Plant Integumentary System
The epidermis is the main surface tissue of young plants and the covering material of all leaves. Usually the epidermis is one cell deep; its cells have thick outer and side walls. On the parts of the plant that are above
ground, the epidermal cells secrete an outer waxy cuticle that is water resistant. The thickened cell walls, together with the cuticle, prevent drying out, injury, and fungus infection. The epidermis in aerial parts of the plant gives rise to plant hairs, spines, and glands. In leaves, the epidermis develops guard cells that regulate the size of pores or stomata, which allows the exchange of gases with the atmosphere. The epidermis of roots lacks the waxy cuticle found in the parts of the plant above ground, allowing the root epidermis to absorb water from the soil. Root hairs that increase the absorbing surface of the root arise from epidermal tissue. When a plant grows in diameter, the epidermis is replaced by the periderm, in the stem and the roots. The periderm contains cork cells whose walls after cell death provide a protective waterproof outer covering for plants making up the bark of older trees.
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