Plant Tissues and Their Functions

Protective Tissues

Epidermal Tissue

This outermost layer covers roots, herbaceous stems, and leaves. It consists of a single layer of living cells without chlorophyll, tightly arranged without spaces. The outer cell wall is covered with a cuticle, a waterproof layer made of cutin and waxes. In aerial parts, the epidermis protects stems and leaves, regulates perspiration, and facilitates gas exchange. In roots, it protects and aids water and salt absorption through root hairs. Trichomes, also present in the epidermis, provide additional protection.

Cork Tissue (Suber)

This tissue replaces the epidermal tissue in older plant parts. It comprises multiple layers of dead cells coated with suberin, making it highly waterproof. Due to cell activity, the lower layers continually regenerate. Lenticels, small pores in the suber, allow gas exchange with the atmosphere.

Secretory Tissues

These tissues secrete various substances, some considered waste products and others beneficial to the plant. They are categorized into two groups:

1. Cells and Glandular Tissue (External Secretions)

• Isolated cells within other tissues.
• Glandular epithelium, composed of detached cells.
• Glandular hairs, elongated cells extending outward, releasing resinous substances.
• Epidermal glands, secreting substances like gums and resins.
• Schizogenous cavities, intercellular spaces surrounded by glandular cells that release secretions into these spaces.

2. Cells and Tissues with Internal Secretions

These cells store products within vacuoles, releasing them only when the vacuoles rupture. Stored substances include mucilage, essences, and tannins. Laticiferous tubes, branching tubes formed by multinucleated cells, contain latex. Lytic cavities, formed by groups of cells with dissolved membranes, create vesicles for accumulating secretions.