BIOLOGY Volume 1 - A Guide to General Biology - 2004

6. HISTOLOGY

6.1. Simple Plant Tissues (tissues consisting of cells of a single type)

6.1.2. Collenchyma

Like parenchyma, collenchyma consists of living Cells, but these cells are modified to suit its primary function of providing the plant body with support and mechanical strength.

Structure

The structure of collenchyma is shown in Fig. 6.5. In many respects, collenchyma resembles parenchyma, but it is characterized by the additional deposition of Cellulose in The Cell corners. This deposition occurs after the primary Cell wall has formed. In addition, collenchyma cells are elongated parallel to the long axis of the organ in which the tissue is found.

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Fig. 6.5. Structure of collenchyma cells. A. Transverse section. The cells are polygonal in shape. B. Longitudinal section. The cells are elongated (up to 1 mm in length). C. Transverse section. Collenchyma from a Helianthus stem. D. Longitudinal section. Collenchyma from a Helianthus stem.

Functions and Distribution

Collenchyma is a mechanical tissue that provides structural support to the plant Organs in which it is located. It plays a particularly crucial role in young plants, herbaceous plants, and organs such as leaves that lack Secondary Growth. In all these cases, collenchyma provides vital support to plant organs, complementing the effect produced by turgescent parenchyma. Collenchyma is the first supportive (skeletal) tissue to differentiate in the primary plant body. Because its cells remain alive, they are capable of growth and stretching, so they do not impede the growth of adjacent cells.

In stems and petioles, the supportive function of collenchyma is further enhanced by its peripheral Location within the organ. It is frequently situated directly beneath the epidermis in the outer cortex, gradually transitioning into parenchyma toward the center of the organ, effectively forming a hollow cylinder in three dimensions. In other cases, it may form ridges that increase the rigidity of the organ, such as in the fleshy petioles of celery (Apium graveolens) or the ribbed stems of plants like dead-nettle (Lamium). In dicotyledonous leaves, collenchyma surrounds the midrib and provides support to the vascular bundles (see Fig. 6.1).