This consists typically of close-fitting layers of cells with completely suberized walls, intended to replace the epidermis as the external protective layer of the plant when the latter, incapable as it is of further growth after its original formation, is broken and cast off by the increase in thickness of the stem through the activity of the cambium.
The epidermis of a very large number of species bears hairs of various kinds.
In the epidermis itself (rarely), in any layer of the cortex, or in the pericycle.
- Stinging Hair of Urtica dioica, with a portion of the epidermis, and, to the right, a small bristle (X60).
Usually they are absent from the cells of the epidermis, though in some of the lower plants they are met with there also.