1393. The bark, as an organ of cellular tissue, which is placed wholly in the outward direction, must principally exercise the process of absorption and evaporation. Now, as there are two kinds of bark, a root-and a stalk-bark, or a water-and air-bark, so upon the former will the business of absorption chiefly devolve, on the latter that of evaporation.
1394. As the bark of the stalk possesses stomata, which are wanting in that of the root, so is this a probable reason for these apertures being organs of evaporation. This opinion is corroborated also by aquatic leaves being without stomata, while they occur in the leaves exposed to air.
1395. Meanwhile the stalk is of a twofold character; it is only the root that has ascended into the air. As an aerial root it absorbs. Without doubt the stalk absorbs the same as the root, namely, moisture from the air and carbonic acid. Experiments prove it.
1396. The cells are the crystallized drops of mucus, the fundamental mass of the vegetable and consequently the water, which converts itself into the Earthy, or wherein the Solid has been elaborated and precipitated. They construct the Solid that has been absorbed into new cells. But the Solid can only assume other forms by means of water. The solution, however, with mixture of bodies and formation into globules is digestion. The cells are thus the stomachs of which the plant has millions like mouths.
1397. The bodies absorbed must move in the cells; for chemical solution and mixture, being itself nothing else than separation and union of atoms, is consequently motion. In a single cell the motion must be upon all sides, because the atoms are attracted and repelled from all points of the cell-wall. In cells, however, which are united with others and therefore subjected to longitudinal polarity, this motion must be performed in accordance with the axis of the cells.
1398. This motion proceeds to and fro, because the extremities of the cells have different polarities, and therefore repel the same atoms, which they have before attracted. In the cells the mucus appears to be converted into starch-granules.
1399. The vessels or intercellular passages conduct the sap, or the water of the plant. Their function is therefore the continued conveyance of the sap that has been absorbed from the root, and rendered solid or consistent by the evaporation going on in the bark and elaborated by the cells.