Plant Tissue Systems and Types

Plant Tissue Systems

Plant tissues are responsible for growth and structure. They are broadly classified into meristematic and definitive tissues.

Meristematic Tissues

Meristematic tissues are responsible for plant growth. The cells are small, polyhedral in form, with thin walls and abundant small vacuoles initially.

• Apical Meristems: Responsible for primary growth in length of the plant. They are located at the ends of the root and stem.
• Lateral Meristems: Responsible for growth in girth or secondary growth. They are distributed throughout the plant. They produce vascular cambium (conducting tissue) and cork cambium (which gives rise to suber or cork).

Definitive Tissues (Fundamental Tissue System)

Definitive tissues are specialized and typically do not divide. They form the bulk of the plant body.

• Parenchyma

  These are living cells that maintain their capacity for division. They form a continuous mass with abundant cytoplasm content and have different functions (aquifer, aerenchyma, and chlorenchyma). They form the fundamental tissue.

• Collenchyma

  Collenchyma cells are alive, elongated, and have unevenly thickened walls. They act as support in young, growing plant bodies.

• Sclerenchyma

  Sclerenchyma cells have a thick, hard, lignified wall. They are usually dead and act as reinforcement and support for mature plant parts. Its types are:

  • Fibers: Elongated cords, raw material for many textile fibers.
  • Sclereids: Have variable form and are scattered throughout the fundamental tissue. They are abundant in seed coats.

Vascular System

Formed by two conducting tissues:

• Xylem

  The tissue conducting water and mineral salts from the roots to the rest of the plant. The hallmark of this tissue is the vessel or tracheary element.

• Phloem

  The tissue conducting photosynthetic sap from all parts of the plant. The characteristic cell is the sieve tube element.

Dermal System

Consists of two types of tissues:

• Epidermis

  The outermost layer of young plants, formed by a single layer of flattened, strongly united cells. Their outer walls are covered with a cuticle, formed by lipid-type waxes such as cutin, which protects against water loss.

  • Stomata: Formed by a pair of kidney-shaped cells with chloroplasts called guard cells. They regulate gas exchange between the inside and outside of the plant.
  • Trichomes (Hairs): Facilitate the absorption of water and salts.

• Periderm

  Replaces the epidermis in stems and roots with secondary growth. It consists mainly of suber or cork for protection.