1061. The fundamental form of the cells is the rhomboidal-dodecahedron (Kieser's Phytotomie); for around a globe only 6 others of equal size can be placed, whereby its 6 lateral surfaces are pressed in, which during the induration impart to it the form of a six-sided column. Above and below these 7 globes only 3 others admit of being placed, whereby 3 point-converging surfaces originate, which thus complete the middle globe as rhomboidal-dodecahedron. 2. EARTH-ORGAN, VASCULAR TISSUE. 1062. So long as the vesicles or cells lie as globes upon each other, triangular interspaces are found between them, which stand in conjunction with each other on all sides. As water is found in these interspaces, it is plain that they do not entirely disappear with the transformation of the cells into rhomboidal-dodecahedra. These spaces are called intercellular passages or sap-tubes, _Vessels_. In many plants, such as those which contain a milky juice, particular sap-tubes run through a part of these intercellular passages, and are probably formed by condensation of the sap. Both are therefore in a physiological respect of one kind. At bottom also the blood-vessels of animals are naught else but passages in felted cellular tissue. 1063. As the principal polarity of plants has been directed upwards, and the cells therefore been protracted lengthwise; so also the chief direction of the vessels is parallel with the axis of the plant. 1064. The vegetable sap ascends in these tubes, which must be therefore viewed indeed as constituting the earth-or nutritive organ. 3. AIR-ORGAN, TRACHEAL TISSUE. 1065. The plant is not merely earth-and water-organism, but also air-organism; and there must therefore be developed in it an anatomical system, which coincides with the process of air. 1066. Besides the cells and tubes naught else is found in vegetable tissue but spiral vessels; what are called scalariform tubes, annular vessels, dotted ducts, vermiform or strangulated vessels, are no peculiar formations in themselves, but only different conditions of the spiral vessels. 1067. The spiral vessels are the air-system of the plant, and therefore rightly deserve the name of _Tracheæ_. They exhibit the structure of the air-tubes in insects, and contain, according to the most authentic observations, air, and not sap, except in the period of adolescence, as occurs in the animal kingdom. 1068. The spiral vessels consist of one or several filaments spirally contorted, and held together by a delicate tubular-shaped membrane. 1069. They must be regarded as elongated cells, upon whose parietes the starch-granules have been placed in serial juxtaposition with each other, so as to form spirally-twisted filaments, as is to be plainly seen in many cells and also in Confervæ. This spiral condition originates without doubt from the spiral-shaped motion of the granules in cell-sap.