BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VII. PLANT TISSUES

Mechanical Tissues

Sclerenchyma

A mechanical tissue consisting of fibers. The Cells are dead, elongated, prosenchymatous, tapered at the ends, with evenly thickened walls. They develop from procambium or cambium. Initially, the cells are alive, containing multinucleated Cytoplasm and thin walls with pits. Later, the walls thicken, the protoplast dies, and The Cell becomes filled with air. Individual sclerenchyma cells form an elementary fiber, while groups of them form a technical fiber.

Sclerenchyma fibers develop in almost all plant Organs. Based on Cell Structure characteristics and their localization within plant organs, they are classified into bast fibers and wood fibers (libriform fibers).

Bast fibers are located in the peripheral part of the plant and constitute a part of the bark (bast, phloem). Their cells are very long (5-300 mm) with heavily thickened walls. A distinction is made between Primary and secondary bast fibers. Primary bast fibers are formed by the procambium; they are thicker and longer, with pectic-cellulosic or lignified walls. Secondary bast fibers are formed by the cambium; they are thinner and 3-5 times shorter than the primary ones. Bast fibers resist the tension and bending of plant organs, providing them with elasticity. They serve as raw material for the textile and pulp-and-paper industries.

Wood fibers (libriform) are a component of xylem, or wood. Their cells are relatively short (up to 5 mm long). Cell walls are thickened due to Lignin. They are formed by both procambium and cambium and make up the bulk of hardwood timber. Libriform fibers withstand the downward pressure of the tree crown on the stem and are used as a building material as well as raw material for the pulp-and-paper and chemical industries.