lie without change for an unlimited period; but so soon as they are exposed to the air, germination immediately commences. Illustrations of this fact are frequently observed where earth from a considerable depth has been thrown up to the surface, when it often becomes covered with plants not usually seen in the neighbourhood, which have sprung from buried seeds. When all the necessary conditions for germination are fulfilled, the seed absorbs moisture, swells up, and sends out a shoot which rises to the surface, and a radicle which descends—the one destined to develop the leaves, the other the roots, by which the plant is afterwards to derive its nutriment from the air and the soil. But until these organs are properly developed, the plant is dependent on the matters contained in the seed itself. These substances are mostly insoluble, but are brought into solution by the atmospheric oxygen acting upon the gluten, and converting it into a soluble substance called diastase, which in its turn reacts upon the starch, converting it first into dextrine, and then into cellulose, and the latter is finally deposited in the form of organised cells, and produces the first little shoot of the plant. At the first moment of germination, the oxygen absorbed appears simply to oxidize the constituents of the seed, but this condition exists only for a very limited period, and is soon followed by the evolution of carbonic acid, water being at the same time formed from the organic constituents of the seed, which gradually diminishes in weight. The amount of this diminution is different with different plants, but always considerable. Boussingault found that the loss of dry substance in the pea amounted in 26 days to 52 per cent, and in wheat to 57 per cent in 51 days. Against this, of course, is to be put the weight of the young plant produced; but this is never sufficient to counterbalance the diminished weight of the seed, for Saussure found that a horse bean and the plant produced from it weighed, after 16 days, less by 29 per cent than the seed before germination. The same phenomenon is observed in the process of malting, which is in fact the artificial germination of barley, the malt produced always weighing considerably less than the grain from which it was obtained. It was believed by Saussure, and the older investigators, that the carbonic acid evolved was entirely produced from starch and sugar; and as these substances may be viewed as compounds of carbon and water, the change was very simply explained by supposing that the carbon was oxidised and converted into carbonic acid and its water eliminated. But this hypothesis is incapable of explaining all the phenomena observed; for woody fibre, which is one of the chief constituents of the young plant, contains more carbon than the starch and sugar from which it must have been produced, and we are, therefore, forced to admit that the action must be more complicated. There is every reason to believe that the nitrogenous constituents of the seed are most abundantly oxidized, for they are remarkably prone to change; but the action of the air is not confined to them, and it appears most probable that all the substances take part in the decomposition, and the process of germination may, in some respects, be compared to decay or putrefaction, which, like it, is attended by the absorption of oxygen and evolution of carbonic acid; but while in the latter case the residual substances remain in a useless state, in the former they at once become part of a new organism.

Changes occurring during the After-growth of the Plant.—When the plant has developed its roots and leaves, and exhausted the store of materials laid up for it in the seed, it begins to derive its subsistence from the surrounding air, and to absorb carbonic acid, water, ammonia, and nitric acid, and to decompose and convert them into the different constituents of its tissues. These changes take place slowly at first, and more rapidly as the organs fitted for the elaboration of its food are developed. The roots and the leaves are equally active in performing this duty, the former absorbing the mineral matters along with the carbonic acid, ammonia, nitric acid, and moisture in the soil, or the manure added to it; the latter gathering the gaseous substances existing in the air. Each of these undergoes a series of changes claiming our consideration.

Decomposition of Carbonic Acid.—Carbonic acid, which appears to be absorbed with equal readiness by the roots, leaves, and stems, undergoes immediate decomposition, its carbon being retained, and its oxygen, in whole or in part, evolved into the air. This decomposition occurs only under the action of the sun's rays, and has been found to be proportionate to the amount of light to which the plant is exposed. It takes place only in the green parts of plants, for though the roots absorb carbonic acid, they cannot decompose it, or evolve oxygen; and the coloured parts, the flowers, fruits, etc., have an entirely opposite effect, absorbing oxygen and giving off carbonic acid. The absorption of carbonic acid and escape of oxygen has been proved by numerous direct experiments by Saussure and others, in which both atmospheric air and artificial mixtures containing an increased quantity of carbonic acid have been employed. Saussure allowed seven plants of periwinkle (Vinca minor) to vegetate in an atmosphere containing 7.5 per cent of carbonic acid for six days, during each of which the apparatus was exposed for six hours to the sun's rays. The air was analysed both before and after the experiment, and the results obtained were—

Volume Carbonic of the air. Nitrogen. Oxygen. Acid. Before the experiment, 5746 4199 1116 431 After " 5746 4338 1408 0 —— —— —— —— Difference, 0 +139 +292 -431

In this experiment the whole of the carbonic acid, amounting to 431 volumes, was absorbed, but only 292 volumes of oxygen were given off. Had the carbonic acid been entirely decomposed, and all its oxygen eliminated, its volume would have been equal to that of the acid, or 431, so that in this instance 139 volumes of the oxygen of the carbonic acid have been retained to form part of the tissues of the plant. On the other hand, the nitrogen is found to be increased after the experiment. It might be supposed that the nitrogen evolved had been derived from the decomposition of the nitrogenous constituents of the plant, but this cannot be the true explanation, because in this particular case it greatly exceeded the whole nitrogen contained in the plants experimented on. Its source is not well understood, but Boussingault supposes it to have existed in the interstices of the plant, and to have escaped during the course of the experiment. Saussure found that the oak, the horse-chesnut, and other plants, absorb oxygen and give off carbonic acid in less volumes than the oxygen, while the house-leek and the cactus absorb oxygen without evolving carbonic acid. The absorption and decomposition of carbonic acid takes place only during the day, and matters are entirely reversed during the night, when oxygen is absorbed and carbonic acid eliminated from all parts of the plants.

Although the action occurring during the night is the reverse of that which takes place during the day, it is in no degree to be attributed to a re-oxidation of the carbon which had been deposited in the tissues of the plant. It appears, on the contrary, to be a purely mechanical, and not a chemical process. During the night the sap continues to circulate through the vessels of the plant, and moisture, carrying with it carbonic acid in solution, is absorbed by the roots; but when it reaches the leaves, where the sun's light would have caused its decomposition during the day, it is again exhaled unchanged. The oxygen absorbed during the night must, however, take part in some chemical processes, for if it were merely mechanical, the absorption would not be confined to that gas alone, but would be participated in by the other constituents of the air. Moreover, the amount of absorption varies greatly in different plants—being scarcely appreciable in some, and very abundant in others. Plants containing volatile oils, which are readily converted into resins by the action of oxygen, or those containing tannin or other readily oxidizable substances, take up the largest quantity. This is remarkably illustrated by an experiment in which the leaves of the Agave americana, after twenty-four hours' exposure in the dark, were found to have absorbed only 0.3 of their volume of oxygen, while those of the fir, in which volatile oil is abundant, had taken up twice, and those of the oak, containing tannin, eighteen times as much oxygen.

In the flowers, both by day and night, there is a constant absorption of oxygen, and evolution of carbonic acid. In fact, an active oxidation is going on, attended by the evolution of heat, which, in the Arum maculatum and some other plants, is so great as to raise the temperature of the flower 10 deg. or 12 deg. above that of the surrounding air.

Decomposition of Water in the Plant.—In addition to the function which water performs in the plant, as the solvent of the different substances which form its nutriment, and hence as the medium through which they pass into its organs, it serves also as a direct food, undergoing decomposition, and yielding hydrogen to the organic substances. Its constituents, along with those of the carbonic acid absorbed, undergo a variety of transformations, and form the principal part of the non-nitrogenous constituents. It has been already observed that starch, sugar, and the other allied substances, may be considered as compounds of carbon with water; and they might be supposed to owe their origin to the carbonic acid losing the whole of its oxygen, and direct combination then ensuing between the residual carbon and a certain proportion of water; but this would imply that the latter substance undergoes no decomposition, and though undoubtedly the simplest view of the case, it is by no means the most probable. It is much more likely that the carbonic acid is only partially decomposed, half its oxygen being separated, and replaced by hydrogen, produced by the decomposition of a certain quantity of water into its elements. Thus, for instance, sugar may be produced from twelve equivalents of carbonic acid and twelve equivalents of water, twenty-four equivalents of oxygen being eliminated, as thus represented:

12 equivalents of carbonic acid, C_{12}O_{12}O_{12} 12 " water, H_{12}O_{12} 1 " sugar, and 24 of ox. C_{12}H_{12}O_{12} + O_{24}

It must not be supposed that we are in a condition to assert that sugar is really produced in the manner here shown, the illustration being given merely for the purpose of pointing out how it may be supposed to occur, and on a similar principle it is possible to explain the formation of most other vegetable compounds; and this subject has been very fully discussed by the late Dr. Gregory, in his "Handbook of Organic Chemistry." That water must be decomposed, is evident from the fact, established by analysis, that the hydrogen of the plant generally exceeds the quantity required to form water with its oxygen, so that this excess at least must be produced by the decomposition of water. The hydrogen of the volatile oils, many of which contain no oxygen, and that of the fats, which contain only a small quantity, must manifestly be obtained in a similar manner.

Decomposition of Ammonia.—The nitrogenous or albuminous compounds of vegetables must necessarily obtain their nitrogen from the decomposition either of ammonia or nitric acid, experiment having distinctly shown that they are incapable of absorbing it in the free state from the atmosphere. It has been clearly ascertained that the albuminous substances do not contain ammonia, and it is hence apparent that a complete decomposition of that substance must take place in the plant. No doubt carbonic acid and water take part with it in these changes, which must be of a very complex character, and in the present state of our knowledge it seems hopeless to attempt any explanation of them.

Decomposition of Nitric Acid.—Chemists are not entirely at one as to whether nitric acid is directly absorbed by the plant, or is first converted into ammonia. But there are certain facts connected with the chemistry of the soil, to be afterwards referred to, which seem to us to leave no doubt that it may be directly absorbed; and in that case it must be decomposed, its oxygen being eliminated, and the nitrogen taking part with carbon and hydrogen in the formation of the organic compounds. It must be clearly understood that while such changes as those described manifestly must take place, the explanations of them which have been attempted by various chemists are not to be accepted as determinately established facts; they are at present no more than hypothetical views which have been expressed chiefly with the intention of presenting some definite idea to the mind, and are unsupported by absolute proof; they are only inferences drawn from the general bearings of known facts, and not facts themselves. Although, therefore, they are to be received with caution, they have advantages in so far as they present the matter to us in a somewhat more tangible form than the vague general statements which are all that could otherwise be made.



CHAPTER IV.

THE INORGANIC CONSTITUENTS OF PLANTS.

When treating of the general constituents of plants, it has been already stated that the older chemists and vegetable physiologists, misled by the small quantity of ash found in them, entertained the opinion that mineral matters were purely fortuitous components of vegetables, and were present merely because they had been dissolved and absorbed along with the humus, which was then supposed to enter the roots in solution, and to form the chief food of the plant. This supposition, which could only be sustained at a time when analysis was imperfect, has been long since disproved and abandoned, and it has been distinctly shown by repeated experiment that not only are these inorganic substances necessary to the plant, but that every one of them, however small its quantity, must be present if it is to grow luxuriantly and arrive at a healthy maturity. The experiments of Prince Salm Horstmar, before alluded to, have established beyond a doubt, that while a seed may germinate, and even grow, to a certain extent, in absence of one or more of the constituents of its ash, it remains sickly and stunted, and is incapable of producing either flower or seed.

Of late years the analysis of the ash of different plants has formed the subject of a large number of laborious investigations, by which our knowledge of this subject has been greatly extended. From these it appears that the quantity of ash contained in each plant or part of a plant is tolerably uniform, differing only within comparatively narrow limits, and that there is a special proportion belonging to each individual organ of the plant. This fact may be best rendered obvious by the subjoined table, showing the quantity of ash contained in a hundred parts of the different substances dried at 212 deg.. Most of these numbers are the mean of several experiments:—

Table showing the quantity of inorganic matters in 100 parts of different plants dried at 212 deg..

SEEDS.

Wheat 1.97 Barley 2.48 Oats (with husk) 3.80 Oats (without husk) 2.06 Rye 2.00 Millet 3.60 Rice 0.37 Maize 1.20 Peas 2.88 Beans 3.22 Kidney Beans 4.09 Lentils 2.51 Tares 2.60 Buckwheat 2.13 Linseed 4.40 Hemp seed 5.60 Rape seed 4.35 Indian Rape-seed[A] 4.06 Sunflower 3.26 Cotton seed 5.93 Guinea Corn 1.99 Gold of Pleasure 4.10 White Mustard 4.15 Black Mustard 4.31 Poppy 6.56 Niger seed (Guizotia oleifera) 7.00 Earth nut 3.88 Sweet Almond 4.90 Horse-chesnut 2.81 Grape 2.76 Clover 6.19 Turnip 3.98 Carrot 10.03 Sainfoin 5.27 Italian Ryegrass 6.91 Mangold-Wurzel 6.58

STRAWS AND STEMS.

Wheat 4.54 Barley 4.99 Oat 7.24 Winter Rye 5.15 Summer Rye 5.78 Millet 8.32 Maize 3.60 Pea 4.81 Bean 6.59 Tares 6.00 Lentil 5.38 Buckwheat 4.50 Hops 4.42 Flax straw 4.25 Hemp 4.14 Gold of Pleasure 6.05 Rape 4.41 Potato 14.90 Jerusalem Artichoke 4.40

ENTIRE PLANT.

Potato 17.70 Spurry 10.06 Red Clover 8.79 White Clover 8.72 Yellow Clover 8.56 Crimson Clover (T. incarnatum) 10.81 Cow Grass (T. medium) 11.31 Sainfoin 6.51 Ryegrass 6.42 Meadow Foxtail (Alopecurus pratensis) 7.81 Sweet-scented Vernal Grass (Anthoxanthum odoratum) 6.32 Downy Oat Grass (Avena pubescens) 5.22 Bromus erectus 5.21 Bromus mollis 5.82 Cynosurus cristatus 6.38 Dactylis glomeratus 5.31 Festuca duriuscula 5.42 Holcus lanatus 6.37 Hordeum pratense 5.67 Lolium perenne 7.54 Poa annua 2.83 Poa pratensis 5.94 Poa trivialis 8.33 Phleum pratense 5.29 Plantago lanceolata 8.68 Poterium Sanguisorba 7.97 Yarrow 13.45 Rape Kale 8.00 Cow Cabbage 10.00 Asparagus 6.40 Parsley 1.10 Furze 3.11 Chamomile (Anthemis arvensis) 9.66 Wild Chamomile (Matricaria Chamomilla) 9.10 Corn Cockle (Agrostemma Githago) 13.20 Corn Blue Bottle (Centaurea Cyanus) 7.32 Foxglove 10.89 Hemlock (Conium maculatum) 12.80 Sweet Rush (Acorus Calamus) 6.90 Common Reed (Arundo Phragmites) 1.44 Celandine (Chelidonium majus) 6.85 Equisetum fluviatile 23.60 Equisetum hyemale 11.80 " arvense 13.80 " linosum 15.50 Fucus nodosus 19.03 Fucus vesiculosus 27.63 Laminaria digitata 39.68

LEAVES.

Turnip 9.37 Beet 20.30 Kohl-rabi 18.54 Carrot 10.95 Jerusalem Artichoke 28.30 Hemp 22.00 Hop 17.25 Tobacco 22.62 Spinach 19.76 Chicory 15.67 Poplar 23.00 Red Beech 6.00 White Beech 10.51 Oak 9.80 Elm 16.33 Horse-chesnut 9.08 Maple 28.05 Ash 14.76 Fir 2.31 Acacia 18.20 Olive 6.45 Orange 13.73 Potato 15.10 Tussac Grass 7.15

ROOTS AND TUBERS.

Potato 4.16 Jerusalem Artichoke 5.38 Turnip 13.64 Beet 8.27 Kohl-rabi 6.08 Rutabaga 7.34 Carrot 5.80 Belgian White Carrot 6.22 Mangold-Wurzel 8.78 Parsnip 5.52 Radish 7.35 Chicory 5.21 Madder 8.33

WOODS.

Beech 0.38 Apple 1.29 Cherry 0.28 Birch 1.00 Oak 2.50 Walnut 1.57 Lime 5.00 Horse-chesnut 1.05 Olive 0.58 Mahogany 0.81 Vine 2.57 Larch 0.32 Fir 0.14 Scotch Fir 0.17 Filbert 0.50 Chesnut 3.50 Poplar 0.80 Hazel 0.50 Orange 2.74 Vine 2.57

BARKS.

Beech 6.62 Cherry 10.37 Fir 1.79 Oak 6.00 Horse-chesnut 7.85 Filbert 6.20 Cork 1.12

FRUITS.

Plum 0.40 Cherry 0.43 Strawberry 0.41 Pear 0.41 Apple 0.27 Chesnut 0.99 Cucumber 0.63 Vegetable Marrow 5.10

On examining this table it may be observed that, notwithstanding the very great variety in the proportion of ash in different plants, some general relations may be traced. A certain similarity may be observed between those belonging to the same natural family, the seeds of all the cereal grains, for instance, containing in round numbers two per cent of inorganic matters. Leguminous seeds (peas and beans) contain about three per cent, while in rape-seed, linseed, and the other oily seeds, it reaches four per cent. In the stems and straws less uniformity exists, but with the exception of a few extreme cases, the quantity of ash in general approaches pretty closely to five per cent. Still more diversified results are obtained from the entire plants; but this diversity is probably much more apparent than real, and must be, in part at least, dependent on the proportion existing between the stem and leaves, for the leaves are peculiarly rich in ash, and a leafy plant must necessarily yield a higher total percentage of ash, although, if stems and leaves were separately examined, they might not show so conspicuous a difference.

The leaves surpass all other parts of plants, in the proportion of inorganic constituents they contain, the table showing that in some instances, as in the maple and Jerusalem artichoke, they exceed one-fourth of the whole weight of the dry matter. In other leaves, and more especially in those of the coniferae, the proportion is much smaller. Taking the average of all the analyses hitherto made, it appears that leaves contain about thirteen per cent of ash, but the variations on either side are so large that little value is to be attached to it except as an indication of the general abundance of mineral matters.

In roots and tubers the variations are less, and all, except the potato and the turnip, contain about seven per cent of ash.

The smallest proportion of mineral matter is found in wood. In one case only does the proportion reach five per cent, while the average scarcely exceeds one, and in the fir the quantity amounts to no more than one six-hundredth of the dry matter. In the bark the quantity is much larger, and may be stated at seven per cent.

The general proportion of ash found in different parts of plants is given in round numbers in the subjoined table:—

Wood 1 Seeds 3 Stems and straws 5 Roots and tubers 7 Bark 7 Leaves 13

The differences in the quantity of ash contained in different parts of plants are obviously intended to serve a useful purpose, and it is interesting to observe that the wood which is destined to remain for a long period, sometimes for several centuries, a part of the plant, contains the smallest proportion, and it is not improbable that what it does contain is really due, not to the actual woody matter itself, but to the sap which permeates its vessels. By this arrangement but a small proportion of these important mineral matters, which the soil supplies in very limited quantity, is locked up within the plant, and those which are absorbed, after circulating through it, and fulfilling their allotted functions, are accumulated in the leaves, and annually returned to the soil.

The different proportions of mineral matters contained in the individual organs of plants is most strikingly illustrated when parallel experiments are made on the same species; but the number of instances in which a sufficiently extensive series of analyses has been made to show this, is comparatively limited, and is confined to the oat, the orange-tree, and the horse chesnut—each of which has formed the subject of a very elaborate investigation. The following table gives the results obtained on the oat:—

- - - - - - Hopetoun Hopetoun Potato Black Sandy Oats, Oats, Oats, Oats, Oats, Mean. North- Fife- North- Edin- Fife- umberland. shire. umberland. burgh. shire. - - - - - - Grain 2.14 1.81 2.22 2.11 1.76 2.00 Husk 6.47 6.03 6.99 8.24 6.03 6.75 Chaff 16.53 17.23 15.59 19.19 18.97 16.06 Leaves 8.44 7.19 14.59 10.29 15.92 10.88 Upper part of straw 4.95 5.44 9.22 8.25 11.0 7.77 Middle part of straw 6.11 5.23 7.41 6.53 9.01 6.66 Lower part of straw 5.33 5.18 9.76 7.11 7.30 6.93 - - - - - -

The specimens of oats on which these analyses were made were from different districts of country, grown on soils of different quality, and were, further, of different varieties; and yet they show, on the whole, a remarkable similarity in the proportion of ash in each part, and indicate that there is a normal quantity belonging to it. Such a series of analyses also affords the most convincing proof that the inorganic matters cannot be fortuitous, and merely absorbed from the soil along with their organic food, as the old chemists supposed, because, in that case, they ought to be uniformly distributed throughout the entire plant, and not accumulated in particular proportions in each individual organ.

Not only does the proportion of ash vary in the different parts of a plant, but even in the same part it is greatly influenced by its period of growth. The laws which regulate these variations are very imperfectly known, but in general it is observed that during the period of active growth the quantity of ash is largest. Thus, it has been found that in early spring the wood of the young shoots of the horse-chesnut contains 9.9 per cent of ash. In autumn this has diminished to 3.4, and the last year's twigs contain only 1.1 per cent, while in the old wood the quantity does not exceed 0.5. Saussure has also observed that the quantity of ash diminishes in certain plants when the seed has ripened. Thus, he found that the percentages of ash, before flowering, and after seeding, were as follows:—

Before flowering. With ripe seed. Sunflower 14.7 9.3 Wheat 7.9 3.3 Maize 12.2 4.6

On the other hand, the quantity of ash in the leaves of trees increases considerably in autumn, as shown by this table:—

PER-CENTAGE OF ASH IN May. September. Oak leaves 5.3 5.5 Poplar 6.6 9.3 Hazel 6.1 7.0 Horse-chesnut 7.2 8.6

In general, the proportion of ash appears to increase as the plant reaches maturity, and this is particularly seen in the oat, of which very complete analyses have been made at different periods of its growth:—

Proportion of Ash in different parts of the Oat at different periods of its growth.

- - Grain Date. Stalks. Leaves. Chaff. with husk. - - 2d July 7.83 11.35 ... 4.91 9th July 7.80 12.20 ... 4.36 16th July 7.94 12.61 6.00 3.38 23d July 7.99 16.45 9.11 3.62 30th July 7.45 16.44 12.28 4.22 5th August 7.63 16.05 13.75 4.31 13th August 6.62 20.47 18.68 4.07 20th August 6.66 21.14 21.07 3.64 27th August 7.71 22.13 22.46 3.51 3d September 8.35 20.90 27.47 3.65 - -

The increase is here principally confined to the leaves and chaff, while the stalks, which owe their strength to a considerable extent to the inorganic matters they contain, are equally supplied at all periods of their growth. In the grain only is there a diminution, but this is apparent and not real, and is due to the fact that the determination of the quantity of ash, as made on the grain with its husk, and the former, which contains only a small quantity of mineral matters, increases much more rapidly in weight than the latter, when it approaches the period of ripening, and it is accordingly during the last three weeks of its growth that this diminution becomes apparent.

The nature of the soil has also a very important influence on the proportion of mineral matters, and of this an interesting illustration is given in the following table, which shows the quantities found in the grain and straw of the same variety of the pea grown on fourteen different soils:—

- Seed. Straw. - 1 2.30 2 3.25 3.43 3 4.27 3.62 4 3.40 3.39 5 2.99 3.90 6 3.19 6.80 7 2.53 3.90 8 2.27 6.59 9 2.69 3.49 10 1.61 3.91 11 3.11 5.28 12 3.34 7.57 13 2.78 3.76 14 3.01 3.38 -

Although those differences are very large, especially in the straw, and must be attributed to the soil, it has hitherto been found impossible to ascertain the nature of the relation subsisting between it and the crops it yields; indeed, it must obviously be dependent on very complicated questions, which cannot at present be solved, for it may be observed that the increase in the grain does not occur simultaneously with that in the straw, and in several cases a large proportion of ash in the former is associated with an unusually small amount in the latter. A priori, it might be expected that those soils which are especially rich in the more important constituents of the ash should yield a produce containing more than the average quantity, but this is very far from being an invariable occurrence, and not unfrequently the very reverse is the case. In some instances the variations may be traced to the soil, as in the following analyses of the fruit of the horse-chesnut, grown on an ordinary forest soil, and on a rich soil, produced by the disintegration of porphyritic rock, in which the latter yields a much larger quantity of ash:—

Kernel of seed. Green husk. Brown husk. Forest soil 2.26 4.53 1.70 Porphyry soil 3.36 7.29 2.20

In the majority of instances we fail to establish any connection between the nature of the soil and the plants it yields, chiefly because we are still very deficient in analyses of those grown on uncultivated soils; and on cultivated land it is impossible to draw conclusions, because the nature of the manure exerts an influence quite as great, if not greater, than that of the soil itself.

The relative proportion in which the different mineral matters enter into the composition of the ash varies within very wide limits, as will be apparent from the following table, containing a selection of the best analyses of our common cultivated and a few uncultivated plants.

Table of the Composition of the Ash of different Plants in 100 Parts.

Note.—Alumina and oxide of manganese occur so rarely, that separate columns have not been introduced for them, but their quantity is stated in notes at the end of the table.

- - - Potash. Soda. Chloride Chloride Lime. Magnesia. of of Potassium. Sodium. - - - Wheat, grain 30.02 3.82 ... ... 1.15 13.39 straw 17.98 2.47 ... ... 7.42 1.94 chaff 9.14 1.79 ... ... 1.88 1.27 Barley, grain 21.14 ... 5.65 1.01 1.65 7.26 straw 11.22 ... ... 2.14 5.79 2.70 Oats, grain[B] 20.63 ... 1.03 ... 10.28 7.82 straw 19.46 1.93 2.71 4.27 7.01 3.79 chaff[C] 6.33 3.93 ... 0.24 1.95 0.38 Rye, grain 33.83 0.39 ... ... 2.61 12.81 straw 17.20 ... 0.30 0.60 9.10 2.40 Maize, grain 28.37 1.74 ... trace 0.57 13.60 stalks and leaves 35.26 ... ... 2.29 10.53 5.52 Rice, grain 20.21 2.49 ... ... 7.18 4.26 Buckwheat, straw 31.71 ... 7.42 4.55 15.71 1.66 Peas (gray), seed 41.70 ... 3.82 1.24 4.78 5.78 straw 21.30 4.22 ... ... 37.17 7.17 Beans (common field), grain 51.72 0.54 ... ... 5.20 6.90 straw 32.85 2.77 ... 11.54 19.85 2.53 Tare, straw 32.82 ... 3.27 4.03 20.78 5.31 straw 31.72 ... 7.41 4.55 15.71 1.66 - - -

+ -+ -+ + -+ + -+ Oxide Phosphoric Sulphuric Carbonic Silica. of Acid. Acid. Acid. Iron. + -+ -+ + -+ + -+ Wheat, grain 0.91 46.79 ... ... 3.89 straw 0.45 2.75 3.09 ... 63.89 chaff 0.37 4.31 ... ... 81.22 Barley, grain 2.13 28.53 1.91 ... 30.68 straw 1.36 7.20 1.09 ... 68.50 Oats, grain 3.85 50.44 ... ... 4.40 straw 1.49 5.07 3.35 1.36 49.56 chaff 1.58 1.04 9.61 ... 72.85 Rye, grain 1.04 39.92 0.17 ... 9.22 straw 1.40 3.80 0.80 ... 64.50 Maize, grain 0.47 53.69 ... ... 1.55 stalks and leaves 2.28 8.09 5.16 2.87 27.98 Rice, grain 2.12 62.23 ... ... 1.37 Buckwheat, straw ... 10.34 4.67 20.37 3.57 Peas (gray), seed 0.18 36.50 4.47 0.82 0.68 straw 1.07 4.65 8.68 12.48 3.23 Beans (common field), grain ... 28.72 3.05 3.42 0.42 straw 0.61 0.49 1.40 25.32 2.61 Tare, straw 0.65 10.59 2.52 18.73 1.28 straw ... 10.34 4.67 20.37 3.57 + -+ -+ + -+ + -+

- - - Potash. Soda. Chloride Chloride Lime. Magnesia. of of Potassium. Sodium. - - - Flax, seed 34.17 1.69 ... 0.36 8.40 13.11 straw 21.53 3.68 ... 9.21 21.20 4.20 Rape, seed[D] 16.33 0.34 ... 0.96 8.30 8.80 straw[E] 16.63 10.57 ... 2.53 21.51 2.92 Spurry 26.12 1.14 ... 8.90 14.46 8.88 Chicory root 34.64 ... 8.92 2.98 ... ... Red clover 25.60 ... 9.08 6.02 21.57 8.47 Cow grass, Trifolium medium 22.78 ... 12.39 1.86 24.42 8.86 Yellow clover 27.48 ... 11.72 8.16 17.26 8.39 Alsike clover 29.72 ... 6.29 1.05 26.83 4.01 Lucerne 27.56 ... 11.64 1.91 20.60 5.22 Anthoxanthum odoratum 32.03 ... 7.03 4.90 9.21 2.53 Alopecurus pratensis 37.03 ... 9.50 ... 3.90 1.28 Avena pubescens 31.21 ... 4.05 5.66 4.72 3.17 Bromus erectus 20.33 ... 10.63 1.38 10.38 4.99 Bromus mollis 30.09 0.33 ... 3.11 6.64 2.60 Cynosurus cristatus 24.99 ... 11.60 ... 10.16 2.43 Dactylis glomerata 29.52 ... 17.86 3.09 5.82 2.22 Festuca duriuscula 31.84 ... 8.17 0.62 10.31 2.83 Holcus lanatus 34.83 ... 3.91 6.66 8.31 3.41 Lolium perenne 24.67 ... 13.80 7.25 9.64 2.85 Annual ryegrass 28.99 0.87 ... 5.11 6.82 2.59 Poa annua 41.86 ... 0.47 3.35 11.69 2.44 Poa pratensis 31.17 ... 11.25 1.31 5.63 2.71 Poa trivialis 29.40 ... 6.90 ... 8.80 3.22 Phleum pratense 31.09 ... 0.70 3.24 14.94 5.30 Plantago lanceolata 33.26 ... 4.53 8.80 19.01 3.51 Poterium Sanguisorba 30.26 ... 3.27 1.35 24.82 4.21 Achillea Millefolia 30.37 ... 20.49 3.63 13.40 3.01 Potato, tuber 43.18 0.09 ... 7.92 1.80 3.17 stem 39.53 3.95 ... 20.43 14.85 4.10 leaves 17.27 ... 4.95 11.37 27.69 7.78 Jerusalem Artichoke 55.89 ... 4.88 ... 3.34 1.30 stem 38.40 0.69 ... 4.68 20.31 1.91 leaves 6.81 3.72 ... 1.82 40.15 1.95 Turnip, seed 21.91 1.23 ... ... 17.40 8.74 bulb 23.70 14.75 ... 7.05 11.82 3.28 leaves 11.56 12.43 ... 12.41 28.49 2.62 Mangold Wurzel, root 21.68 3.13 ... 49.51 1.90 1.79 leaves 8.34 12.21 ... 37.66 8.72 9.84 Carrot, root 42.73 12.11 ... ... 5.64 2.29 leaves 17.10 4.85 ... 3.62 24.05 0.89 Kohl-rabi, bulb 36.27 2.84 ... 11.90 10.20 2.36 leaves 9.31 ... 5.99 6.66 30.31 3.62 Cow cabbage, head 40.86 2.43 ... ... 15.01 2.39 stalk 40.93 4.05 ... 2.08 10.61 3.85 Poppy seed 9.10 ... 7.15 1.94 35.36 9.49 leaves 36.37 ... 2.50 2.51 30.24 6.47 Mustard seed (white) 25.78 0.33 ... ... 19.10 5.90 Radish root 21.16 ... 1.29 7.07 8.78 3.53 Tobacco leaves 36.37 ... 2.50 2.51 30.24 6.47 Fucus nodosus[F] 20.03 4.58 ... 24.33 9.60 6.65 Fucus vesiculosus[G] 20.75 6.09 ... 24.81 8.92 5.83 Laminaria digitata[H] 12.16 ... 2.30 19.34 4.62 10.94 - - -

+ -+ -+ + -+ + -+ Oxide Phosphoric Sulphuric Carbonic Silica. of Acid. Acid. Acid. Iron. + -+ -+ + -+ + -+ Flax, seed 0.50 38.54 1.56 0.22 1.45 straw 5.58 7.53 3.39 15.75 7.92 Rape, seed 1.79 31.90 5.38 5.44 19.98 straw 1.30 4.68 3.90 23.04 11.80 Spurry ... 10.20 1.79 27.38 1.14 Chicory root ... ... ... ... ... Red clover 1.26 4.09 2.96 18.05 1.95 Cow grass, Trifolium medium 1.09 4.94 2.66 20.16 1.12 Yellow clover 1.40 ... 4.82 4.31 1.76 Alsike clover 0.71 5.64 3.25 20.74 1.73 Lucerne 2.23 6.47 4.80 15.94 2.63 Anthoxanthum odoratum 1.18 10.09 3.39 1.26 28.35 Alopecurus pratensis 0.47 6.25 2.16 0.65 38.75 Avena pubescens 0.72 10.82 3.37 ... 36.28 Bromus erectus 0.26 7.53 5.46 0.55 38.48 Bromus mollis 0.28 9.62 4.91 9.07 33.34 Cynosurus cristatus 0.18 7.24 3.20 ... 40.11 Dactylis glomerata 0.59 8.60 3.52 2.09 26.65 Festuca duriuscula 0.78 12.07 3.45 1.38 28.53 Holcus lanatus 0.31 8.02 4.41 1.82 28.31 Lolium perenne 0.21 8.73 5.20 0.49 27.13 Annual ryegrass 0.28 10.07 3.45 ... 41.79 Poa annua 1.57 9.11 10.18 3.29 16.03 Poa pratensis 0.28 10.02 4.26 0.40 32.93 Poa trivialis 0.29 9.13 4.47 0.29 37.50 Phleum pratense 0.27 11.29 4.86 4.02 31.09 Plantago lanceolata 0.90 7.08 6.11 14.40 2.37 Poterium Sanguisorba 0.86 7.81 4.84 21.72 0.83 Achillea Millefolia 0.21 7.13 2.44 9.36 9.92 Potato, tuber 0.44 8.61 15.24 18.29 1.94 stem 1.34 6.68 6.56 ... 2.56 leaves 4.50 13.60 6.37 ... 6.47 Jerusalem Artichoke 0.45 16.99 3.77 11.80 1.52 stem 0.88 2.97 3.23 25.40 1.51 leaves 1.14 6.61 2.21 24.31 17.25 Turnip, seed 1.95 40.17 7.10 0.82 0.67 bulb 0.47 9.31 16.13 10.74 2.69 leaves 3.02 4.85 10.36 6.18 8.04 Mangold Wurzel, root 0.52 1.65 3.14 15.23 1.40 leaves 1.46 5.89 6.54 6.92 2.35 Carrot, root 0.51 12.31 4.26 18.00 1.11 leaves 3.43 6.21 5.08 23.15 11.61 Kohl-rabi, bulb 0.38 13.45 11.43 10.24 0.83 leaves 5.50 9.43 10.63 8.97 9.57 Cow cabbage, head 0.77 12.53 7.27 16.68 1.66 stalk 0.41 19.57 11.11 6.33 1.04 Poppy seed 0.41 31.38 1.92 ... 3.24 leaves 2.14 3.28 5.09 ... 11.40 Mustard seed (white) 0.39 44.97 2.19 ... 1.31 Radish root 1.19 41.09 7.71 ... 8.17 Tobacco leaves 2.18 3.24 5.09 ... 11.40 Fucus nodosus 0.26 1.71 21.97 6.39 0.38 Fucus vesiculosus 0.35 2.14 28.01 2.20 0.67 Laminaria digitata 0.45 1.75 7.26 15.23 1.20 + -+ -+ + -+ + -+

A simple inspection of this table leads to various interesting conclusions. It is particularly to be observed that some of the constituents of the ash are not invariably present, and two at least—namely, alumina and manganese—are found so rarely as to justify the inference that they are not indispensable. Of the other substances, iodine is restricted exclusively to sea-plants, but to them it appears to be essential. Oxide of iron, which occurs only in small quantities, has sometimes been considered fortuitous, but it is almost invariably present, and the experiments of Prince Salm Horstmar leave no doubt that it is essential to the plant. Its function is unknown, but it is an important constituent of the blood of herbivorous animals, and may be present in the plant, less for its own benefit than for that of the animal of which it is destined to become the food.

Soda appears to be a comparatively unimportant constituent of the ash, of which it generally forms but a small proportion, although the instances of its entire absence are rare. In the cruciferous plants (turnip, rape, etc.) it is found abundantly, and to them it appears indispensable, but in most other plants it admits of replacement by potash. It seems probable that where the soil is rich in the latter substance, plants will select that alkali in preference to soda; but as they must have a certain quantity of alkali, the latter may supply the place of the former where it is deficient. Cultivation, probably by enriching the soil in that element, increases the proportion of potash found in the ash of plants, as is remarkably seen in the asparagus, which gave the following quantities of alkalies and chlorine:—

Wild. Cultivated. Potash 18.8 50.5 Soda 16.2 trace. Chlorine 16.5 8.3

The soda having almost entirely disappeared in the cultivated plant, while a corresponding increase had taken place in the quantity of potash.

Potash is one of the most important elements of the ash of all plants, rarely forming less than 20, and sometimes more than 50 per cent of its weight. The latter proportion occurs chiefly in the roots and tubers, but it is also abundant in all seeds and in the grasses. The straw, and particularly the chaff of the cereals, and the leaves of most plants, contain it in smaller quantity, although exceptions to this are not unfrequent, one of the most curious being the case of poppy-seed, which contains only about 12 per cent, while the leaves yield upwards of 37 per cent.

The proportion of lime varies within very wide limits, being sometimes as low as 1, and in other plants reaching 40 per cent of their ash. The former proportion occurs in the grains of the cerealia, and the latter in the leaves of some plants, and more especially in the Jerusalem artichoke. The turnip and some of the leguminous plants also contain it abundantly.

Magnesia is generally found in small quantity. It is largest in the grains, amounting in them to about 12 or 13 per cent of the ash, but in other plants it varies from 2 to 4 per cent. Although small in quantity, it is an important substance, and apparently cannot be dispensed with; at least there is no instance known of its entire absence.

Chlorine is by no means an invariable constituent of the ash, although it is generally present, and sometimes in considerable quantity. It is most abundant when the proportion of soda is large, and exists in the ash principally in combination with that base as common salt. The relation between these two elements may be traced more or less distinctly throughout the whole table of analyses, and conspicuously in that of mangold-wurzel, where the common salt amounts to almost exactly one-half of the whole mineral matter. The analyses of the cultivated and uncultivated asparagus also show that a diminution in the soda is accompanied by a reduction in the proportion of chlorine.

Sulphuric Acid is an essential constituent of the ash. But it is to be observed that it is in some instances entirely, and in all partially, a product of the combustion to which the plant has been submitted in order to obtain the ash. It is partly derived from the sulphur contained in the albuminous compounds, which is oxidised and converted into sulphuric acid during the process of burning the organic matter, and remains in the ash. The quantity of sulphuric acid found in the ash is, however, no criterion of that existing in the plant, for a considerable quantity of it escapes during burning. The extent to which this occurs in particular instances is well illustrated by reference to the case of white mustard, which yields an ash containing only 2.19 of sulphuric acid, equivalent to 0.9 of sulphur; and if calculated on the seed itself, this will amount to no more than 0.039 per cent, while experiments made in another manner prove it to contain about thirty times as much, or more than 1 per cent. For the purpose of determining the total quantity of sulphur which the plants contain in their natural state, it is necessary to oxidise them by means of nitric acid; and from such experiments the following table, showing the total amount of sulphur contained in 100 parts of different plants, dried at 212 deg., has been constructed:—

Poa palustris 0.165 Lolium perenne 0.310 Italian Ryegrass 0.329 Trifolium pratense 0.107 repens 0.099 Lucerne 0.336 Vetch 0.178 Potato tuber 0.082 tops 0.206 Carrot, root 0.092 tops 0.745 Mangold-Wurzel, root 0.058 tops 0.502 Swede, root 0.435 tops 0.458 Rape 0.448

Drumhead Cabbage 0.431 Wheat, grain 0.068 straw 0.245 Barley, grain, 0.053 straw 0.191 Oats, grain 0.103 straw 0.289 Rye, grain 0.051 Beans 0.056 Peas 0.127 Lentils 0.110 Hops 1.063 Gold of Pleasure 0.253 Black Mustard 1.170 White Mustard 1.050

Phosphoric acid, which may be looked upon as the most important mineral constituent of plants, is found to be present in very variable proportions. The straws, stems, and leaves contain it in comparatively small quantity, but in the seeds of all plants it is very abundant. In these of the cereals it constitutes nearly half of their whole mineral components, and it rarely falls below 30 per cent.

Carbonic acid occurs in very variable quantities in the ash. It is of comparatively little importance in itself, and is really produced by the oxidation of part of the carbonaceous matters of the plant; but it has a special interest, in so far as it shows that part of the bases contained in the plant must in its natural state have been in union with organic acids, or combined in some way with the organic constituents of the plant.

Silica is an invariable constituent of the ash, but in most plants occurs but in small quantity. The cereals and grasses form an exception to this rule, for in them it is an abundant and important element. It is not, however, uniformly distributed through them, but is accumulated to a large extent in the stem, to the strength and rigidity of which it greatly contributes. The hard shining layer which coats the exterior of straw, and which is still more remarkably seen on the surface of the bamboo, consists chiefly of silica; and in the latter plant this element is sometimes so largely accumulated, that concretions resembling opal, and composed entirely of it, are found loose within its joints. The necessity for a large supply of silica in the stems of other plants does not exist, and in them it rarely exceeds 5 or 6 per cent, but in some leaves it is more abundant.

A knowledge of the composition of the ash of plants is of considerable importance in a practical point of view, and enables us in many instances to explain why some plants will not grow upon particular soils on which others flourish. Thus, for instance, a plant which contains a large quantity of lime, such as the bean or turnip, will not grow in a soil in which that element is deficient, although wheat or barley, which require but little lime, may yield excellent crops. Again, if the soil be deficient in phosphoric acid, those plants only will grow luxuriantly which require but a small quantity of that element, and hence it follows that on such a soil plants cultivated for the sake of their stems, roots, or leaves, in which the quantity of phosphoric acid is small, may yield a good return; while others, cultivated for the sake of their seed, in which the great proportion of that constituent of the ash is accumulated, may yield a very small crop. It is obvious also that even where a soil contains a proper quantity of all its ingredients, the repeated cultivation of a plant which removes a large quantity of any individual element, may, in the course of time, so far reduce the amount of that substance as to render the soil incapable of any longer producing that plant, although, if it be replaced by another which requires but little of the element thus removed, it may again produce an abundant crop. On this principle also, attempts have been made to explain the rotation of crops, which has been supposed to depend on the cultivation in successive years of plants which abstract from the soil preponderating quantities of different mineral matters. But though this has unquestionably a certain influence, we shall afterwards see reason to doubt whether it affords a sufficient explanation of all the observed phenomena.

It may be observed, on examining the table of the percentage and position of the ash, that some plants are especially rich in alkalies, while in others lime or silica preponderate, and it would therefore be the object of the farmer to employ, in succession, crops containing these elements in different proportions. In carrying out this view, attempts have been made to classify different plants under the heads of silica plants, lime plants, and potash plants; and the following table, extracted from Liebig's Agricultural Chemistry, in which the constituents of the ash are grouped under the three heads of salts of potash and soda, lime and magnesia, and silica, gives such a classification as far as it is at present possible:—

Salts of Salts of Silica. Potash and Lime and Soda. Magnesia. - - Silica { Oat straw with seeds 34.00 4.00 62.00 Plants. { Wheat straw 22.50 7.20 61.50 { Barley straw with seeds 19.00 25.70 55.30 { Rye straw 18.65 16.52 63.89 { Good hay 6.00 34.00 60.00 Lime { Tobacco 24.34 67.44 8.30 Plants { Pea straw 27.82 63.74 7.81 { Potato plant 4.20 59.40 36.40 { Meadow Clover 39.20 56.00 4.90 Potash { Maize straw 72.45 6.50 18.00 Plants. { Turnips 81.60 18.40 { Beet root 88.00 12.00 { Potatoes 85.81 14.19 { Jerusalem Artichoke 84.30 15.70

The special application of these facts must be reserved till we come to treat of the rotation of crops.

It is manifest that, as the crops removed from the soil all contain a greater or less amount of inorganic matters, they must be continually undergoing diminution, and at length be completely exhausted unless their quantity is maintained from some external source. In many cases the supply of these substances is so large that ages may elapse before this becomes apparent, but where the quantity is small, a system of reckless cropping may reduce a soil to a state of absolute sterility. A remarkable illustration of this fact is found in the virgin soils of America, from which the early settlers reaped almost unheard-of crops, but, by injudicious cultivation, they were soon exhausted and abandoned, new tracts being brought in and cultivated only to be in their turn abandoned. The knowledge of the composition of the ash of plants assists us in ascertaining how this exhaustion may be avoided, and indicates the mode in which such soils may be preserved in a fertile state.

FOOTNOTES:

[Footnote A: Apparently a species of Sinapis.]

[Footnote B: Oxide of Manganese, 0.42.]

[Footnote C: Oxide of Manganese, 0.92.]

[Footnote D: Alumina, 1.02.]

[Footnote E: Alumina, 0.63.]

[Footnote F: Iodide of Potassium, 0.44; Sulphuret of Sodium, 3.66.]

[Footnote G: Iodide of Potassium, 0.23.]

[Footnote H: Iodide of Potassium, 1.68.]



CHAPTER V.

THE SOIL—ITS CHEMICAL AND PHYSICAL CHARACTERS.

No department of agricultural chemistry is surrounded with greater difficulties and uncertainties than that relating to the properties of the soil. When chemistry began to be applied to agriculture, it was not unnaturally supposed that the examination of the soil would enable us to ascertain with certainty the mode in which it might be most advantageously improved and cultivated, and when, as occasionally happened, analysis revealed the absence of one or more of the essential constituents of the plant in a barren soil, it indicated at once the cause and the cure of the defect. But the expectations naturally formed from the facts then observed have been as yet very partially fulfilled; for, as our knowledge has advanced, it has become apparent that it is only in rare instances that it is possible satisfactorily to connect together the composition and the properties of a soil, and with each advancement in the accuracy and minuteness of our analysis the difficulties have been rather increased than diminished. Although it is occasionally possible to predicate from its composition that a particular soil will be incapable of supporting vegetation, it not unfrequently happens that a fruitful and a barren soil are so similar that it is impossible to distinguish them from one another, and cases even occur in which the barren appears superior to the fertile soil. The cause of this apparently anomalous phenomenon lies in the fact that analysis, however minute, is unable to disclose all the conditions of fertility, and that it must be supplemented by an examination of its physical and other chemical properties, which are not indicated by ordinary experiments. Of late years very considerable progress has been made in the investigation of the properties of the soil, and many facts of great importance have been discovered, but we are still unable to assert that all the conditions of fertility are yet known, and the practical application of those recently discovered is still very imperfectly understood.

It must not be supposed that a careful analysis of a soil is without value, for very important practical deductions may often be drawn from it, and when this is not practicable it is not unfrequently due to its being imperfect or incomplete, for it is so complex that the cases in which all the necessary details have been eliminated are even now by no means numerous. In fact, the want of a large number of thorough analyses of soils of different kinds is a matter of some difficulty, and so soon as a satisfactory mode of investigation can be determined upon, a full examination of this subject would be of much importance.

Origin of Soils.—The constituents of the soil, like those of the plant, may be divided into the great classes of organic and inorganic. The origin of the former has been already discussed: they are derived from the decay of plants which have already grown upon the soil, and which, in various stages of decomposition, form the numerous class of substances grouped together under the name of humus. The organic substances may therefore be considered as in a manner secondary constituents of the soil, which have been accumulated in it as the consequence of the growth and decay of successive generations of plants, while the primeval soil consisted of inorganic substances only.

The inorganic constituents of the soil are obtained as the result of a succession of chemical changes going on in the rocks which protrude through the surface of the earth. We have only to examine one of these rocks to observe that it is constantly undergoing a series of important changes. Under the influence of air and moisture, aided by the powerful agency of frost, it is seen to become soft, and gradually to disintegrate, until it is finally converted into an uniform powder, in which the structure of the original rock is with difficulty, if at all distinguishable. The rapidity with which these changes take place is very variable; in the harder rocks, such as granite and mica slate it is so slow as to be scarcely perceptible, while in others, such as the shales of the coal formation, a very few years' exposure is sufficient for the purpose. These actions, operating through a long series of years, are the source of the inorganic constituents of all soils.

Geology points to a period at which the earth's surface must have been altogether devoid of soil, and have consisted entirely of hard crystalline rocks, such as granite and trap, by the disintegration of which, slowly proceeding from the creation down to the present time, all the soils which now cover the surface have been formed. But they have been produced by a succession of very complicated processes; for these disintegrated rocks being washed away in the form of fine mud, or at least of minute particles, and being deposited at the bottom of the primeval seas, have there hardened into what are called sedimentary rocks, which being raised above the surface by volcanic action or other great geological forces, have been again disintegrated to yield different soils. Thus, then, all soils are directly or indirectly derived from the crystalline rocks, those overlying them being formed immediately by their decomposition, while those found above the sedimentary rocks may be traced back through them to the crystalline rocks from which they were originally formed.

Such being the case, the composition of different soils must manifestly depend on that of the crystalline rocks from which they have been derived. Their number is by no means large, and they all consist of mixtures in variable proportions of quartz, felspar, mica, hornblende, augite, and zeolites. With the exception of quartz and augite, these names are, however, representatives of different classes of minerals. There are, for instance, several different minerals commonly classified under the name of felspar, which have been distinguished by mineralogists by the names of orthoclase, albite, oligoclase, and labradorite; and there are at least two sorts of mica, two of hornblende, and many varieties of zeolites.

Quartz consists of pure silica, and when in large masses is one of the most indestructible rocks. It occurs, however, intermixed with other minerals in small crystals, or irregular fragments, and forms the entire mass of pure sand.

The four kinds of felspar which have been already named are compounds of silica with alumina, and another base which is either potash, soda, or lime. Their composition is as follows, two examples of each being given—

Orthoclase. Albite. Oligoclase. Labradorite. - - Silica 65.72 65.00 67.99 68.23 62.70 63.51 54.66 54.67 Alumina 18.57 18.64 19.61 18.30 23.80 23.09 27.87 27.89 Peroxide of iron traces 0.83 0.70 1.01 0.62 0.31 Oxide of manganese traces 0.13 Lime 0.34 1.23 0.66 1.26 4.60 2.44 12.01 10.60 Magnesia 0.10 1.03 0.51 0.02 0.77 0.18 Potash 14.02 9.12 2.53 1.05 2.19 0.49 Soda 1.25 3.49 11.12 7.99 8.00 9.37 5.46 5.05 100.00 99.47 100.08 99.83 100.79 101.37 100.00 99.19 -

It is obvious that soils produced by the disintegration of these minerals must differ materially in quality. Those yielded by orthoclase must generally abound in potash, while albite and labradorite, containing little or none of that element, must produce soils in which it is deficient. The quality of the soil they yield is not however entirely dependent on the nature of the particular felspar which yields it, but is also intimately connected with the extent to which the decomposition has advanced. It is observed that different felspars undergo decomposition with different degrees of rapidity but after a certain time they all begin to lose their peculiar lustre, acquire a dull and earthy appearance, and at length fall into a more or less white and soft powder. During this change water is absorbed, and, by the decomposing action of the air, the alkaline silicate is gradually rendered soluble, and at length entirely washed away, leaving a substance which, when mixed with water, becomes plastic, and has all the characters of common clay. The nature of this change will be best seen by the following analysis of the clay produced during this composition, which is employed in the manufacture of porcelain under the name of kaolin, or china clay—

Silica 46.80 Alumina 36.83 Peroxide of iron 3.11 Carbonate of lime 0.55 Potash 0.27 Water 12.44 —— 100.00

In this instance the decomposition of the felspar had reached its limit, a mere trace of potash being left, but if taken at different stages of the process, variable proportions of that alkali are met with. This decomposition of felspar is the source of the great deposits of clay which are so abundantly distributed over the globe, and it takes place with nearly equal rapidity with potash and soda felspar. It is rarely complete, and the soils produced from it frequently contain a considerable proportion of the undecomposed mineral, which continues for a long period to yield a supply of alkalies to the plants which grow on them.

Mica is a very widely distributed mineral, and two varieties of it are distinguished by mineralogists, one of which is characterised by the large quantity of magnesia it contains. Different specimens are found to vary very greatly in composition, but the following analyses may represent their most usual composition:

MICA. Potash. Magnesia. Silica 46.36 42.65 Alumina 36.80 12.96 Peroxide of iron 4.53 - Protoxide of iron - 7.11 Oxide of manganese 0.02 1.06 Magnesia - 25.75 Potash 9.22 6.03 Hydrofluoric acid 0.70 0.62 Water 1.84 3.17 99.47 99.35

Mica undergoes decomposition with extreme slowness, as is at once illustrated by the fact that its shining scales may frequently be met with entirely unchanged in the soil. Its persistence is dependent on the small quantity of alkaline constituents which it contains; and for this reason it is observed that the magnesian micas undergo decomposition less rapidly than those containing the larger quantity of potash. Eventually, however, both varieties become converted into clay, their magnesia and potash passing gradually into soluble forms.

Hornblende and augite are two widely distributed minerals, which are so similar in composition and properties that they may be considered together. Of the former two varieties, basaltic and common have been distinguished, and their composition is given below:—

Hornblende. Common. Basaltic. Augite.

Silica 41.50 42.24 50.12 Alumina 15.75 13.92 4.20 Protoxide of iron 7.75 14.59 11.60 Oxide of manganese 0.25 0.33 — Lime 14.09 12.24 20.55 Magnesia 19.40 13.74 13.70 Water 0.50 — — —— —— —— 99.24 97.05 99.67

In these minerals alkalies are entirely absent, and their decomposition is due to the presence of protoxide of iron, which readily absorbs oxygen from the air, when the magnesia is separated and a ferruginous clay left.

The minerals just referred to, constitute the great bulk of the mountain masses, but they are associated with many others which take part in the formation of the soil. Of these the most important are the zeolites which do not occur in large masses but are disseminated through the other rocks in small quantity. They form a large class of minerals of which Thomsonite and natrolite may be selected as examples—

Thomsonite. Natrolite.

Silica 38.73 48.68 Alumina 30.84 26.36 Lime 13.43 — Potash 0.54 0.23 Soda 3.85 16.00 Water 13.09 9.55 —— —— 100.48 100.83

They are chiefly characterized by containing their silica in a soluble state, and hence may yield that substance to the plants in a condition particularly favourable for absorption.

It is obvious from what has been stated that all these minerals are capable, by their decomposition, of yielding soft porous masses having the physical properties of soils, but most of them would be devoid of many essential ingredients, while not one of them would yield either phosphoric acid, sulphuric acid, or chlorine. It has, however, been recently ascertained that certain of these minerals, or at least the rocks formed from them, contain minute, but distinctly appreciable traces of phosphoric acid, although in too small quantity to be detected by ordinary analysis; and small quantities of chlorine and sulphuric acid may also in most instances be found.

Still it will be observed that most of these minerals would yield a soil containing only two or three of those substances, which, as we have already learned, are essential to the plant. Thus, potash felspar, while it would give abundance of potash, would be but an inefficient source of lime and magnesia; and labradorite, which contains abundance of lime, is altogether deficient in magnesia and potash.

Nature has, however, provided against this difficulty, for she has so arranged it that these minerals rarely occur alone, the rocks which form our great mountain masses being composed of intimate mixtures of two or more of them, and that in such a manner that the deficiencies of the one compensate those of the other. We shall shortly mention the composition of these rocks.

Granite is a mixture of quartz, felspar, and mica in variable proportions, and the quality of the soil it yields depends on whether the variety of felspar present be orthoclase or albite. When the former is the constituent, granite yields soils of tolerable fertility, provided their climatic conditions be favourable; but it frequently occurs in high and exposed situations which are unfavourable to the growth of plants. Gneiss is a similar mixture, but characterised by the predominance of mica, and by its banded structure. Owing to the small quantity of felspar which it contains, and the abundance of the difficulty decomposable mica, the soils formed by its disintegration are generally inferior. Mica slate is also a mixture of quartz, felspar, and mica, but consisting almost entirely of the latter ingredient, and consequently presenting an extreme infertility. The position of the granite, gneiss, and mica slate soils in this country is such that very few of them are of much value; but in warm climates they not unfrequently produce abundant crops of grain. Syenite is a rock similar in composition to granite, but having the mica replaced by hornblende, which by its decomposition yields supplies of lime and magnesia more readily than they can be obtained from the less easily disintegrated mica. For this reason soils produced from the syenitic rocks are frequently possessed of considerable fertility.

The series of rocks of which greenstone and trap are types, and which are very widely distributed, differ greatly in composition from those already mentioned. They are divisible into two great classes, which have received the names of diorite and dolerite, the former a mixture of albite and hornblende, the latter of augite and labradorite, sometimes with considerable quantities of a sort of oligoclase containing both soda and lime, and of different kinds of zeolitic minerals. Generally speaking, the soils produced from diorite are superior to those from dolerite. The albite which the former contains undergoes a rapid decomposition, and yields abundance of soda along with some potash, which is seldom altogether wanting, while the hornblende supplies both lime and magnesia. Dolerite, when composed entirely of augite and labradorite, produces rather inferior soils; but when it contains oligoclase and zeolites, and comes under the head of basalt, its disintegration is the source of soils remarkable for their fertility; for these latter substances undergoing rapid decomposition furnish the plants with abundant supplies of alkalies and lime, while the more slowly decomposing hornblende affords the necessary quantity of magnesia. In addition to these, the basaltic rocks are found to contain appreciable quantities of phosphoric acid, so that they are in a condition to yield to the plant almost all its necessary constituents.

The different rocks now mentioned, with a few others of less general distribution, constitute the whole of our great mountain masses; and while their general composition is such as has been stated, they frequently contain disseminated through them quantities of other minerals which, though in trifling quantity, nevertheless add their quota of valuable constituents to the soils. Moreover, the exact composition of the minerals of which the great masses of rocks are composed is liable to some variety. Those which we have taken as illustrations have been selected as typical of the minerals; but it is not uncommon to find albite containing 2 or 3 per cent of potash, labradorite with a considerable proportion of soda, and zeolitic minerals containing several per cent of potash, the presence of which must of course considerably modify the properties of the soils produced from them. They are also greatly affected by the mechanical influences to which the rocks are exposed; and being situated for the most part in elevated positions, they are no sooner disintegrated than they are washed down by the rains. A granite, for instance, as the result of disintegration, has its felspar reduced to an impalpable powder, while its quartz and mica remain, the former entirely, the latter in great part, in the crystalline grains which existed originally in the granite. If such a disintegrated granite remains on the spot, it is easy to see what its composition must be; but if exposed to the action of running water, by which it is washed away from its original site, a process of separation takes place, the heavy grains of quartz are first deposited, then the lighter mica, and lastly the felspar. Thus there may be produced from the same granite, soils of very different nature and composition, from a pure and barren sand to a rich clay formed entirely of felspathic debris.

The sedimentary or stratified rocks are formed of particles carried down by water and deposited at the bottom of the primeval seas from which they have been upheaved in the course of geological changes. The process of their formation may be watched at the present day at the mouths of all great rivers, where a delta composed of the suspended matters carried down by the waters is slowly formed. The nature of these rocks must therefore depend entirely on that of the country through which the river flows. If its course runs through a country in which lime is abundant, calcareous rocks will be deposited, and if it passes through districts of different geological characters the deposit must necessarily consist of a mixture of the disintegrated particles of the different rocks the river has encountered. For this reason it is impossible to enter upon a detailed account of their composition. It is to be observed, however, that the particles of which they are composed, though originally derived from the crystalline rocks, have generally undergone a complex series of changes, geology teaching that, after deposition, they may in their turn undergo disintegration and be carried away by water, to be again deposited. Their composition must therefore vary not merely according to the nature of the rock from which they have been formed, but also according to the extent to which the decomposition has gone, and the successive changes to which they have been exposed. They may be reduced to the three great classes of clays, including the different kinds of clay slates, shales, etc., sandstone and limestone. It must be added also, that many of them contain carbonaceous matters produced by the decomposition of early races of plants and animals, and that mixtures of two or more of the different classes are frequent.

The purest clays are produced by the decomposition of felspar, but almost all the crystalline rocks may produce them by the removal of their alkalies, iron, lime, etc. Where circumstances have been favourable, the whole of these substances are removed, and the clay which remains consists almost entirely of silica and alumina, and yields a soil which is almost barren, not merely on account of the deficiency of many of the necessary elements of plants, but because it is so stiff and impenetrable that the roots find their way into it with difficulty. It rarely happens, however, that decomposition has advanced so far as to remove the whole of the alkalies, which is exemplified by the following analyses of the fire clay of the coal formation, and of transition clay slate:—

Transition Fire Clay. Clay Slate.

Silica 60.03 54.77 Alumina 14.91 28.61 Peroxide of iron 8.94 4.92 Lime 2.08 0.58 Magnesia 4.22 1.14 Potash 3.87 1.00 Soda — 0.24 Carbonic acid } 5.67 8.24 Water } —— —— 99.72 99.50

The sandstones are derived from the siliceous particles of granite and other rocks, and consist in many cases of nearly pure silica, in which case their disintegration produces a barren sand, but they more frequently contain an admixture of clay and micaceous scales, which sometimes form a by no means inconsiderable portion of them. Such sandstones yield soils of better quality, but they are always light and poor. Where they occur interstratified with clays, still better soils are produced, the mutual admixture of the disintegrated rocks affording a substance of intermediate properties, in which the heaviness of the clay is tempered by the lightness of the sandstone.

Limestone is one of the most widely distributed of the stratified rocks, and in different localities occurs of very different composition. Limestones are divided into two classes, common and magnesian; the former a nearly pure carbonate of lime, the latter a mixture of that substance with carbonate of magnesia. But while these are the principal constituents, it is not uncommon to find small quantities of phosphate and sulphate of lime, which, however trifling their proportions, are not unimportant in an agricultural point of view. The following analyses will serve to illustrate the general composition of these two sorts of limestone as they occur in the early geological formations:—

COMMON. MAGNESIAN. - Mid-Lothian. Sutherland. Sutherland. Dumfries.

Silica 2.00 7.42 6.00 2.31 Peroxide of iron } 0.45 0.76 1.57 2.00 and alumina } Carbonate of lime 93.61 84.11 50.21 58.81 Carbonate of } 1.62 7.45 41.22 36.41 magnesia } Phosphate of lime 0.56 ... ... ... Sulphate of lime 0.92 ... ... 0.10 Organic matter 0.20 ... ... ... Water 0.50 ... 0.69 ... —— —— —— —— 99.86 99.74 99.69 99.63

These limestones are hard and possess to a greater or less extent a crystalline texture. They are replaced in later geological periods by others which are much softer, and often purer, of which the oolitic limestones, so called from their resemblance to the roe of a fish, and chalk are the most important. Other limestones are also known which contain an admixture of clay. The soils produced by the disintegration of limestone and chalk are generally light and porous, but when mixed with clay, possess a very high degree of fertility, and this is particularly the case with chalk, which yields some of the most valuable of all soils. But it is true only of the common limestones, for experience has shown that those which contain magnesia in large quantity are often prejudicial to vegetation, and sometimes yield barren or inferior soils.

Such are the general characters of the three great classes of stratified rocks; any attempt to particularise the numerous varieties of each would lead us far beyond the limits of the present work. It is necessary, however, to remark, that in many instances one variety passes into the other, or, more correctly speaking, sedimentary rocks occur, which are mixtures of two or more of the three great classes. In fact, the name given to each really expresses only the preponderating ingredient, and many sandstones contain much clay, shales and clay slates abound in lime, and limestones in sand or clay, so that it may sometimes be a matter of some difficulty to decide to which class they belong. Such mixtures usually produce better soils than either of their constituents separately, and accordingly, in those geological formations in which they occur, the soils are generally of excellent quality. The same effect is produced where numerous thin beds of members of the different classes are interstratified, the disintegrated portions being gradually intermixed, and valuable soils formed.

The fertility of the soils formed from the stratified rocks is also increased by the presence of organic remains which afford a supply of phosphoric acid, and which are sometimes so abundant as to form a by no means unimportant part of their mass. They do not occur in the oldest sedimentary rocks, but as we ascend to the more recent geological epochs, they increase in abundance, until, in the greensands and other recent formations, whole beds of coprolites and other organic remains are met with. Great differences are observed in the quality of the soils yielded by different rocks. In general, those formed by the disintegration of clay slates are cold, heavy, and very difficult and expensive to work; those of sandstone light and poor, and of limestone often poor and thin. These statements must, however, be considered as very general; for individual cases occur in which some of these substances may produce good soils, remarkable exceptions being offered by the lower chalk and some of the shales of the coal formation. Little is at present known regarding the peculiar nature of many of these rocks, or their composition; and the cause of the differences in the fertility of the soil produced from them is a subject worthy of minute investigation.

Chemical Composition of the Soil.—Reference has been already made to the division of the constituents of the soil into the two great classes of organic and inorganic. And when treating of the sources of the organic constituents of plants, we entered with some degree of minuteness into the composition and relations of the different members of the former class, and expressed the opinion that they did not admit of being directly absorbed by the plant. But though the parts then stated lead to the inference that, as a direct source of these substances, humus is unimportant, it has other functions to perform which render it an essential constituent of all fertile soils. These functions are dependent partly on the power which it has of absorbing and entering into chemical composition with ammonia, and with certain of the soluble inorganic substances, and partly on the effect which the carbonic acid produced by its decomposition exerts on the mineral matters of the soil. In the former way, its effects are strikingly seen in the manner in which ammonia is absorbed by peat; for it suffices merely to pour upon some dried peat a small quantity of a dilute solution of ammonia to find its smell immediately disappear. This peculiar absorptive power extends also to the fixed alkalies, potash and soda, as well as to lime and magnesia, and has an important effect in preventing these substances being washed out of the soil—a property which, as we shall afterwards see, is possessed also by the clay contained in greater or less quantity in most soils. On the other hand, the air and moisture which penetrate the soil cause its decomposition, and the carbonic acid so produced attacks the undecomposed minerals existing in it, and liberate the valuable substances they contain.

In considering the composition of a soil, it is important to bear in mind that it is a substance of great complexity, not merely because it contains a large number of chemical elements, but also because it is made up of a mixture of several minerals in a more or less decomposed state. The most cursory examination shows that it almost invariably contains sand and scales of mica, and other substances can often be detected in it. Now it has been already observed that the minerals of which soils are composed, differ to a remarkable extent in the facility with which they undergo decomposition, and the bearing of this fact on its fertility is a matter of the highest importance, for it has been found that the mere presence of an abundant supply of all the essential constituents of plants is not always sufficient to constitute a fertile soil. Two soils, for instance, may be found on analysis to have exactly the same composition, although in practice one proves barren and the other fertile. The cause of this difference lies in the particular state of combination in which the elements are contained in them, and unless this be such that the plant is capable of absorbing them, it is immaterial in what quantity they are present, for they are thus locked up from use, and condemn the soil to hopeless infertility.

It is admitted that unless the substances be present in a state in which they can be dissolved, the plant is incapable of absorbing them; but it is a matter of doubt whether it is necessary that they be actually dissolved in the water which permeates the soil, or whether the plant is capable of exercising a directly solvent action. The latter view is the most probable, but at the same time it cannot be doubted, that if they are presented to the plant in solution, they will be absorbed in that state in preference to any other. Hence it has been considered important in the analysis of a soil, not to rest content with the determination of the quantity of each element it contains, but to obtain some indication of the state of combination in which it exists, so as to have some idea of the ease or difficulty with which they may be absorbed. For this purpose it is necessary to determine, 1st, The substances soluble in water; 2d, Those insoluble in water, but soluble in acids; 3d, Those insoluble both in water and acids; and if to these the organic constituents be added, there are four separate heads under which the components of a soil ought to be classified. This classification is accordingly adopted in the most careful and minute analyses; but the difficulty and labour attending them has hitherto precluded the possibility of making them except in a few instances; and, generally speaking, chemists have been contented with treating the soil with an acid, and determining in the solution all that is dissolved. Such analyses are often useful for practical purposes, as for example, when they show the absence of lime, or any other individual substance, by the addition of which we may rectify the deficiency of the soil; but they are of comparatively little scientific value, and throw but little light on the true constitution of the soil, and the sources of its fertility. Nor is it likely that much satisfactory information will be obtained until the number of minute analyses is so far extended as to establish the fundamental principles on which the various properties of the soil depends.

The separation of the constituents of a soil into the four great groups already mentioned, is effected in the following manner:—A given quantity of the soil is boiled with three or four successive quantities of water, which dissolves out all the soluble matters. These generally amount to about one-half per cent of the whole soil, and consist of nearly equal proportions of organic and inorganic substances. In very light and sandy soils, it occasionally happens that not more than one or two-tenths per cent dissolve in water, and in peaty soils, on the other hand, the proportion is sometimes considerably increased, principally owing to the abundance of soluble organic matters.

When the residue of this operation is treated with dilute hydrochloric acid, the matters soluble in acids are obtained in the fluid. The proportion of these substances is liable to very great variations, and in some soils of excellent quality, and well adapted to the growth of wheat, it does not exceed 3 per cent; while in calcareous soils, such as those of the chalk formation, it may reach as much as 50 or 60 per cent. In general, however, it amounts to about 10 per cent. The organic constituents are also very variable in amount; ordinary soils of good quality containing from 2 to 10 per cent, while in peat soils they not unfrequently reach 30 or even 50 per cent. But these cannot be considered fertile soils. The insoluble constituents are likewise subject to great variations, but, in the ordinary clay and sandy soils of this country, they generally form from 70 to 85 per cent of the whole.

The distribution of the constituents under these different heads will be best illustrated by a few analyses of soils of good quality, and for this purpose we shall select two, noted for the excellent crops of wheat they produce, and for their general fertility. The analyses were made from the upper 10 inches, and a quantity of the 10 inches immediately subjacent was analysed as subsoil. The first is the ordinary wheat soil of the county of Mid-Lothian, the other the alluvial soil of the Carse of Gowrie in Perthshire, so celebrated for the abundance and luxuriance of the crops it produces.

- Mid-Lothian. Perthshire. - - Soil. Subsoil. Soil. Subsoil. - - SUBSTANCES SOLUBLE IN WATER. Silica 0.0149 0.0104 0.0072 0.0461 Lime 0.0300 0.0072 0.0184 0.0306 Magnesia 0.0097 0.0016 0.0040 0.0034 Chlor. of magnesium 0.0033 Potash 0.0034 0.0037 Soda 0.0065 0.0049 Chloride of potassium 0.0088 0.0080 Chloride of sodium 0.0110 0.0166 Sulphuric acid 0.0193 0.0124 0.0089 0.0239 Chlorine trace trace Organic matters 0.1481 0.2228 0.0608 0.1342 - - 0.2319 0.2630 0.1191 0.2661 - - SOLUBLE IN ACIDS. Silica 0.1490 0.0680 0.0482 0.1697 Peroxide of iron 5.1730 3.4820 4.8700 4.6633 Alumina 2.1540 1.8130 2.6900 3.9070 Lime 0.4470 0.3810 0.3616 0.5050 Magnesia 0.4120 0.2850 0.3960 0.9420 Potash 0.0650 0.1650 0.3445 0.1670 Soda 0.0050 0.0560 0.1242 0.1920 Sulphuric acid 0.0250 0.0850 0.0911 0.0160 Phosphoric acid 0.4300 0.1970 0.2400 0.2680 Carbonic acid 0.0500 - - 8.8600 6.5320 9.2156 10.8300 - - INSOLUBLE IN ACIDS. Silica 71.3890 82.5090 63.1400 61.4200 Alumina 4.7810 3.5120 11.3500 10.3400 Peroxide of iron trace trace 1.5670 Lime 0.7520 0.5500 0.4500 0.7400 Magnesia 0.6610 0.5500 0.6200 0.4450 Potash 0.2860 2.4500 2.0030 Soda 0.4220 1.3100 0.8440 - - 78.2910 87.1210 79.3200 77.3590 - - ORGANIC MATTERS. Insoluble organic } matter } 8.8777 4.2370 7.7400 6.2910 Humine 0.8850 0.3450 0.0700 0.0840 Humic acid 0.1340 0.0310 0.6800 0.3600 Apocrenic acid 0.1533 0.0929 Water 2.6840 1.7670 2.7000 4.5750 - - 12.7340 6.3800 11.1900 11.4020 ======== ======== ====== ====== Sum of all the constituents 100.1169 100.2960 99.8447 99.8571 AMOUNT OF CARBON, HYDROGEN, NITROGEN, AND OXYGEN CONTAINED IN 100 PARTS OF EACH SOIL. Carbon 4.510 1.3060 2.55 2.03 Hydrogen 0.550 0.3324 0.71 0.53 Nitrogen 0.220 0.0973 0.21 0.17 Oxygen 4.918 3.1001 5.08 4.09 - - 10.198 4.8358 8.55 6.82 -

In examining these analyses, it is particularly worthy of notice that by far the larger proportion of the substances soluble in water consists of organic matter, lime, and sulphuric acid, the two last being in combination as sulphate of lime, while some of those substances which are usually considered to be the most important mineral constituents of plants are present in very small quantity—potash, for instance, forming not more than 1-25,000th of the whole soil, and phosphoric acid being entirely absent. On the other hand, this portion contains the whole of the chlorine which exists in the soil, and this might be anticipated from the ready solubility in water of the compounds of that substance.