Plant Tissues

Plant Histology Parenchyma Collenchyma Sclerenchyma Xylem Tissue Phloem Tissue

Parenchyma Plant cells with thin cell wall and living protoplasm Roughly isodiametric with intercellular spaces Found in cortex and pith of stems and root, mesophyll of leaves and packing tissues in xylem and phloem

Function of Parenchyma Act as packing tissues between more specialized tissues Turgidity of these cells can provide support in herbaceous plant Store food Intercellular air spaces allow gaseous exchange Metabolically active Their cell walls are important pathway for the water and mineral salts through the plant

Collenchyma Characterized by the deposition of extra cellulose at the corners of the cells so have thickening cell wall of their corners They are living cells Found in regions beneath the epidermis of stem (hypodermis) and near the vascular tissues, eg, midrib of leaves

Sclerenchyma Plant cells with uniformly thickened cell wall which is usually lignified They are dead cells Support the cells There are two types: fibres and Sclerids

Fibre Long narrow cell shape with tapering ends, wall with few piths Found in cortex, pericycle, vascular tissues, surrounding vascular bundles

Sclereids Shorter, vary much in shape, may be spherical, polyhedral, elongated or branched with numerous pits Found in almost everywhere in plant body, especially in cortex, phloem of stems and roots, in fruit wall and seed coat Act as main cell type for mechanical support

Xylem Tissue Tracheary elements (tracheids, vessels) which are dead and empty cells for conducting water and support

Tracheids Narrow elongated cell with finely tapering ends, without protoplasm at maturity, with heavily lignified and pitted secondary cell wall Passage of water from cell to cell is facilitated through pit-pairs which allow lateral transport of water Act as the only water conducting elements in gymnosperms and primitive vascular plant; small amount in angiosperms

Vessel I Long, pipe-like cell shape, with complete or incomplete perforation at the end wall Without protoplasm at maturity Join each other at perforated end walls to form longitudinal conducting tubes Shorter, greater in diameter than tracheids

Vessel II Water moves from cell to cell through perforations and pit pairs Cell wall lignified and strengthened to prevent collapse More specialized for water conducting than tracheids Only present in angiosperms

Diagram of Phloem

Phloem Tissue Sieve elements (sieve cells, sieve tube elements) for conduction of food materials Sieve elements are elongated cells, cell wall with sieve areas Sieve elements is absence of nucleus, tonoplast, decrease in number of ER and ribosomes, with thin layer cytoplasm to facilitate the translocation of food

Sieve Cell With sieve areas evenly distributed Present in gymnosperms and lower vascular plant

Sieve Tube Element Located on the end walls called sieve plates Connected by sieve plates with each other to form sieve tube Present in angiosperms With companion cell to help translocation of food