Plant Growth and Anatomy: Meristems, Tissues, and Structures

Primary Meristem

Located at the tips of juvenile plant organs such as roots, shoots, and buds, the primary meristem is responsible for the plant's growth in length.

Root

The root has several distinct parts: the suberized zone, the zone of absorption, the growth area, and the root cap.

The growth zone, located near the root tip, contains meristematic tissue. This tissue can have one, two, or three meristematic cells. If there is one cell, it gives rise to all other cells. If there are three cells, they multiply and differentiate into the root cap and epidermis (lower cells), the cortex (middle cells), and the vascular cylinder (upper cells).

Shoot

Shoots do not grow in the opposite direction of roots. Shoots have nodes, internodes, and buds.

Buds are small outgrowths containing meristematic tissue that form branches, leaves, or flowers. Buds can be terminal (located at the tip of the stem) or lateral (located at the axils of leaves).

The meristem in the terminal bud causes the stem to grow in length. The cells formed give rise to the epidermis (upper cells), the cortex (middle cells), and the vascular cylinder (lower cells).

Secondary Meristem

Located in older plant organs, the secondary meristem appears after the first year of life. The cambial meristem is responsible for growth in thickness. The accidental meristem forms when the stem is wounded and helps in healing.

Protective Tissues

Epidermis

The epidermis covers the entire plant and can be found on the upper and/or lower surfaces of leaves. It protects the plant from harmful atmospheric variations.

Epidermal Formations

• Trichomes: Elongated, sometimes branched cells located on stems and leaves. They offer protection and can secrete substances. Example: Stinging hairs of nettles.
• Stomata: Microscopic pores found in the epidermis, particularly on leaves. They are formed by specialized cells and regulate gas exchange.

Cork

Cork tissue forms when the epidermal layer is replaced by layers of suberized (dead or living) cells. These flattened, square cells are impermeable to liquids and gases. Cork is found on stems and provides protection.

Support Tissues

Collenchyma

• Living cells
• Prismatic and elongated cells
• Cellulosic and flexible cell walls, thickened at the angles
• Located in young stems, petioles, and flower stalks
• Provides flexible support

Sclerenchyma

• Dead cells
• Short cells (sclereids) or elongated fibers
• Lignified, hard, and thick cell walls with pores
• Located in mature organs such as old stems and branches
• Provides rigid support

Sclerenchyma fibers can be lignified or non-lignified.

• Lignified fibers: Rigid and short, these fibers provide strength and are found in wood.
• Non-lignified fibers: Longer than lignified fibers, these flexible fibers have various industrial applications.