collenchyma cells are irregularly arranged. Cell wall is thickened on the walls bordering intercellular spaces. Example: Hypodermis of Ipomoea . Lamellar collenchyma The collenchyma cells are arranged compactly in layers(rows).
The Cell wall is thickened only at tangential wall. devoid of thickened at radial walls. These thickening appear as successsive tangential layers. Example: Hypodermis of Helianthus Diagramatic structures Nucleus Intercellular thickenings b.
Thickened corners Vacuole Cell wall Protoplasm a. Lamellar thickenings c. Figure . : Types of Collenchyma a) Angular collenchyma, b) Lacunar collenchyma, c) Lamellar collenchyma Annular Collenchyma: Duchaigne ( ) reported another type called Annular collenchyma in petiole of Nerium.
The lumen is more or less circular in shape. Sclerenchyma (Gk. Sclerous- hard: enchyma-an infusion) The sclerenchyma is dead cell and lacks protoplasm. The cells are long or short, narrow thick walled and lignified secondary walls.
The cell walls of these cells are uniformly and strongly thickened. sclerenchymatous cells are of two types: . Sclereids . Fibres Sclereids (Stone Cells) Sclereids are dead cells, usually these are isodiametric but some are elongated too.
The cell wall is very thick due to lignification. Lumen is very much reduced. The pits may simple or branched. Sclereids are mechanical in function.
They give hard texture to the seed coats, endosperms etc., Sclereids are classified into the following types. Thick cell wall Lumen cell Pith a. Macro Sclereid Lumen b. Lumen Thick cell wall c.
Tricho Sclereids e. Lumen Thick cell wall d. Figure . : Types of sclereids a) Brachysclereids, b) Macrosclereids, c) Osteosclereids, d) Astrosclereids, e) Trichosclereids .
Brachysclereids or Stone cells: Isodiametric sclereids, with hard cell wall. It is found in bark, pith cortex, hard endosperm and fleshy portion of some fruits. Example: - Pulp of Pyrus . .
Osteosclereids (Bone cells): Rod shaped with dilated ends. They occur in leaves and seed coats. Example: seed coat of Pisum and Hakea . Astrosclereids: Star cells with lobes or arms diverging from a central body.
They occur in petioles and leaves. Example: Tea, Nymphae and Trochodendron . . Trichosclereids: Hair like thin walled sclereids.
Numerous small angular