Palisade Tissue

Palisade Tissue 

a type of assimilative parenchyma of the leaf or, rarely, the stem. The palisade tissue consists of compactly arranged thin-walled cells lying with their long axes perpendicular to the surface of the leaf or stem. The tissue is usually located beneath the upper epidermis. The region underneath the palisade tissue consists of spongy tissue that has numerous intercellular spaces.

Under conditions of good illumination, palisade tissue consists of several layers of cells or constitutes the entire assimilative tissue of the leaf (for example, in pistachio). In plants that live under arid climatic conditions and bright illumination (for example, eucalyptus) and in plants with vertically arranged leaves (for example, narcissus), the palisade tissue is developed on both sides of the leaf. Sometimes it consists of palmate cells, whose membranes form deep folds that protrude into the cavity of the cell (for example, in black elder and aconite). In some species of wormwood, the subepidermal layer of palisade tissue performs a water-storing function; the assimilative functions are assumed by lower cells.