Stomata are often absent, absorption and excretion of gases in solution being carried on through the epidermal layer.
The epidermal cells may contain chlorophyll.
The uppermost is a purely muscular cell from the sub-umbrella; the two lower are epidermo-muscular cells from the base of a tentacle; the upstanding nucleated portion forms part of the epidermal mosaic on the free surface of the body.
U.e., Upper epidermal cells, with (c) cuticle.
In a few cases there is a special surface or epidermal layer, but usually all the outer layers of the stem are composed of brown, thick-walled, lignified, prosenchymatous, fibre-like cells forming a peripheral stereom (mechanical or supporting tissue) which forms the outer cortex.