Elements of Physiophilosophy

by Lorenz Oken

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.

1076. The effort of the three vegetable processes, to separate their organs from, and perfect them independently of, each other, is in incessant operation, both from without inwards, as well as from above downwards, because in both cases is light there, darkness here, dryness there, humidity here. The cellular tissue, that has finally become independent in the transverse direction or from without inwards, is called bark, the self-substantial tubular tissue is called liber, the non-dependent tracheal tissue, wood.

1. TRACHEAL-SYSTEM, WOOD.

1077. With increased influence of light the tracheal fasciculi also increase, and form a circle of columns in the parenchyma around the centre of the plant. Between the column, externally and internally to the same, is the parenchyma. The more, however, the columns accumulate, by so much the more does it diminish, and whereas the columns previously stood singly in the parenchyma, the appearance is now as if narrow plates only of parenchyma traversed between the columns from without inwards. Finally the columns predominate to such an extent and approximate so closely, that the plates almost disappear. They are now called insertions of cellular tissue, or medullary rays. As the tracheæ convey air, and have thus been more exposed to the process of oxydation, they generally harden sooner than in other parts.

1078. Around the fasciculi of spiral vessels the cellular tissue also strives to elongate, and begins at the same time to harden. Such extended cells, in which the light has almost disappeared, are called fibres. Indurated tracheæ and fibres are called Wood. The wood is always in the vicinity of the spiral vessels. It is a production synchronous with the latter.

1079. Only, where spiral vessels are, can genuine wood originate; but it is not everywhere, where they are found, that woody fibres must be also present, although the cells extend around all bundles of spiral vessels. If the degree of oxydation of the cells be slight, they do not harden, but continue herbaceous in texture. The parenchyma has now been separated by a circle of fibrous columns into an external and internal, or peripheric and central. The central parenchyma becomes void of sap and spongy, because the plant imbibing its nutriment on the surface, and the air and the light operating thereupon, the processes conduct it thither. This withered parenchyma is called pith, which in accordance with its origin merits no physiological consideration, nor is worthy and susceptible of any philosophical construction.

2. TUBULAR SYSTEM, LIBER.

1080. As the plant draws in its nourishment from without, so is the main proportion of the sap necessarily present in the periphery of the spiral vessels. The elongated cells in the neighbourhood of the spiral vessels, and which principally contain sap, are called Liber.

1081. Liber is necessarily present around every packet of spiral vessels, and thus with fasciculi everywhere dispersed throughout the stem. The liber is only situated beneath the bark, when the number of the spiro-vascular fasciculi is so great, that they form a closed circle in the parenchyma; it is only beneath the bark, in so far as it accompanies the spiral vessels, but can only surround the latter from without. As it is only the woody plants that have been usually examined, the false idea has thus originated of the liber having, as it were from its very essence, to be beneath the bark.