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.
B. Vascular Processes.
a. Vessel-process—Conveyance of Sap.
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.
1400. The vessels of plants are notwithstanding to be compared with the lymphatic vessels of animals, in so far also as these are distributed throughout the whole body, and convey the sap simply in one direction not in a circle.
1401. As the passages between all the cells are in all directions, so the vegetable saps or fluids flow in all directions, and not to one centre as in the animal. Plants have no heart. The sap pursues a tolerably rapid course in the vessels. A fading or drooping cabbage, two feet in length, can gradually become erect in a few minutes after being put to soak in water. In other respects the course of the sap in the vessels may be seen in many plants under the microscope.
b. Liber-process—Mixture of Sap.
1402. In the liber, as being the mass of intercellular passages, the sap contained in the vessels principally accumulates, as in the thoracic duct of animals; in it the matters have not been simply conveyed and dissolved, but also mixed and converted into true vegetable sap, into blood.
1403. The tubes of the liber are those by which the chemical life is sustained.
c. Stalk-process—Secretion.