Roots And Stems Botax PDF

Endodermis: 8mm; A single layer of Roots cells forming the innermost boundary of the cortex. General Description:...

Endodermis: 8mm; A single layer of Roots cells forming the innermost boundary of the cortex. General Description: Early Metaxylem: 12-15 mm ; Primarily involved in the transport of water and nutrients, forming part of Roots are vital plant structures that primarily the vascular system. grow into or towards the soil. Roots do not develop leaves and rarely Old zone: Includes “Zone of elongation” and produce buds. “Zone of Cell Differentation”. Fully developed The growing apex of roots is typically covered, which serves to protect this sensitive region. Late metaxylem: 100 mm The main functions of roots include Exodermis: 40 mm absorption of water and nutrients, storage of Epidermis energy reserves, and providing support for the plant. Histology of Roots Gross Anatomy and Physiology of Roots Monocot Roots Root Hairs Monocot roots display various features based on their surrounding environment, which can range from Root hairs are minute and simple structures aquatic, semi-aquatic, mesophytic (survive neither found as elongations of the root epidermis. dry or wet environment), and xerophytic (survive in Located at the back of the root cap and appear deserts or tundra) conditions. Notable features as slender tubes. include: The primary purpose of root hairs is to significantly increase the absorbing surface Epidermis: Characterized by the presence of area of roots, thereby facilitating the uptake of root hairs which increase surface area for water and nutrients from the soil. absorption. Hypodermis: Comprising 2 to 3 layers of cells Root Cap with extremely thickened walls. Endodermis: Contains a 1 layer of cells The root cap is a sheath-like covering infiltered with suberin and lignin. Protects the delicate growth point of the root. It acts as a mechanical aid, aiding the root in - Contains Caspanian strip ensuring pushing through the soil as it grows. selective uptake of water and Release carbon dioxide that forms carbonic nutrients. Also, ensures it enters the acid that helps in dissolution of substances. It xylem only. can dissolve rocks and other minerals. Comprised of cells that are continually Cortex: broad zone of parenchyma cells sloughed off as they experience wear from the soil. Pericambium: Consists of 1-2 layers of cells with extremely thin walls that facilitate growth Generative Tissues and repair. Radio fibro-vascular bundles: alternating The root is composed of various generative tissues, xylem and phloem which include: Xylem: cells, trachea, and woof fibers Plerome: Responsible for the development of Phloem- cells and sieve tubes fibroblast tissue. Periblem: Produces the apex of the root. Medulla (Pith): Contains parenchyma cells Dermatogen: Gives rise to the epidermis of rich in starch. Located at center most portion. the root. Calptrogen: Produces the root cap. Dicot Roots Median Longitudinal Section of Roots In contrast, dicot roots often exhibit a tetrarch structure, characterized by four xylem strands In a median longitudinal section of roots, various alternating with four phloem strands. This zones can be observed: arrangement is vital, offering an unlimited power of growth. Key features include: Tip Zone: Contains the root cap and apical meristem, proendodermis (later on become PRIMARY GROWTH mature endodermis layer) critical for growth. Young Zone: This includes the zone of Epidermis: Often cutinized outer walls, maturity and zone of cell division, where new providing protection against desiccation. cells are actively produced. Hypodermis Primary cortex: Usually small intracellular Cortex: Layers that serve as storage spaces and transport.  Endodermis: Contains a pericycle that gives Apoplast Pathway: Involves water moving rise to lateral roots. through the interconnected plant cell walls, bypassing the cytoplasm initially. Innermost layer of cells of cortex Lenticularly thickened radial walls Classification of Roots Pericambium: Known as an active growth 1-2 Roots can be classified according to various criteria, layers that may produce side roots. including their form and duration. Pith: Composed of small zone of parenchyma cells. According to Form Radial-fibrovascular bundle: Contains four phloem patches; alternating with many xylem Primary Roots: Direct downward growth from arms. the seed, also known as the main or tap root. Secondary Roots: Develop latter growth, Xylem: composed of spiral trachea, covered with soil and supplied with moisture. internal are few pitted vessels Follows hydrotropism and geotropism. Phloem: Bast fibers Primary and Secondary: SECONDARY GROWTH When it comes to primary and secondary roots, they can either be fibrous or fleshy. Intrafascicular cambium: Cells dividing by tangential walls Fibrous Roots: Small diameter and scattered Inner curve of phloem patches growth. Characterized by many thin roots with About 6 weeks little to no central tap root. Pericambium: Fleshy Roots: Larger in diameter and have Single cell flattened layer multiple forms, often storing significant Starts to cut off on its inner side a amounts of food and water. quantity of secondary xylem Pushes out patches bast fibers 1. Fusiform/spindle – shaped like radish Xylem fills up the patches between arms or parnsnip. Cork Cambium: 2. Napiform/turnip – globular and Outer layer of pericambium abruptly becoming slender. Cork tissue on its outer face Terminates in a conical tap root. Filled with air 3. Conical root – largest diameter at the Interfascicular cambium: base then tapering. Ex: carrots Inner of pericambium Joins the intrafascicular cambium to form Anomalous Roots: Irregular or unusual a continuous cambium ring. habits. Subserving other purposed from the normal like anchorage and water and mineral Root Tubercles absorption. Ex: Sweet potatoes Adventitious Roots: Occuring in abnormal Root tubercles are nodule-like swellings places on the plants commonly found on plant families such as Fabaceae (legumes; mungo) and Myricaceae Katakataka (Kalanchoe pinnata Fam. (sweet gales). CRASSULACEAE) These structures are often a result of the interaction with bacteria, specifically Epiphytic/ Aerial Roots: commonly seen in Pseudomonas radicicola, which attaches to root tropical forests. hairs and forms branching tubes. Inside the cortex, these bacteria multiply, leading It never reaches the soil. to the formation of aggregate nodes that house Cling to the bark of trees for anchorage nitrogen-fixing bacteria essential for the plant's Absorb nutrients and moisture from nutrient cycle. The bacteria remain within the host the air. Ex: Orchids until their death, at which point they break down into soluble nitrogenous substances that benefit Haustoria/ Parasitic plant roots: penetrate the plant. the bark or plants. Lodgment and absorb nutritious juices of sap. Ex: mistletoe Water Movement in Roots Aerating: Rising above the ground. Lives in swamps. Ex: mangroves Starts through the root hairs going to the root Contractile: Expands radially and contracting xylem to stem xylem. longitudinally Propagative Roots: Develop adventitious Roots facilitate the movement of water largely through buds that produce shoots above ground. Ex: two pathways: Quaking aspen Storage Roots: Tuberous roots. It can be Symplast Pathway: Involves water classified as stems or roots. Modified portion movement through the cytoplasm of cells via of roots that swells function as food and water plasmodesmata. storage. According to Duration Stem Elongation and Development Annual Plants: 1 season or 1 year; Dermatogen: Layer responsible for forming Characterized by roots lacking - no stored the epidermis. nourishment, such as tiger grass. Periblem: Develops cortex. Biennial Plants: Develop aerial organs in the Plerome: Forms the fibro-vascular elements first year. Large amount of reserve food and pith. materials is stored in roots for the next season. Ex: carrots Physiological Functions of Stems Perennial Plants: Roots that allow the plant to live indefinitely. Ex: Buttress roots Support: Provides structural support to leaves and reproductive structures. Conduction: Facilitates the movement of water and dissolved minerals (crude sap), and organic matter (elaborated sap). New living tissues: apical and lateral meristems. STEMS Histology of Stems Difference Between Roots and Stems Typical Herbaceous Monocot Stem Roots: Epidermis: Cutinized outer walls. o Have a descending axis Hypodermis: Generally collenchymatic. o Growth occurs at the sub-apical Cortex: Contains an endodermis. region Fibro-vascular Bundles: Large central zone o Lack chlorophyll of parenchyma matrix scattered within the o Exhibit irregular branching patterns stem. o No appendages (addition) present Xylem: Surrounds the phloem entirely. Not o Generally possess a simple structure surrounded by anything. Stems: o Feature an ascending axis Typical Woody Monocot Stem o Growth occurs at the apical region o Sometimes contain chlorophyll Epidermis: Single-layered with walls strongly o Branches are arranged in a cutinized cells. mathematically regular pattern Cortex: Composed 10-12 layers of thick- o Form appendages walled parenchyma cells. o Exhibit a more defined structure Endodermis: Contains strongly suberized brownish walls. General Types of Stems Sclerenchymatous Cylinder Sheath: Contains fibers and underdeveloped vascular Caulescent: Stems rise above the ground and bundles. are apparent. Central matrix: Usually scattered and Acaulescent: Stems are not visible above irregular. It is strongly thickened parenchyma ground. cells. Stem Classification by Structure Dicot Stem Exogenous Stems: Epidermis: Cutinized with hairs. o Common in gymnosperms and Cortex: Three layers: dicotyledons o Characterized by the presence of 1. Exoxortex or Outer: Cells are thin walled; contains chloroplasts. cambium 2. Mediocortex: Indurated walls; extreme o Stronger pliability and strength. Endogenous Stems: 3. Endocortex or Inner: Very broad zone of o Typical of most monocots thin- and thick-walled parenchyma cells. o Characterized by an absence of cambium Endodermis: Typically, indistinguishable with o Hollow and weaker the cortex. Pericambium: Not distinguishable Gross Anatomy of Stems Pith: Central area composed of parenchyma. Fibrovascular Bundle: Open collateral type Nodes: Points on the stem where appendages arranged in concentric circles with primary like leaves are attached. medullary rays between the bundles. Internodes: area between two nodes. Buds: Underdeveloped shoots which can be terminal or axillary. Growth of Perennial Stem Cut through phloem and the medullary rays are spindle shaped. Periblem Development Wood Structure Epidermis: Develops from dermatogen, eventually peeling off. Later, entirely absent. Wood: Portion of woody exogenous plant axis Cork Tissues or Periderm: Formed by cork inside of the cambium line. Yearly lose cambium (phellogen). protoplasmic content and become filled with Cork cambium or Phellogen extractive, resinous, and coloring materials. Phelloderm: Zone of thin-walled chloroplast- Annual Rings: Formed by seasonal changes bearing cells. Cut off by the cork cambium. and provide approximate measures of tree Cortex: May undergo modification into: age. mucilage cells, tannin receptacles, crystal Seasonal Growth Patterns: cells, and spiral cells. o Spring: Active growth, producing large ducts with little woody fibers. Loosely Plerome Development arranged. o Summer and Autumn: Decreased Fibrovascular Bundles: Include primary and growth, resulting in small ducts with secondary medullary rays. tightly packed mechanical woody o Protophloem: Hard bast fibers that is fibers. Densely arranged. long and tenacious. o Secondary Phloem: Soft bast fibers Section of Wood: with phloem cells and sieve tubes. o Cambium: Regulates secondary 1. Cross phloem and outer secondary xylem 2. Tangential – right angle to the radium development. Adds depth to 3. Radial – through the center along a radius. medullary rays to allow movement of substances in between of Types of Wood fibrovascular bundles. o Secondary Xylem: Composed of Alburnum (Sapwood): Outer whitish layers wood fibers, pitted vessels, and tracheids. containing living cells functioning in vegetative o Protoxylem: Spiral trachea processes. Duramen (Heartwood): Inner dead layers that provide structural support. Bark Structure Types of Stems: According to Duration Bark: All portions of a woody exogenous plant axis outside the cambium line. Brown in color. Zones of Bark: Annual: Complete life cycle in one year. o Outer bark (cork) – dead cork cells Biennial: Complete life cycle in two years. filled with air Perennial: Live for multiple years. o Middle bark (cortical parenchyma) – has suberized cork cells that includes Types of Stems: According to Stem Growth protoplasm. o Inner bark (phloem) Ascending: Grows obliquely upward. Reclining: Initially erect, bends as it grows. Histology of Bark Procumbent: Lies wholly/ flat on the ground. Decumbent: stem trails on the ground with Transverse or Cross Section upward-curving apex. Repent: Creeping along the ground, rooting at Cork: Rectangular cells. nodes. Common for stolons (runner). Ex: Cork Cambium/Phellogen: Delicate cells Strawberries with protoplasmic content undergoing division. Types of Stems: According to Stem Modification Cortex: Composed of outer brownish collenchyma and inner broader zone of Twining: Elongation with circular motion of elongated cortical parenchyma. Stones are young internodes. imbedded for bark strength. Tendriliform: Thread-like modification sensitive to contact of a side-branch. Ex: Radial Section Squash Spines/Thorns: Adaptation for defense Medullary Rays: 15 to 25 cells in height. through thickening and hardening of a branch. Composed of crystal fibers of calcium oxalate Ex: Roses and bast fibers which appears elongated and Aerial Tuberolic: One or more enlarged taper ended. internodes above ground for food storage. Similar to tuberous. Tangential Section Subterranean: Underground food storage centers (tubers, corms, bulbs, rhizomes).  Phyllode: Leaf-like flattened branch structures occurring in reduced leaves. Cactoid: Reduced condensed branches or stems and swollen for water and food storage. No regular leaves. Ex: Cactus Types of Stems: According to Location Above Ground Stems: o Twining o Climbing/ scandent: grows upward by attachment. Aerial rootlets, tendtrils, or petioles. o Spine/ Thorn o Stolon o Culm: Jointed stem of grasses. Ex: sugar cane and bamboos. o Scapes: Rising from the ground but only bears flowers. Ex: dandelions o Prickles: Outgrowths for protection. Ex: Roses o Herbaceous: Soft and easily broken. Commonly seen in monocots. o Undershrub/ suffruticose: Woody at the base but herbaceous at young stem. Small in size. o Shrubby/ fruticose: Woody stem larger than undershrub. Freely branching near the ground. o Trunk: Woody main stem of the tree. Underground Stems: o Rhizomes: Creeping underground and capable of sending up shoots and roots. They are more or less scaly and bears terminal buds. Perennial. Ex: Ginger o Tubers: Excessively thickened tips for food storage. Borne at the end of slender creeping branch. Annual. Ex: Potato o Corms: Thickened, solid, irregular shapes. Annual. o Bulbs: Very short with scaly coverings. Round. Tunicated: Completely covered by broad scales. Ex: Onions Scaly: Narrow imbricated scales. Ex: Turnips