trichome and stomata, Slides of Pharmacognosy

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PG 101

Section 3 Dermal tissues

II-Dermal tissue

 The epidermis is the outer most layer of dermal layer which is a single-layered group of cells that covers plants' leaves, flowers, roots and stems.  The walls of the epidermal cells are covered with a cuticle which reduces water loss to the atmosphere and forms a boundary between the plant and the external environment.

Histology

 The walls may be straight, wavy or beaded and often covered with a layer of cuticle made up of cutin.

Special structures in Epidermis

Epidermis Stomata Trichomes

Stomata

 In the plant body. They are most abundant in the lower epidermis of a dorsiventral leaf and less abundant on the upper epidermis.  In isobilateral leaves, stomata remain confined to the upper epidermis alone  in submerged leaves no stoma is present

Types of stomata

Stomata Dicot Paracytic Diacytic Anomocytic Anisocytic Monocot Dumbbell shaped

Paracytic stomata Surrounded by 2 subsidiary cells of which the long axis are parallel to the axis of stoma.

Diacytic stomata Surrounded by 2 subsidiary cells of which the common wall of which is at right angles to the stoma

Anomocytic stomata Surrounded by varying number of cells which are not differentiated from those of the epidermis

Trichomes

 Trichomes are more elongated outgrowths

of one or more epidermal cells which looks

like hairs.

 protect the plant against intense

illumination (i.e. strong sunlight) and

excessive radiation of heat.

 may have secretory functions.

Trichomes

(hairs)

Non glandular trichome Glandular trichome

Non glandular trichomes

Unicellular tr.