PLANT TISSUE AND ANATOMY

PLANT TISSUE AND ANATOMY

 

Anatomy: Anatomy is the study of internal structure of an organism.

Tissue: A group of cells having essentially a common function and origin is called as tissue

Meristematic tissue: It is a group of young cells. These are living cells with the ability to divide into the regions where they are present.

Primary meristem or Promeristem: Primordial meristem or pro-meristem is also called as embryonic meristem. Usually occupying the very minute area at the tip of root and shoot.

Primary meristem: Primary meristem originates from the primordial meristem and occurs in the plant body from the beginning, at the root and shoot apices.

Secondary meristem: Secondary meristematic tissues develop from living permanent tissues during later stages of plant growth; hence are called as secondary meristems. e.g. Interfascicular cambium and cork cambium

Apical meristem: Apical meristem is produced from promeristem and forms growing point of apices of the root, shoot and their lateral branches.

Intercalary meristem: Intercalary meristematic tissue is present in the top or base area of the node. Their activity is mainly seen in monocots.

Lateral meristem: Lateral meristem is present along the sides of the central axis of organs. It takes part in increasing girth of stem or root.

Protoderm: Young growing region of the plant has Protoderm that forms protective covering like epidermis around the various organs

Procambium:  Procambium is involved in developing primary vascular tissue.

Ground meristems: Other structures like cortex, endodermis, pericycle medullar rays, pith are formed from the region of Ground meristem.

Permanent tissues: This is a group of cells which have lost the capacity of division and acquired permanent size, shape and functions.

Simple tissues: These are made up of only one type of cells carrying similar functions.

Parenchyma:  These are thin-walled, isodiametric, round, oval to polygonal or elongated in shape. These cells store water and food, provide buoyancy and perform photosynthesis.

Collenchyma: It is a simple permanent tissue made up of living cells. The cell wall is cellulosic but shows uneven deposition of cellulose and pectin especially at corners. They provide mechanical strength to the young stem of plant and petiole of the leaf.

Sclerenchyma: It is simple permanent tissue made up of compactly arranged thick-walled dead cells. The cells are living at the time of production but at maturity, they become dead due to uniform deposition of lignin. They provide mechanical strength.

Complex tissues: This tissue is heterogeneous comprising of more than one type of cells and all function as a single unit.

Xylem: It is a dead complex tissue. Components of xylem are tracheids, vessels, xylem parenchyma and xylem fibres. The xylem also provides mechanical strength and conducts water and minerals.                 

Tracheids: Tracheids are elongated, tubular and dead cells. The ends are oblique and tapering.

Vessels: Vessels are longer than tracheids with perforated or dissolved ends and formed by the union of several vessels end to end. These are involved in the conduction of water and minerals.

Xylem parenchyma:   Cells are small associated with tracheids and vessels. The function is to store food (starch) and sometimes tannins.

Xylem fibres: Xylem fibres are sclerenchymatous cells and serve mainly mechanical support. These are called wood fibres. These are also elongated, narrow and spindle-shaped. Cells are tapering at both the ends and their walls are lignified.

Phloem: This is a living tissue. It is also called as bast. Phloem is responsible for conduction of organic food material from source (leaf generally) to a sink (other plant parts).

Sieve tubes: Sieve tubes are a long tubular conducting channel of phloem. These are placed end to end with bulging at end walls.

Sieve plates: The sieve plates connect protoplast of adjacent sieve tube cells.

Sieve cells: Sieve cells are found in lower plants like pteridophytes and gymnosperms.

Companion cell: Companion cells are narrow elongated and living. They regulate the function of Sieve tube through simple pits.

Phloem parenchyma: Phloem parenchyma cells are living, elongated found associated with sieve tube and companion cells. The chief function is to store food, latex, resins, mucilage, etc.

Phloem fibres: Sclerenchymatous dead tissues present in secondary phloem Thes cell are with lignified wall and provide mechanical strength. Also known as bast fibres. These used in making ropes and rough clothes.

Protophleom:  The first formed primary phloem consist of narrow sieve tube

Metaphloem: The later formed primary phloem consists of bigger sieve tubes.

Epidermis: Outermost protective cell layer made up of compactly arranged cells without intercellular space.

Cuticle: The outer side of the epidermis is often covered with a waxy thick layer called the cuticle

Root hair: These are unicellular elongated hair-like structure present on the epidermis or root and involved in the absorption of sap from the soil.

Trichomes: In stem, epidermal hairs are called trichomes. These are generally multicellular, branched or unbranched, stiff or soft or even secretory.   

                                 

Stoma: Small gateway or pores in the epidermal cells are called as a stoma.

Stomatal apparatus: The stoma, guard cell and the surrounding subsidiary cells are together called the stomatal apparatus.

Guard cells: Specialized epidermal cells adjacent to a stoma that regulate the opening and closing of stomata. They possess chloroplasts and guard cells in dicots are kidney-shaped and in monocot are dumbbell shape.       

                                            

Subsidiary cell: Few epidermal cells in the vicinity of the guard cell becomes specialized in their position and  size and are known as subsidiary cells.          

                                            

The ground tissues: All tissues except epidermis and vascular bundles constitute the ground tissues.

Hypodermis: The layer present below the epidermis. In monocot, it is made up of sclerenchyma whereas in dicot it is made up of collenchyma

Vascular tissues system: These are the distinct patches of the complex tissue viz. Xylem and phloem.

Radial vascular bundles: When both the complex tissue is situated separately on the separate radius as a separate bundle. This is a common feature of roots.

Conjoint vascular bundles: The complex tissue is collectively present as neighbours of each    other    on the same radius in the form of xylem inside and phloem outside.

Open vascular bundles: If the cambium is present in vascular bundles it is called open type vascular bundles. It is responsible for secondary growth in the stem of gymnosperms and dicot.

                                                                                                                                    

Closed vascular bundles: Cambium is absent in such plants. These plants do not show secondary growth like monocots.

Bicollateral vascular bundle: When phloem is present in a vascular bundle on both the sides of xylem and intervening cambium tissue, it is called the bi-collateral vascular bundle. e,g Cucurbitaceae.

Concentric vascular tissues: When one vascular tissue is completely encircling the other, it is called a concentric vascular bundle.

Leptocentric: Phloem encircled by xylem.

Hadrocentric: Xylem encircled by phloem.

Amphicribal: Xylem encircled by phloem On both the faces.

Amphivasal: Phloem encircled by xylem on both faces.

Primary growth: The vertical growth of the roots and stems in length with the help of apical meristem is called as primary growth.

Intrafascicular cambium: The cambium present between the primary xylem and primary phloem of a vascular bundle is called intrafascicular cambium. It is a primary meristem.

Interfascicular cambium: The cells of medullary rays adjoining intrafascicular cambium becomes meristematic and called interfascicular cambium.

Cambial ring: The intrafascicular and interfascicular cambium join to form a cambial ring which is responsible for secondary growth.

Dedifferentiation: With the onset of favourable season meristematic cells of interfascicular cambium becomes active. The ray parenchyma cells, both fusiform initials and ray initial become meristematic. This is known as dedifferentiation.

Wood:  The wood is a secondary xylem.

Spring wood: During favourable conditions, spring wood (early wood) is formed   which has broader xylem bands, lighter colour, tracheids with thin wall and wide lumen, fibres are less in number, low density.

Autumn wood: During unfavourable season autumn wood (late wood) is formed which has narrow xylem band, darker in colour, the lumen is narrow and walls are thick with abundant fibres are present of high density. 

                                                      

Tyloses: Tracheary elements of the heartwood are plugged by in-growth of adjacent parenchyma cells i.e. tyloses.

Heartwood: The Inner non-functional, durable part which is resistant to pathogens is called duramen or heartwood.

Sapwood: Outer light, functional part of secondary xylem, cells are living, no deposition, lighter and less durable, more susceptible to pathogens.

Cork Cambium: Phellogen (cork cambium) develops in extrastelar region of stem. The outer cortical cells of cortex become meristematic and produce a layer of thin-walled, rectangular cells. These cells cut off new cells on both sides.

Phellem: Phellem cork cell is produced by cork cambium towards the outer side.

Phelloderm: Phelloderm or secondary cortex is formed by cork cambium towards the inner side.

Periderm: Phellogen, phellem and phelloderm together form periderm.

Bark: To all cell types found external to vascular cambium including secondary phloem. The bark of early season is soft and of the late season is hard.

Lenticels: Lenticels are aerating pores present as (raised scars) the surface of the bark. These are portions of periderm, where phellogen activity is more, lenticels are means for gaseous and water vapour exchange.

Anomalous secondary: Accessory cambium development in plants like Dracena, Agave, Palms and root of sweet potato show presence of secondary growth. This is called anomalous secondary growth.

Epiblema: An outermost single layer of cell in roots without cuticle is Epiblema.

Root hair: Some of the cells of epiblema shows unicellular extensions which help in absorption of sap.

Cortex: Next to epidermis several layers of parenchymatous cell constitute cortex.

Exodermis: After the death of epiblema outer layer of cortex becomes cutinized and is called exodermis.

Endodermis: The the innermost layer of the cortex is called endodermis. The cells are barrel-shaped and their radial walls show deposition band of suberin which forms Casparian strip or deposition band.

Passage cells: Near the protoxylem, there are unthickened passages cells with allows entry of water.

Stele of dicot root: It consists of 2 to 6 radial vascular bundles present in parenchymatous mass.

Exarch:  Protoxylem is located towards pericycle in roots This is termed as exarch condition.

Conjunction tissues: A parenchymatous connective tissue or conjunction tissue is present between xylem and phloem.

Pith: The central part of a stele or vascular cylinder is called Pith.

Starch sheath: In dicot stem endodermal cell contains plenty of starch grains It is called a starch sheath.

Stele: The central core of tissues differentiated into pericycle, vascular bundles and pith is called a stele.

Hard bast: The pericycle in sunflower is multilayered to form hard bast.

Vascular bundle of dicot stem: Conjoint collateral and open. It shows ring arrangement.

Vascular Bundle of monocot stem: Numerous vascular bundles are surrounded by a Sclerenchymatous bundle sheath vascular bundle are conjoint collateral and closed.

Endarch: In stem, metaxylem faces the pericycle this is called endarch.

Mesophyll: Is differentiated into palisade and spongy tissue in dicot leaf.

Palisade parenchyma: Palisade parenchyma is present below the upper epidermis and consists of closely packed elongated cells. The cells contain abundant chloroplasts and help in photosynthesis.

Spongy parenchyma: Spongy parenchyma is present below palisade tissue and consists of loosely arranged irregularly shaped cells with intercellular spaces. The spongy parenchyma cells contain chloroplast and are in contact with the atmosphere through stomata.   

                              

The vascular system of leaf: Is made up of a number of vascular bundles of varying size depending upon the venation. Each one is surrounded by a thin layer of parenchymatous cells called Bundle sheath.