Anatomy of Flowering Plants PDF

Anatomy of Flowering Plants © 2022, Aakash BYJU'S. All rights reserved. Key Takeaway Meristematic cells 1 2 Permanent tissue Types of meristematic tissue 3 4 Simple permanent tissue Parenchyma Complex permanent tissue Xylem Phloem © 2022, Aakash BYJU'S. All rights reserved. 5 Collenchyma Sclerenchym...

Anatomy of Flowering Plants © 2022, Aakash BYJU'S. All rights reserved. Key Takeaway Meristematic cells 1 2 Permanent tissue Types of meristematic tissue 3 4 Simple permanent tissue Parenchyma Complex permanent tissue Xylem Phloem © 2022, Aakash BYJU'S. All rights reserved. 5 Collenchyma Sclerenchyma 6 Ground tissue system 7 8 Different parts of dicot root © 2022, Aakash BYJU'S. All rights reserved. Vascular tissue system 9 10 Different parts of dicot leaf Epidermal tissue system 11 Different parts of monocot root 12 Different parts of monocot stem 13 14 Secondary growth Different parts of dicot stem 15 16 Summary © 2022, Aakash BYJU'S. All rights reserved. Different parts of monocot leaf Bark Cells and Tissues The cell is the basic structural and functional unit of all living organisms. Every living organism is made up of cells. In plants, humans and other animals, cells come together to form a tissue. Tissues come together to form an organ. Tissue is a group of cells that has a common: o Origin o Structure o Function © 2022, Aakash BYJU'S. All rights reserved. Plant tissues Meristematic tissue Permanent tissue Actively dividing cells Cells are not actively dividing Meristematic Cells Meristematic cells are actively dividing cells that are present in the growing parts of the plant body. ‘Meristos’ in Greek means ‘divided/divisible’. In plants, the growth is limited to certain specialised regions, like the tips of roots, stems and some other parts like leaves, flowers and fruits. The growth in the plants is because of the actively dividing meristematic cells. The meristems are unspecialised cells that supply new cells for growth and formation of tissue. © 2022, Aakash BYJU'S. All rights reserved. Regions of actively dividing cells such as tip of root and stem, leaves, flowers and fruits. Meristematic Cells Features Thin cell walls Features of meristematic cells Large nucleus Dividing cells No intercellular space Dense cytoplasm © 2022, Aakash BYJU'S. All rights reserved. Types of Meristematic Tissue Based on growth stage Promeristem Growth of embryonic root and shoot is due to promeristems. They are short-lived and only exist until the seed germinates into a young plant. The promeristems are responsible for embryonic growth. Primary meristem Apical meristem Intercalary meristem Root apical meristem Shoot apical meristem © 2022, Aakash BYJU'S. All rights reserved. Secondary meristem Lateral meristem Intrafascicular vascular cambium Interfascicular cambium Cork cambium Types of Meristematic Tissue Primary meristem Once the plant has grown from being a seed to a young plant, the promeristem gives rise to the primary meristems that are responsible for the growth in the next stage. Apical meristem Intercalary meristem Found at the tips of the roots and the shoots They give rise to primary tissues Present between mature tissues at the nodes of the stem Shoot apical meristem Root apical system Responsible for the growth of the roots Responsible for the elongation of internodes Occurs in grasses and regenerates parts removed by the grazing herbivores Responsible for the leaves and other aerial parts of the plants Axillary buds are formed from leftover meristematic cells. New shoots or branches or even flowers can form from these buds. © 2022, Aakash BYJU'S. All rights reserved. Types of Meristematic Tissue Secondary meristem The plant grows from a young tender plant to a thick, woody, hard tree because of secondary meristems. The increase in height or length of the tree shoots or roots is still because of primary growth or primary meristems. The increase in girth is a result of secondary meristems and the tissues that are formed are known as the secondary tissues. Lateral meristem They are cylindrical or parallel to the side of stems or branches. They are found in mature regions of roots and stems. They produce the woody axis of the plants. They are present only in dicot plants, generally absent in monocots. These meristems add girth to the branches and stems. © 2022, Aakash BYJU'S. All rights reserved. Permanent Tissue Permanent tissue consists of cells which mostly do not divide further. Simple Complex Made up of cells similar in structure and function Made up of different cell types Parenchyma Collenchyma © 2022, Aakash BYJU'S. All rights reserved. Sclerenchyma Xylem Phloem Simple Permanent Tissue Parenchyma It is derived from the Greek word ‘para’ which means ‘beside’. It is a major part of all organs of the plant. It is the most commonly found tissue. It is the most diverse and versatile cell. They have thin walls and very less or no intercellular spaces. Characteristics of parenchyma are as follows: o The cells are generally isodiametric (roughly spherical). o The cells vary in shape. Round Oval © 2022, Aakash BYJU'S. All rights reserved. Polygonal Pillar-like No/less intercellular spaces in parenchyma Simple Permanent Tissue Functions of parenchyma Photosynthesis Performs photosynthesis and cells haave abundant chloroplasts in the chlorenchyma. Chlorenchyma makes up the mesophyll of plant leaves. Storage They help in the storage of reserve food like starch. E.g., Starch in potato © 2022, Aakash BYJU'S. All rights reserved. Secretion Buoyancy Parenchymal cells line the insides of resin ducts. Aerenchyma is a modification of parenchyma. It is made up of cells with very large intercellular spaces. It helps to maintain buoyancy. Gaseous exchange Spongy mesophyll, in parenchyma have large intercellular spaces which help in exchange of gases. Simple Permanent Tissue Collenchyma Collenchyma tissue is made up of living cells. It is found either as a homogeneous layer or in patches. Collenchyma forms a layer under the epidermis in most dicotyledon stems. Cell wall is made up of: o Cellulose o Hemicellulose o Pectin There are no intercellular spaces between cells as they are filled with pectin. Epidermis Collenchyma © 2022, Aakash BYJU'S. All rights reserved. Simple Permanent Tissue Collenchyma Shapes Spherical Functions Provides mechanical support (tensile strength) Oval Provides elasticity to plant parts such as a young stem and the petiole of a leaf Polygonal Helps to resist the bending action of the wind Assimilates food when cells contain chloroplasts © 2022, Aakash BYJU'S. All rights reserved. Simple Permanent Tissue Sclerenchyma Sclerenchyma consists of cells with thick and lignified cell walls having a few or numerous pits. They are usually dead and without protoplasts. Lignin is a very complex organic substance and the second most commonly found natural organic polymer after cellulose. o It is insoluble in water. Hence, it is impermeable to water. o It is found as a thick deposition in the cell walls. Sclerenchyma provides mechanical support to organs. Cell wall is made up of: o Cellulose o Hemicellulose o Lignin They are found in stems, leaves, seed coats, fruit pulp and wall. © 2022, Aakash BYJU'S. All rights reserved. Sclerenchyma Simple Permanent Tissue Types of sclerenchyma Based on form, origin, structure and development, they are of two types. Sclereids They have highly thickened walls. They have a narrow cavity (lumen). They are of different shapes. They are commonly found in pulp of fruits like guava etc. Sclereid Thick cell wall Lumen Fibers They are elongated in shape. o Have tapering ends o Middle is bulged Cell walls are thick and have lignin deposits in them. They generally occur in groups. The cell wall has pits that help in intercellular communication. Fiber © 2022, Aakash BYJU'S. All rights reserved. Complex Permanent Tissue In photosynthesis occurs in leaves and roots absorb water as well as minerals. The plants transport water from the soil to the leaves and food synthesised in the leaves reaches all the parts of the plants through complex tissues. There is an unidirectional movement in transport of water and a bidirectional movement in transport of the synthesised food. The complex tissues are heterogenous. They are composed of different types of cells that work as a unit. © 2022, Aakash BYJU'S. All rights reserved. Complex Permanent Tissue Xylem Phloem The xylem and phloem are conducting or vascular tissues Phloem Xylem Xylem © 2022, Aakash BYJU'S. All rights reserved. Phloem Xylem It is a conducting tissue. It consists of living and non-living cells. It conducts water and minerals. It carries water from roots to all the other parts of the plant. The movement is unidirectional, i.e., from root tips to other parts of the plant. It has a thick-walled semi-rigid tube that provides mechanical support. One-way flow only Xylem - direction of movement © 2022, Aakash BYJU'S. All rights reserved. Types of Xylem Primary Protoxylem Part of the primary xylem that forms first In stem, it lies towards the center © 2022, Aakash BYJU'S. All rights reserved. Secondary It is formed during the secondary growth of plants. It is seen as annual rings. In some of the large plants, it is seen as sapwood or heartwood. Metaxylem Part of the primary xylem that forms after the protoxylem is formed In stem, it lies towards the periphery Types of Xylem Endarch The protoxylem is found inner to the metaxylem. o The protoxylem is towards the centre (adjacent to pith). o The metaxylem is towards the periphery. Endarch arrangement is seen in stem. Metaxylem Protoxylem Pith © 2022, Aakash BYJU'S. All rights reserved. T.S of dicot stem Types of Xylem Exarch The protoxylem is found outer to the metaxylem. o The protoxylem is towards the periphery. o The metaxylem is towards the centre. Exarch arrangement is seen in roots. Metaxylem Protoxylem © 2022, Aakash BYJU'S. All rights reserved. T.S of dicot root Components of Xylem Tracheids Vessel element Vessels Tracheids Xylem Xylem parenchyma Xylem fibres © 2022, Aakash BYJU'S. All rights reserved. Xylem parenchyma cell Components of Xylem Tracheids They are unicellular, elongated tube-like cells with tapering ends. Structure Function The inner layers of the cell walls have varying thickness and are lignified. The secondary cell wall helps in long-distance transport. Cells are elongated with tapering ends. The tracheids are found one above the other, separated by a cross wall/end wall that bears bordered pits. This is one of the main water transporting elements of xylem in angiosperms. The cells are dead or without protoplasm. © 2022, Aakash BYJU'S. All rights reserved. Components of Xylem Vessels Each vessel consists of broad, lignified dead cells, joined end to end forming a tubular structure. They are long, cylindrical and a characteristic features of angiosperms. Structure Function Each cell or vessel member has lignified walls and a large central cavity. The vessels are more capable for the conduction of water than tracheids. The end wall is perforated. Hence, the vessels work as a pipeline. The perforated end walls allow vessel members to be stacked end to end to form a larger conduit known as a vessel. The open-end walls of vessels provide a very efficient low resistance pathway for water movement. Vessel members © 2022, Aakash BYJU'S. All rights reserved. Components of Xylem Xylem parenchyma They are living cells having thin cell walls made up of cellulose. They store secondary metabolites like tannins and food materials like fats and starch. Radial conduction of water is performed by the ray parenchymatous cells. © 2022, Aakash BYJU'S. All rights reserved. Xylem fibres They provide strength to the tracheids and vessels. They have highly thickened walls and obliterated central lumens. These may either be septate or aseptate. Phloem It transports food (glucose produced in leaves). It is a bidirectional transport. Glucose moves up to the growing bud Bud Leaf Stem Glucose production Glucose moves down to the growing root Soil © 2022, Aakash BYJU'S. All rights reserved. Phloem Primary Secondary Protophloem Metaphloem First formed phloem Later formed phloem The primary phloem is divided into protophloem and metaphloem, based on the development. The secondary phloem forms from the vascular cambium during the secondary growth. © 2022, Aakash BYJU'S. All rights reserved. Elements of Phloem Phloem components Sieve tube elements Sieve tube Phloem parenchyma cells Sieve plate Companion cells Phloem fibres Sieve plate Sieve tube The gymnosperms have albuminous cells and sieve cells. The gymnosperms lack companion cells and sieve tubes. © 2022, Aakash BYJU'S. All rights reserved. Phloem parenchyma Companion cell Elements of Phloem Mature sieve elements Sieve elements are joined end to end with pore filled sieve plates between to make a sieve tube. They have a peripheral cytoplasm. They have a functional plasma membrane. They have a large vacuole. Tonoplast and nucleus are lost generally. © 2022, Aakash BYJU'S. All rights reserved. Narrow rim of cytoplasm Companion cell Elements of Phloem Companion cells They have a nucleus along with dense cytoplasm. They can perform metabolic and cellular functions. The companion cell is a living cell with a large elongated nucleus. This nucleus also controls the activity of the sieve tube element. Features: o They are specialised parenchymatous cells. o They are closely associated with sieve tube elements. o They are non-conducting cells. o In gymnosperms, albuminous cells are present instead of companion cells. © 2022, Aakash BYJU'S. All rights reserved. Sieve plate Sieve tube Companion cell Elements of Phloem Companion cells The longitudinal walls between companion cells and sieve tubes are connected by pit fields. The companion cells and sieve tube elements maintain close cytoplasmic connections with each other through plasmodesmata. The connection maintains the pressure gradient in sieve tubes. © 2022, Aakash BYJU'S. All rights reserved. Companion cell Sieve plate Sieve tube member Companion cell Plasmodesma Plasmodesmata Connections Sieve tube elements Elements of Phloem Phloem parenchyma They are elongated, tapering cylindrical cells. They have dense cytoplasm and a nucleus. They are absent in most monocots. They have cellulosic cell wall, pits and plasmodesmata connections between adjacent cells. They store foods like resins, latex, and mucilage. © 2022, Aakash BYJU'S. All rights reserved. Dense cytoplasm Phloem parenchyma Elements of Phloem Phloem fibres (bast fibres) They are sclerenchymatous cells. They are absent in primary phloem and are found in secondary phloem. These fibres provide mechanical support to sieve elements. They have an elongated, unbranched structure. They have a very thick cell wall with pointed, needle-like apices. At maturity, they have loose protoplasm and become dead. Phloem fibres of jute, flax and hemp are commercially useful. © 2022, Aakash BYJU'S. All rights reserved. Tissue Systems Types of tissue systems based on location and structure Epidermal Epidermal cells Ground Stomata Vascular Epidermal appendages Trichomes © 2022, Aakash BYJU'S. All rights reserved. Hair Epidermal Tissue System Epidermal cells They are parenchymatous. They have a little cytoplasm lining the cell wall. They have a large vacuole. Cells are lined by cuticle. o It is a waxy thick layer present outside the epidermis. o It prevents the loss of water. o It is absent in roots. © 2022, Aakash BYJU'S. All rights reserved. Cuticle Nucleus Cell wall Vacuole Epidermal Tissue System Stomata They are small pores in the epidermis of leaves. They regulate the transpiration and gaseous exchange. Stomatal apparatus consists of Stomata Guard cells Stomatal pore Guard cells © 2022, Aakash BYJU'S. All rights reserved. Subsidiary cells Epidermal Tissue System Guard cells of stomata They are bean-shaped or dumb-bell shaped and possess chloroplasts. They enclose the stomatal pore. They have a thin outer wall. They have a highly thickened inner wall. They regulate the opening and closing of stomata. Subsidiary cell Thin outer wall Chloroplast © 2022, Aakash BYJU'S. All rights reserved. Subsidiary cells of stomata They are specialised epidermal cells. They surround the guard cells. Thick inner wall Stomatal pore Guard cell Epidermal Tissue System Epidermal appendages Root hair They are unicellular elongations of the epidermal cells. They help in the absorption of water and minerals. © 2022, Aakash BYJU'S. All rights reserved. Trichomes They are epidermal hairs on the stem. They are usually multicellular in the shoot system. They are branched or unbranched. They are soft or stiff. They may be secretory. They prevent the water loss due to transpiration. Ground Tissue System It includes all the tissues except epidermis and vascular bundles. It usually consists of simple tissues. Parenchyma © 2022, Aakash BYJU'S. All rights reserved. Collenchyma Sclerenchyma Ground Tissue System Parenchymatous tissue is found in stem and roots. Cortex: In plants, tissue of unspecialised cells lying between the epidermis (surface cells) and the vascular tissues is cortex. Pericycle: It is a thin layer of thick-walled parenchymatous cells just below the endodermis. Pith: It is composed of undifferentiated parenchyma cells, which function in storage of nutrients, found in young plants. Medullary rays: Medullary rays are strips of parenchyma present between vascular bundles of dicot stem. They separate xylem and phloem bundles. © 2022, Aakash BYJU'S. All rights reserved. Ground Tissue System In leaves Mesophyll: It is made of thin-walled-chloroplast containing cells. It lies between the upper and the lower epidermis of the leaf. Palisade mesophyll Mesophyll Spongy mesophyll © 2022, Aakash BYJU'S. All rights reserved. Vascular Tissue System Phloem and xylem together form the vascular bundles or vascular system. In monocots They have closed vascular bundles. o The cambium is absent. o The secondary tissues are not formed. © 2022, Aakash BYJU'S. All rights reserved. In dicots They have open vascular bundles. o The cambium is present in between the phloem and xylem. o The cambial activity gives rise to the secondary xylem and phloem tissues. Vascular Tissue System Based on arrangement, vascular bundles are of 2 types Radial Conjoint Alternate arrangement along different radii Found in roots Arranged together along the same radius Found in stems and leaves Phloem usually on the outer side of xylem Phloem Xylem Cambium Xylem Phloem Closed © 2022, Aakash BYJU'S. All rights reserved. Open Different Parts of Dicot Root The dicot roots have a taproot system. o A taproot system is made of a central, large root that is known as the primary root. o The primary root is larger in diameter than the lateral roots. Transverse section of dicot root Epidermal tissue Ground tissue Vascular tissue © 2022, Aakash BYJU'S. All rights reserved. T.S of dicot root Different Parts of Dicot Root a) Epidermis Also known as epiblema/rhizodermis Protective in function Some epidermal cells protrude to form root hairs b) Cortex It is a multilayered thin-walled structure, made up of a mass of parenchymatous cells with intercellular spaces between them. The innermost layer is of barrel-shaped cells without any intercellular space is called endodermis. c) Casparian strips The tangential and radial walls of endodermal cells have suberin deposition in the form of strips known as casparian strips. © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Dicot Root d) Pericycle and conjunctive tissue A few layers of thick-walled parenchymatous cells known as pericycles (beneath the endodermis) help in the formation of lateral roots and secondary growth by forming cambium. Parenchymatous cells that lie between the xylem and the phloem are known as conjunctive tissue. e) Pith Pith is small and inconspicuous, made up of parenchymal cells. f) Vascular tissues 2-4 phloem and xylem patches are present. g) Stele All tissues on inner side of endodermis constitute the stele. © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Monocot Root  They have a fibrous root system.  The monocot roots and dicot roots are similar in their internal structure except for few differences. Epidermal tissue Ground tissue Vascular tissue Section of monocot root © 2022, Aakash BYJU'S. All rights reserved. Difference Between Monocot and Dicot Root Features Dicot root Monocot root Xylem and Phloem Diarch to tetrarch: There are 2 to 4 xylem and phloem bundles. Polyarch: There are more than 6 bundles of xylem and phloem. Pith It is small or inconspicuous. It is large and well developed. Secondary growth From the pericycle of dicot roots, vascular cambium is formed at a later part of plant life that helps in the secondary growth. From the pericycle of monocot roots, there is no vascular cambium formation. Therefore, there is no secondary growth. © 2022, Aakash BYJU'S. All rights reserved. Difference Between Monocot and Dicot Root Dicot root Monocot root Root hair Epiblema Epidermis Cortex Endodermis Phloem Pericycle Xylem Pith © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Dicot Leaf   It has reticulate venation. It has dorsal and ventral surfaces. Cuticle Adaxial epidermis Epidermal tissue system       The epidermis on the upper surface of a leaf is known as adaxial epidermis. The epidermis on the lower surface of a leaf is known as abaxial epidermis. The conspicuous cuticle is present on epidermis. The stomata is present on the epidermis of the leaf. The abaxial epidermis has more number of stomata, hence it is known as hypostomatic leaf. Guard cells in dicot leaves are bean shaped. © 2022, Aakash BYJU'S. All rights reserved. Abaxial epidermis Stoma T.S of dicot leaf Different Parts of Dicot Leaf Ground tissue system  The tissue between the upper and the lower epidermis is known as the mesophyll.  The mesophyll cells that possess chlorophyll carry out photosynthesis. Mesophyll Palisade parenchyma Spongy parenchyma  Present near the adaxial surface.   The elongated cells are arranged vertically and are parallel to each other. Present below palisade parenchyma and extend to lower epidermis.  Cells are oval/round and loosely arranged.  The intercellular spaces are filled with air cavities. © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Dicot Leaf Vascular bundles  The vascular tissues are present in midrib and veins.  The size of vascular bundles varies due to variation in thickness of veins.  The vascular bundles are surrounded by thick-walled bundle sheath cells.  The xylem is on the upper side and the phloem is on the lower side. Dicot leaves are known as dorsiventral leaves as the upper and lower regions have distinct features. © 2022, Aakash BYJU'S. All rights reserved. Transverse Section of Dicot Leaf Bundle sheath Xylem Phloem Adaxial epidermis Palisade mesophyll Air cavity Spongy mesophyll Substomatal cavity Abaxial epidermis Stoma © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Monocot Leaf  It has parallel venation.  The monocot leaves are also known as isobilateral leaves as both of its surfaces are similar. Epidermal tissue system   Equal number of stomata are present in the epidermis on both sides of the leaf, hence it is known as an amphistomatic leaf. Stomatal pore Guard cells in monocot leaves are dumbbell shaped. Stomata Guard cells © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Monocot Leaf Epidermal tissue system   The bulliform cells are large, empty, and colourless cells present in adaxial epidermis that absorb water and become turgid when the leaf surface is exposed. They help in rolling and unrolling of leaves due to change/variations in turgidity.  The mesophyll is present between upper and lower epidermis.  The mesophyll is not differentiated into palisade and spongy parenchyma.  They consist of chlorenchyma cells. © 2022, Aakash BYJU'S. All rights reserved. Bulliform cells Adaxial epidermis Xylem Phloem Abaxial epidermis T.S of monocot leaf showing bulliform cells Different Parts of Monocot Leaf Vascular tissue system   The vascular bundles are surrounded by bundle sheath cells. The xylem is on the upper side and the phloem is on the lower side. T.S of monocot leaf Cuticle Adaxial epidermis Substomatal chamber Mesophyll Xylem Phloem Abaxial epidermis Stoma © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Monocot Stem Epidermal tissue system  The epidermis is made up of monolayered. parenchymatous cells.  The hypodermis is made up of sclerenchyma cells. Ground tissue system  The ground tissue is large and parenchymatous. Epidermis Vascular bundles Ground tissue T.S of monocot stem © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Monocot Stem Vascular tissue system  The vascular bundles are scattered in ground tissue.  The peripheral vascular bundles are generally smaller than the centrally located vascular bundles.  The pith and pericycle are absent.  The vascular bundles are conjoint and closed due to the absence of cambium.  There is no secondary growth.  The sclerenchymatous bundle sheath surrounds the vascular bundles.  The phloem parenchyma is absent.  Vascular bundles have water containing cavities. © 2022, Aakash BYJU'S. All rights reserved. Anatomy of Monocot Stem Monocot stem Epidermis Hypodermis Epidermis Vascular bundles Ground tissue Phloem Metaxylem Protoxylem Bundle sheath © 2022, Aakash BYJU'S. All rights reserved. Hypodermis Scattered vascular bundles in ground tissue Different Parts of Dicot Stem Epidermis   It is the outermost layer that is protective in function. It comprises of 1. Trichomes: They are unbranched multicellular hair that arise from the epidermal layer. 2. Stomata: They are present on leaves, young green stems, and other green parts of the plants. They usually help in gas exchange. 3. Cuticle: It is a thin, waxy layer that protects the plants. It prevents the loss of water from the epidermal cells. Epidermal hair Cuticle Epidermis Epidermis (dicot stem) © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Dicot Stem Outer-Hypodermis  Cortex Has collenchyma cells which provide mechanical strength. Middle-General cortex   Has parenchymal cells. The parenchymatous cells are thin-walled and provide cushioning. They are round with intercellular spaces. Inner-Endodermis  It is also known as starch sheath because the cells store starch. © 2022, Aakash BYJU'S. All rights reserved. Layers of cortex Different Parts of Dicot Stem Pericycle  Present below the starch sheath (endodermis)  Made of sclerenchyma cells  Found as semilunar patches Pericycle © 2022, Aakash BYJU'S. All rights reserved. Different Parts of Dicot Stem Vascular bundles  They are arranged like a ring.  They are open, conjoint and endarch.  Conjoint: Xylem and phloem are arranged in the same radius.  Open: Cambium is present between the xylem and phloem.  Endarch: Protoxylem lies towards the centre or the pith, and the metaxylem lies towards the periphery of the stem.  Parenchymal cells between the vascular bundles are called medullary rays. © 2022, Aakash BYJU'S. All rights reserved. Vascular bundles T.S of dicot stem Secondary Growth Promeristems During embryonic growth, the promeristems drive the growth. Secondary meristems Meristems that take part in secondary growth. Embryonic growth Secondary growth Primary meristems As seeds germinate, primary meristem divides and plant grows to form primary tissues. It drives the increase in girth of the stem/root with help of the secondary lateral meristems. It is only seen in dicots. Primary growth Primary tissue Apical meristems form shoots and roots. The tissues formed are primary tissues. E.g. Primary vascular bundles. © 2022, Aakash BYJU'S. All rights reserved. Secondary tissue E.g. Secondary xylem and phloem. Secondary Growth Vascular cambium Intrafascicular cambium  Interfascicular cambium The patchy or non-continuous cambium between primary xylem and primary phloem is known as the intrafascicular cambium.  The cells of medullary rays, adjoining these intrafascicular cambium, become meristematic and form the interfascicular cambium. Primary phloem Herbaceous dicot stem Primary xylem Interfascicular cambium Intrafascicular cambium © 2022, Aakash BYJU'S. All rights reserved. Dicot stem with cambial ring Secondary Growth Cambial ring  The interfascicular cambium and the intrafascicular cambium together form the cambial ring.  The cambial ring becomes active and cuts off cells on both the sides.  On the outer side or towards the periphery, it leads to the formation of secondary phloem.  Towards the inner side or (pith) it gives rise to the secondary xylem.  The secondary xylem layers formed inside accumulate inwards. The different primary xylems from different vascular bundles merge together.  Since the monocots lack cambium unlike dicots, secondary growth that results in increased girth is not observed in them. © 2022, Aakash BYJU'S. All rights reserved. Secondary Growth Secondary medullary rays The cambium forms a narrow band of parenchyma, which passes through the secondary xylem and the secondary phloem in the radial directions forming the secondary medullary rays. Secondary medullary rays Primary phloem Primary xylem Secondary xylem Secondary phloem Cambium ring Young dicot stem © 2022, Aakash BYJU'S. All rights reserved. Mature dicot stem Secondary Growth Cambium Vascular cambium Interfascicular cambium Cork cambium Intrafascicular cambium  Due to the secondary growth of the vascular cambiums, the epidermis bursts.  The epidermis is replaced by a protective layer known as the cork, which is formed by the cork cambium.  Cork cambiums are the meristematic tissues formed in the cortex. © 2022, Aakash BYJU'S. All rights reserved. Secondary Growth Cork development Epidermis Cortex Damaged epidermis Cork cambium Cortex Damaged epidermis Cork cambium Cortex Damaged epidermis Cork cambium Cortex © 2022, Aakash BYJU'S. All rights reserved. As the secondary growth occurs due to vascular cambial activity, the epidermis eventually breaks. The damaged epidermis is replaced by a new protective layer. A new layer of secondary meristem or cambium called cork cambium or phellogen appears. The cork cambium expands. Cork cambium cells are narrow, thinwalled and rectangular. Secondary Growth Damaged epidermis Cork Cork cambium Cortex The cork layer is formed towards the periphery. Damaged epidermis Cork Cork cambium Secondary cortex Cortex © 2022, Aakash BYJU'S. All rights reserved. Secondary cortex is formed towards the inner side of cork cambium. Secondary Growth Cork development  The outer cells differentiate into the cork or the phellem.  The inner cells differentiate into the secondary cortex or the phelloderm.  The cork is impervious to water due to the suberin deposition in the cell wall of the cork cells. Damaged epidermis Cork Cork cambium Secondary cortex (Phelloderm) Cortex © 2022, Aakash BYJU'S. All rights reserved. Secondary Growth Cork Cork cambium Secondary cortex Cortex  Together, the three layers (phellem, phellogen and phelloderm) form the periderm. © 2022, Aakash BYJU'S. All rights reserved. Periderm Damaged epidermis Secondary Growth Root  The vascular cambium is formed during secondary growth.  It starts off as a complete and continuous wavy ring that later becomes circular.  The vascular cambium originates from the tissue located just below the phloem bundles, a portion of pericycle tissue, above the protoxylem.  Further development occurs as in dicot stem. Epidermis Cortex Vascular cambium Secondary phloem Primary xylem Secondary xylem © 2022, Aakash BYJU'S. All rights reserved. Epidermis/periderm Cortex Annual ring Mature dicot root Bark  Layers beyond vascular cambium are termed as the bark.  It is a non-technical term.  It includes the following: o Secondary phloem o Phelloderm o Phellogen Periderm o Phellem (Cork) © 2022, Aakash BYJU'S. All rights reserved. Cork cambial activity Bark Due to cork cambial activity, pressure builds up on phellem or cork These outer layers die and slough off Bark Bark Early or soft bark Late or hard bark Formed early in the season Formed in the end of the season © 2022, Aakash BYJU'S. All rights reserved. Bark Cambium Lenticels  The lens-shaped openings that are known as lenticels are created when the epidermis ruptures.  They exchange gases between the outer atmosphere and the internal tissue.  They are found as raised circular, oval, or elongated parts on the surface of the bark.  Phellogen or cork cambium in this region gives rise to complementary cells instead of cork or phellem.  Complementary cells are closely arranged parenchyma cells. © 2022, Aakash BYJU'S. All rights reserved. Lenticel Broken epidermis Complementary (parenchyma) cells Secondary cortex (Phelloderm) Annual Ring Dendrochronology  When cutting a dicot tree, the tree trunk has a characteristic ring-like pattern.  Each ring actually signifies one year of the tree's growth.  Counting all the rings, one can tell the age of the tree.  This science is known as dendrochronology. Formation of annual rings 1 light band + 1 dark band = 1 annual ring  The tree produces an annual ring that represents its growth during the year.  The light and dark bands are due to the different seasons. © 2022, Aakash BYJU'S. All rights reserved. Spring Wood & Autumn Wood Spring wood Autumn wood  Also known as the early wood  Also known as the late wood  Formed when nutrients are easy to access  Develops in autumn when nutrients are scarce in cold  Xylary elements grow quickly and are large in number  Fewer xylary elements  Xylary elements have wider cavities  Xylary elements have narrow vessels  Cambium is very active  Cambium is less active © 2022, Aakash BYJU'S. All rights reserved. Sapwood & Heartwood Sapwood Heartwood  Sapwood is the light brown secondary xylem  Heartwood is the dark brown secondary xylem  Present in the peripheral region of the secondary xylem  It gives mechanical support and is hard and durable It has deposits of tannins, resins, oils, gums, aromatic substances, and essential oils It is resistant to microorganisms and insects     Living tissues conduct water and minerals Present in young trees/plants © 2022, Aakash BYJU'S. All rights reserved.  It is a dead tissue that has highly lignified walls They do not conduct water  Present in older trees  Summary Cells (basic building blocks of all living organisms) Tissues (groups of cells) Meristematic tissue (actively dividing cells) Promeristem (young meristematic cells in early embryonic stage) Primary meristems (responsible for primary growth) Secondary meristems (responsible for girth increment) Intercalary meristems (responsible for growth of internodes) Apical Meristems (found at the root and shoot tips) Lateral Meristems (add girth to stem) Interfascicular cambium (formed between two vascular bundles) © 2022, Aakash BYJU'S. All rights reserved. Intrafascicular cambium (present between xylem and phloem of the vascular bundle) Cork cambium (produces secondary tissue that replaces the epidermis in roots and stems) Summary Cells (basic building blocks of all living organisms) Tissues (groups of cells) Permanent tissue (Do not divide actively) Complex (made up of different types of cells) Simple (made up of one type of cells) Parenchyma (soft tissue found in softer parts of leaf, fruits, etc.) Collenchyma (consist of cells thickened at corners and provide mechanical support) Fibres (elongated cells that provide support to plants) © 2022, Aakash BYJU'S. All rights reserved. Xylem Phloem Sclerenchyma (dead mechanical tissue) Sclereids (spherical, oval or cylindrical, highly thickened dead cells) Summary Permanent tissues Complex tissues Xylem The xylem transports water unidirectionally. © 2022, Aakash BYJU'S. All rights reserved. Simple tissues Phloem The phloem transports food material bidirectionally. Summary Types of xylem Components of xylem Development of xylem Primary xylem It develops during the primary growth. Secondary xylem It develops during the secondary growth. Tracheids They are elongated tube-like cells with tapering ends. They are main water transporting elements. Vessels They are long cylindrical, lignified dead cells. Xylem parenchyma They are living cells with a cell wall made of cellulose. Xylem fibres They provide strength to tracheids and vessels. Protoxylem It is the first formed xylem consisting of small cells. Metaxylem © 2022, Aakash BYJU'S. All rights reserved. It is formed after the protoxylem and has a larger lumen. Summary Types of phloem Elements of phloem Primary It develops during the primary growth. Secondary It develops during the secondary growth. Sieve tubes They are long longitudinal cells associated with companion cells. Companion cell It has a large nucleus and is present in angiosperms. Phloem parenchyma It is an elongated, taper ended cell that stores food in angiosperms. Phloem fibres/Bast fibres They are unbranched, needle-like cells with thick cell walls. © 2022, Aakash BYJU'S. All rights reserved. Summary Tissue systems Ground tissue system It includes all tissues except epidermis and vascular bundles. © 2022, Aakash BYJU'S. All rights reserved. Epidermal tissue system It includes stomata, epidermis, and epidermal appendages. It includes cuticles and trichomes depending on presence in the leaf or root. Vascular tissue system It includes phloem and xylem. Based on arrangement of vascular bundles, it is classified as radial and conjoint. Summary Vascular Bundles Radial Conjoint Xylem and phloem alternate radially Found in roots Xylem Phloem Xylem and phloem are joined together Found in stem and leaf Phloem on the outer side Open Closed Cambium is present between xylem and phloem No cambium between xylem and phloem Phloem Cambium Xylem © 2022, Aakash BYJU'S. All rights reserved. Summary Dicot root Monocot root Root hair Epiblema Epidermis Cortex Endodermis Phloem Pericycle Xylem Pith © 2022, Aakash BYJU'S. All rights reserved. Summary Epidermis Vascular Bundles Vascular bundle Ground tissue Epidermis Cortex T.S of monocot stem © 2022, Aakash BYJU'S. All rights reserved. T.S of dicot stem Summary Bulliform cells Adaxial epidermis Cuticle Xylem Abaxial epidermis Adaxial epidermis Phloem Abaxial epidermis T.S of monocot leaf showing bulliform cells © 2022, Aakash BYJU'S. All rights reserved. Stoma T.S of dicot leaf Summary Intrastelar secondary growth in dicot stem Secondary medullary rays Primary phloem Primary xylem Secondary xylem Secondary phloem Cambium ring Young dicot stem © 2022, Aakash BYJU'S. All rights reserved. Mature dicot stem Summary Extrastelar secondary growth in dicot stem Cork Cork cambium Secondary cortex Cortex Mature dicot stem The three layers (phellem, phellogen and phelloderm) form the periderm. © 2022, Aakash BYJU'S. All rights reserved. Periderm Damaged epidermis