The source from whence the ascending sap is derived is the aliment absorbed by the roots from the soil. This aliment consists essentially of two substances; one of these being sufficiently familiar, namely, water; and the other commonly existing in the atmosphere under the form of gas or air, but likewise capable of solution in water, namely, carbonic acid; this substance is known to every one as the cause, by its escape, of the boiling appearance seen in freshly uncorked soda water. Those two substances constitute the necessary aliment of vegetables: at the same time it is notorious that various matters, such as manures, earths, &c., greatly facilitate the growth of plants; but these matters produce this effect either by supplying a greater quantity of carbonic acid, or by acting in a manner similar to condiments; for in the same way as spices taken into the stomach along with food invigorate the digestive power, so do many minerals, when absorbed by the roots, operate in promoting the nutrition of vegetables. The chemical composition of the ascending sap is chiefly a solution of sugar and gum in water. In the northern states of America, sugar in large quantities is obtained from some species of maple, principally the sugar maple and swamp maple of Canada, by boring the stem, collecting the ascending sap which flows from the wound, and evaporating away its watery portions. It is an interesting question, from whence proceed the sugar and gum contained in this ascending sap? The only satisfactory reply to this question is, that these substances become formed out of the water and carbonic acid absorbed from the soil; but this is a transformation which cannot be effected by the most expert chemist, so that we find in this, as in many other instances, a living body is a laboratory in which Nature executes changes far transcending the loftiest efforts of man’s ingenuity. The part of the vegetable through which the sap ascends can be easily shown in any of the ordinary trees of this country. If a branch from a currant shrub be placed with its inferior and newly cut surface immersed at first in a solution of green vitriol and afterwards in an infusion of nutgalls, the course through which these fluids ascend may be traced by the black colour produced by their mixture; for every one knows that a mixture of green vitriol and nutgalls produces ink, and in the experiment just described, the solutions of these substances following each other in their ascent, inscribe in a manner on the interior of the branch the path which they successively pursued. This course will be found to exist between the bark and the pith, these parts being quite unchanged, while the intermediate portion of wood will be deeply coloured.