A violent thunderstorm, prolonged drought, herbivorous animal, or any other aggressive agent in the environment must be dealt with by the still plant, as opposed to an animal that can take refuge in a safe place until environmental conditions normalize.
The protective, or lining, tissues of a tracheophyte are the epidermis and the sub. Their efficiency can guarantee the protection of the plant against various aggressive agents of the environment.
It is a lining tissue in roots and trunks - hence in thick, mature tree plants formed by several layers of dead cells.
Cell death in this case is due to the impregnation of thick layers of suberin (a lipid material) in the cell walls that thus become hollow. As it stores air, the subber acts as an excellent thermal insulator, and of course plays an efficient protective role.
The trunk of a tree periodically grows in thickness. This growth forces the rupture of the subar that cracks at many points and eventually stands out, along with other tissues. First, however, the tree elaborates a new sub that will replace what will fall. This periodically highlighted material is called ritidoma.
The epidermis of vascular plants is a tissue generally formed by a single layer of irregularly shaped, flat, living and non-chlorinated cells. It is a typical lining tissue of young organs (root, stem and leaves). The epidermis of a root shows a cylindrical layer of lining, with a piliferous zone, whose hairs are nothing but extensions of an epidermal cell.
Primary root cross section of Mandevilla velutina. Ep = epidermis; Pr = root hair; Ex = exoderm; Pc = cortical parenchyma; En = endoderm; P = pericycle; Xp = primary xylem; Fp = primary phloem.
Young stems are also lined with a thin, non-endowed epidermis.
It is in the leaf that the epidermis has remarkable specializations: being a double-sided organ, it has two epidermis, the upper and the lower.
Epidermal cells secrete waterproofing substances, which form a coating film called a cuticle. The main component of cuticle It is cutin, a polymer made of fatty acid molecules. In addition to preventing water loss, the cuticle protects the plant against infections and mechanical trauma.