Plant Tissues PDF

## Plant Tissues ### Ground tissues * **simple tissues** * parenchyma * collenchyma * sclerenchyma ### 1 - Parenchyma * **Characters:** * alive at maturity * have cellulosic thin wall * have intercellular spaces * Palisade parenchyma: cylindrical and elongated cells a...

## Plant Tissues ### Ground tissues * **simple tissues** * parenchyma * collenchyma * sclerenchyma ### 1 - Parenchyma * **Characters:** * alive at maturity * have cellulosic thin wall * have intercellular spaces * Palisade parenchyma: cylindrical and elongated cells at right angles to the epidermis and they contain chloroplasts. * The spongy parenchyma has large inter-cellular spaces that facilitate gas diffusion. * The spongy parenchyma also contains chloroplasts and contributes to photosynthesis. * The tissue specialized in photosynthesis is the mesophyll ### 2 - Collenchyma * **Simple living tissue, usually hypodermal in position and in corners of angular stems.** * **Have cellulosic thick wall** ### 3 - Sclerenchyma * Dead cells when mature with thick walls, used for mechanical support. * Sclerenchyma has two types: Fibers and sclereids. * Fibers: they are dead cells have pitted walled with narrow lumina and pointed apices * Sclereids: they are dead cells short, isodiametric, elongated or branched thick walled, lignified with branched lumina ### Vascular Tissues * **complex tissues** * Xylem: It is the water conducting tissue which consists of vessels, tracheids, parenchyma and fibers * Xylem Vessels: Each vessel is formed from a series of vessel elements jointed end by end. * Functions: vessels are used for transport and mechanical support. * Tracheids: long and tapered, with angled end-plates that connect cell to cell. * The function of tracheids is water transport and mechanical support. * Phloem: Phloem is the food conducting tissue which is formed of four elements: sieve tubes, companion cells, parenchyma and fibers. ### The transverse section of a leaf * **T.S** * Cuticle * Upper epidermis * Palisade mesophyll cell * Bundle sheath cell * Xylem * Phloem * Lower epidermis * Spongy mesophyll cells * Guard Cell * Stoma * Cuticle * Vein ### How to interpret a transverse section of a leaf? * **Lamina** * Dorsiventral nature. * **Upper Epidermis:** Straight walls, 600 to 1100 cells/sq. mm, single layered, rectangular. Trichomes: Covering: uniseriate, Multicellular, waxy, blunt tip. Glandular trichomes: Stalk unicellular, head 2 - 4 celled. Stomata: Cruciferous or unequal celled. * **Mesophyll:** Palisade: Single layered, compact cells, radialy elongated, covering 2/5th of lamina. Spongy parenchyma: 6-8 layers, loosely arranged, intercellular spaces, cluster crystrals (sphaeraphides), Micro-spheroidal crystals and vascular strands are found in upper layers. * **Lower Epidermis:** Similar to upper epidermis, stomata and numerous trichomes are 700 cells/sq.mm. * **Lamina region** * First: upper epidermal layer They are all alike except the guard cells * Second: upper palisade layer, one or more rows. * Third: spongy tissue * Fourth: lower palisade layers (may be absent) * Isobilateral leaf * Dorsiventral leaf * Homogenous mesophyll * finally the lower epidermal * **Midrib region** * Upper Epidermis * Upper Palisade * Crystal sheath * Pericyclic fiber * Xylem vessel * Phloem * Collenchyma * Lower Epidermis * **What are?** * Continuous and discontinuous palisade * Isobilateral and dorsiventral leaves ### Quantitative evaluation of drugs * Microscope is used for the quantitative evaluation of drugs and adulterated powders. * This is done by counting specific histological features such as: * stomatal number, stomatal index, vein islets and vein termination numbers, palisade ratio, * **The stomatal number:** It is the average number of stomata per square millimeter of epidermis * **Stomatal index (I):** it the ratio of the number of stomata in the unit area to the total number of epidermal cells and stomata in the same unit area multiplied by 100 * I= S* 100\ (S+E) * **Vein termination number:** is the average number of veinlet termination per square mm. this number differentiates between Coca species and also Senna species. * **Palisade ratio:** it is the average number of palisade cells beneath each epidermal cell * **Vein-islet number:** is the average number of vein islets per square mm ### Identify these tissues * Parenchyma cells * Collenchyma cells * Fiber cells (sclerenchyma) This document contains basic descriptions of different plant tissues. Images provided give visual examples of these structures.