3.  The produce of nitrogen in clover and peas, which agriculturists will acknowledge require no nitrogenised manure, is far greater than that of a potato or turnip field, which is abundantly supplied with such manures.

Lastly.  And this is the most curious deduction to be derived from the above facts,—­if we plant potatoes, wheat, turnips, peas, and clover, (plants containing potash, lime, and silex,) upon the same land, three times manured, we gain in 16 years, for a given quantity of carbon, the same proportion of nitrogen which we receive from a meadow which has received no nitrogenised manure.

On a morgen of meadow-land, we obtain in plants, containing silex, lime, and potash, 984 carbon, 32.2 nitrogen.  On a morgen of cultivated land, in an average of 16 years, in plants containing the same mineral elements, silex, lime, and potash, 857 carbon, 26.8 nitrogen.

If we add the carbon and nitrogen of the leaves of the beetroot, and the stalk and leaves of the potatoes, which have not been taken into account, it still remains evident that the cultivated fields, notwithstanding the supply of carbonaceous and nitrogenised manures, produced no more carbon and nitrogen than an equal surface of meadow-land supplied only with mineral elements.

What then is the rationale of the effect of manure,—­of the solid and fluid excrements of animals?

This question can now be satisfactorily answered:  that effect is the restoration of the elementary constituents of the soil which have been gradually drawn from it in the shape of grain and cattle.  If the land I am speaking of had not been manured during those 16 years, not more than one-half, or perhaps than one-third part of the carbon and nitrogen would have been produced.  We owe it to the animal excrements, that it equalled in production the meadow-land, and this, because they restored the mineral ingredients of the soil removed by the crops.  All that the supply of manure accomplished, was to prevent the land from becoming poorer in these, than the meadow which produces 2,500 pounds of hay.  We withdraw from the meadow in this hay as large an amount of mineral substances as we do in one harvest of grain, and we know that the fertility of the meadow is just as dependent upon the restoration of these ingredients to its soil, as the cultivated land is upon manures.  Two meadows of equal surface, containing unequal quantities of inorganic elements of nourishment,—­other conditions being equal,—­are very unequally fertile; that which possesses most, furnishes most hay.  If we do not restore to a meadow the withdrawn elements, its fertility decreases.  But its fertility remains unimpaired, with a due supply of animal excrements, fluid and solid, and it not only remains the same, but may be increased by a supply of mineral substances alone, such as remain after the combustion of ligneous plants and other vegetables; namely, ashes.  Ashes represent the whole nourishment which vegetables receive