1070. The ultimate cause of this spiral motion, as well as the position of the parts, appears to reside in the rotation of the sun. 1071. Upon this also depends probably the winding of the stem of plants, with the spiral-shaped position of the leaves and branches, as probably even the contortions of the snail's shell and of the hairs upon the crown of the head. 1072. The production of the spiral form originates from the antagonism of the light with the matter. The number of spiral vessels is therefore less in those parts that are beneath, than in those above, the earth, or less in the root than the stem. The more indeed an organ has been exposed to the air, by so much the more do the spiral vessels preponderate, as e. g. in the leaves. 1073. An organ must necessarily be nobler in character, the more spiral vessels it contains. The plant also that, with more spiral vessels, exhibits them particularly arranged, must take a higher rank. The lowest plants, as the mushrooms, lichens and mosses, consist therefore entirely of cellular tissue; in the ferns therefore only a single bundle of spiral vessels makes its appearance. When plants become nobler, several fasciculi of spiral vessels originate; and in tracing this feature we ascend from the ferns to the grasses and lilies, up to the lower Dicotyledons. In the higher Dicotyledons the packets of the tracheæ increase for the first time to such a degree, that they form a closed circle, the fibrous ring or zone of wood. 1074. The tracheæ extend from one end of the plant to the other; many are wont to terminate only in nodes, while these are to be regarded as arrested branches. The air can therefore penetrate through the spiral vessels from the leaves even to the apices of the roots. II. _Anatomical Systems--Sheaths._ 1075. These originate by vagination and separation of the tissues in the transverse direction, and prevail throughout the whole plant. The idea of the whole vegetable structure is extremely simple. Originally the plant is a vesicle in water, or cellular tissue in the seed; root and stalk also consist in their main bulk or proportion of cellular tissue, which is called parenchyma. Therein the three planetary processes reside inclosed. Such a plant is still in the recognizable state of the primary organism. In the sequel, however, through the influence of light, the polarity between light and darkness issues forth in the parenchyma, the cellular tissue obtains a linear direction, and becomes elongated into spiral vessels. The spiral vessels form one or several fasciculi, which emerge out of the parenchyma, by which they, and each packet individually, are circularly surrounded. The cellular tissue is as it were the soil, in which the fasciculi of spiral vessels are rooted as proprietary plants and out of which they grow.