1097. In the stalk, however, the opposition of tissues and systems emerges more strongly, and therefore they all become individualized also to a higher degree. The spiral vessels become more freed from the cellular tissue; the bark is more distinctly divided from the liber; this again from the wood, and in its centre the cellular tissue dries up into pith. As, however, the stalk is the first product of the light-influence, the tracheal system cannot attain as yet entire freedom. The cells have nevertheless been extended, and the intercellular passages are formed into regular tubes. The _Stalk_ is the trunk of the plant with a preponderating system of tubes. 1098. This separation of the tissues and systems, with the endeavour upon the part of each to become individually perfect and isolated from the other, is effected by the air and the light. As root imbibes the mucous or slimy water, and sustains the chemical process in the plant, so does the stalk set the water in motion, since it exposes it to the air and light, whereby the chemical earth-process becomes separated into different saps and elemental bodies. 1099. Through the influence of the air, light and heat upon the stalk, as well as by its antagonism with the root, its elongation is determined. The greater amount of energy of the aerial polarity is in the higher regions; it is thus more excited by these than by the lower, and the bud being lighter grows more rapidly in the upper parts, and obtains an elongated form. The excitation is stronger also upon the side exposed to the light. It grows also more strongly in that direction, and thus the stalk stands indeed upwards, but somewhat inclined from the perpendicular line towards the sun.