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Uploaded byVasantaKahalkar
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Equisetum

This document summarizes the external and internal morphology of Equisetum (horsetail). It describes that Equisetum has underground stems called rhizomes that produce both sterile and fertile aerial branches. The sterile branches are green and photosynthetic while the fertile branches are short-lived and bear spores. The stems have scale-like leaves arranged in whorls and fibrous roots occur at rhizome nodes. Internally, the stem has ridges and grooves with photosynthetic tissue under ridges and air canals under grooves. Vascular bundles alternate with the canals and a pith cavity is in the center.

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External Morphology of Equisetum Dr. Vasanta I. Kahalkar Department of Botany M. G. Arts, Science & Late N. P. Commerce College, Armori
External Morphology of Equisetum • Division – Sphenophyta • Class – Sphenopsida • Order – Equisitales • Family – Equisitaceae • Genus – Equisetum • The sporophyte, i.e., the plant body is well differentiated into – stem, leaves and roots.
The stem: Stem is underground, horizontal and much branched, which often penetrates more than a meter into the soil. The rhoizome is jointed and provided with nodes and internodes. It gives off two types of branches – sterile and fertile branches. Sterile branches are green in colour, persistent and have a whorl of lateral branches at each node. Sterile branches are vegetative in function. Fertile branches are generally unbranched, short lived and bears a single strobilus at its tip.
A whorls of lateral branches is present at each node of the vegetative shoot.These branches are of the following two types. 1. Branches of Unlimited growth- They are further branches like the main vegetative shoot and are differentiated into nodes and internodes. 2. Branches of limited growth- They are also differentiated into nodes and internodes like vegetative shoot but remain unbranched. • Leaves – Leaves are small, slender, scale-like. They are arranged in whorls at each node. They are fused at the base and free at the tip which forms a teeth like structure. They form a cup like structure at the base of the internodes. • Roots - Roots are slender, much branched and adventitious (fibrous type). They occur only at the nodes of the rhizomes.
T.S. of Root: • The root in transverse section shows – epidermis, cortex and stele. 1. Outermost layer is epidermis, from which arise many root hairs. 2. Cortex is thick and multi-layeredand differentiated into an outer sclernchymatous and an iiner paranchymatous region. 3. Outer zone of cortex consists of 3 to 4-celled thick exodermis. 4. Inner zone is parenchymatous with many intercellular spaces. 5. Endodermis is two-layered. He cells of the outer endodermal layer are larger and have casparian bands but those of the inner endodermal layer are smaller and without casparian bands. 6. Pericycle is absent. 7. Stele is a protostele, which is diarch or tetrarch. A large metaxylem tracheid is present in the centre of the stele and protoxylem strands lie around it. 8. Phloem is present in between the protoxylem strands.
Internal Structure of Stem Equisetum
• It is wavy in outline because of the presence of ridges and grooves. • Outermost layer is the epidermis, cells of which have a deposit of silica in their outer and lateral walls. • Due to the presence of silica, the stem appears hard and rough to touch. • The continuity of epidermis is broken by sunken stomata present in each groove. In each sunken stoma, the guard cells are covered completely by subsidiary cells, thus giving the appearance of two sets of guard cells. • Below the epidermis is present a-well-developed cortex. • Just below each ridge is present a large patch of sclerenchyma, which is mechanical in function. Sclerenchyma is also present below the grooves in between chlorenchyma. • Inner to be sclerenchyma is present chloren-chymatous tissue below each ridge. It is photosynthetic in function. • Rest of the cortex is parenchymatous and many layered. • Just below each groove is present a large air canal in the parenchymatous cortex. It is known as vallecular canal. • Innermost layer of cortex is the endodermis, the cells of which contains casparian strips.
• Below the endodermis is present a single-layered pericycle. • Vascular bundles are present below the ridges, i.e., alternate to the vallecular canals of the cortex. They are present in the ring. • The number of vascular bundles and vallecular canals is equal to the number of ridges and grooves, respectively. • Stele is of ectophloic siphonostelic type. • Each vascular bundle is conjoint, collateral, closed, and consists of xylem, phloem and some parenchyma. • In each Vascular bundle is present a water- containing cavity or canal called carinal canal. • Xylem is ‘V’- shaped. • Protoxylem is endarch lying opposite to carinal cavity. It consists of annular and spiral tracheids. • Two strands of metaxylem are present. • Phloem is present in between two strands of metaxylem and made up of phloem parenchyma and sieve tubes. • Pith is present in the form of pith cavity, located in the centre of the aerial shoot.
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