Mark (botany)

from Wikipedia, the free encyclopedia
Mark in the elder branch

The pith is a soft substance in the core area of ​​plant shoot axes . It is the innermost tissue of the shoot and root.

In botany the softer cell tissue in stem-shaped thallus structures , in the stem and in the roots of the higher plants, is called the pith.

Due to the vascular bundles arranged in a ring , a shoot is divided into two zones in its shoot axis (called stalk in herbaceous plants , known as trunk in woody plants ):

Inner pith (0) and the pith rays (green)

The marrow is centrally located and is always characterized by a pronounced parenchymatic cell shape and usually consists of the widest cells of the stem. The stripes of the ground tissue located between the vascular bundles and connecting the pith and bark are also called pith rays .

In the stems of many herbaceous plants and some woody plants (for example the elderberry ) the cell membranes of this tissue are weakly thickened, the content has often disappeared from the cells and replaced by air, the cell itself has died. Sometimes there are wide, airy passages between the cells, which is also the reason for the characteristic lightness, softness and white color of such a marrow.

In some stems of herbaceous plants, the marrow cells even die in the first period of life, before the stem has finished growing. They are torn apart and disappear and the stem is then hollow in the adult state (medullary cavity of the grasses ). In the case of wood , the pulp is mostly permanent, the cell membranes of the same are more or less thickened and lignified and in the winter the starch is deposited in the cells. Nowhere does the marrow increase in size with old age. In older tree trunks, it usually passes with the innermost parts of the wood, which begins the hollowing of the trunk.