1442. In the highest, or the pinnate, leaves, movements, which are probably a result of the tracheal irritability, also occur, but are devoid the object of coming into contact with, or of touching, anything. The sensitive plants, as Hedysarum gyrans, move their leaves, not from any intrinsic determination upon their part, but in accordance with an antecedent stimulus, and thus not voluntarily, but probably through the influence merely of polar tension. The movements of leaves are convulsions of plants, although too an afflux of sap be caused or induced by the stimulus. SAP-MOTION. _Galvanic Process._ 1443. _The motion of the sap is imparted through the antagonism of the respiratory and digestive processes._ For these two processes are the combination of the Chemical with the Electric, which is the galvanism. 1444. The galvanic poles attract and repel the fluidity; thus the vegetable sap is attracted by the root and by the stalk. But the differencing or the oxygen pole is the stronger of the two. The determining principle of the movement of the sap resides consequently in the stalk, and the chief direction of the sap-motion tends upwards. 1445. At times, when the air-polarity is elevated, the sap also ascends more rapidly. As in summer, upon clear warm days. It ascends slowly upon gloomy and chill days. That in this also light and heat are playing their parts, is self-intelligible. Thereby the upper particles of sap become lighter and ascend, being pressed upwards by the lower and colder particles. As they are nevertheless by no means changed, this is a proof that, during the time so employed, polar forces also act upon them. 1446. But the root has also the endeavour to attract the sap; but as its pole is feebler in character, the stalk draws the sap from the ultimate extremities of the root into itself. If accordingly the polarity of the air becomes weaker, while the plant is losing its leaves or the organs of polarization; so is it easy to imagine why the motion of the sap becomes slower. As, however, the aerial polarity is always stronger than that of the earth, the sap must thus in winter also take the same, or upward, direction. 1447. A fall or descent of the sap can therefore never take place abstractedly forsooth from the root, in which it sinks by its own gravity. How a part of a plant, e. g. a twig, could continue alive, were the sap to have fallen or receded from it, is not to be conceived. It does not follow from what has been just stated, that movements of sap should not take place in all directions, and consequently too downwards; they must indeed occur rather than otherwise, and that indeed upon all sides; only the principal track or course of the sap must always pass in the direction upwards.