long cells • Possess tapering end walls • Cell wall are thick and lignified • Possess only pitted thickenings • Provide only mechanical support Difference Between Sieve Cells and Sieve Tubes Sieve cells Sieve tubes • Have no companion cells • The sieve areas do not form sieve plates • The sieve areas are not well differentiated • They are elongated cells and are quite long with tapering end walls • The sieve are smaller and numerous • Found in Pteridophytes and Gymnosperms • Have companion cells • The sieve areas are confined to sieve plates • The sieve areas are well differentiated • They consist of vertical cells placed one above the other forming long tubes connected at the walls by sieve pores • The sieve pores are longer and fewer • Found in Angiosperms . Epidermal tissue system (derived from protoderm) . Ground tissue system (derived from ground meristem) . Vascular tissue system (derived from procambium) Histology (Greek.
histos – web, logos – science) It is the study of tissues, their composition, and structure as observed with the help of microscope. Table . : Types and characteristics of tissue systems S.No. Types/ Characters Epidermal tissue system Ground or fundamental tissue system Vascular or conduction tissue system .
Formation Forms the outermost covering protoderm Forms the ground meristem Forms the procambial bundles . Components epidermal cells, stomata and epidermal outgrowths Simple permanent tissues – Parenchyma and Collenchyma Xylem and Phloem . Functions Protection of plant body; absorption of water in roots; gas exchange for photosynthesis and respiration; transpiration in shoots Gives mechanical support to the organs; prepares and stores food in leaf and stem Conducts water and food; gives mechanical strength . Epidermal Tissue System Introduction Epidermal tissue system is the outer most covering of plants.
It is in direct contact with external environment. It consists of epidermis derived from protoderm.Epidermis is derived from two Greek words, namely ‘Epi’ and ‘Derma’. ‘Epi’ means upon and ‘Derma’ means skin . It is made up of single layer of parenchyma cells which are arranged compactly without