50 lbs. of carbon with 50 of water, make 100 of woody fibre. 50 lbs. 37½ 87½ of ulmic acid. { of cane sugar, 50 lbs. 72½ 122½ { of starch, or { of gum. 50 lbs. 56 106 of vinegar. In the interior of the plant, therefore, it is obvious that, whichever of these substances be present in the sap, the elements are at hand out of which any of the others may be produced. In what way they really are produced, the one from the other, and by what circumstances these transformations are favoured, it would lead into too great detail to attempt here to explain.[6] We cannot help admiring to what varied purposes in nature the same elements are applied, and from how few and simple materials, substances, the most varied in their properties, are in the living vegetable daily produced. [6] For fuller and more precise explanations on these interesting topics, see the Author’s LECTURES _on Agricultural Chemistry and Geology_, Part I. CHAPTER IV. Of the Inorganic Constitution of Plants—Their immediate Source—Their Nature—Quantity of each in certain common Crops. SECTION I.—SOURCE OF THE EARTHY MATTER OF PLANTS—SUBSTANCES OF WHICH IT CONSISTS. When plants are burned, they always leave more or less of ash behind. This ash varies in quantity in different plants, in different parts of the same plant, and sometimes in different specimens of the same kind of plant, especially if grown upon different soils; yet it is never wholly absent. It seems as necessary to their existence in a state of perfect health as any of the elements which constitute the organic or combustible part of their substance. They must obtain it therefore along with the food on which they live: it is in fact a part of their natural food, since without it they become unhealthy. We shall speak of it therefore as the _inorganic food_ of plants. We have seen that all the elements which are necessary to the production of the woody fibre, and of the other organic parts of the plant, may be derived either from the air, from the carbonic acid and watery vapour taken in by the leaves, or from the soil, through the medium of the roots. In the air, however, only rare particles of inorganic or earthy matter are known to float, and these in a solid form, so as to be unable to enter by the leaves; the earthy matter which constitutes the ash, therefore, must be all derived from the soil.