Samacheer Class 11 Bio Botany - Tissue and Tissue System

Sclereids are dead cells with highly thickened and lignified cell walls that provide mechanical support and protection to plant tissues. These cells are characterized by their isodiametric shape, meaning they are roughly equal in all dimensions, though some sclereids may be somewhat elongated. The cell wall of sclereids is extremely thick due to extensive lignification, which is the deposition of lignin in the cell wall matrix, making them very hard and rigid. The lumen, or the internal cavity of the cell, is much reduced in size due to the thick cell wall deposition. Sclereids contain numerous pits in their cell walls, which are small channels that allow for limited communication between adjacent cells. These pits may be simple, appearing as small openings, or branched, forming a network of interconnected channels. Sclereids are found in various plant tissues including seed coats, fruit walls, and leaf tissues, where they provide protection and structural support. They are also found in the pulp of fruits like pears and guavas, giving these fruits their characteristic gritty texture.

Sieve tubes are long tube-like conducting elements in the phloem. These are formed from a series of cells called sieve tube elements. The sieve tube elements are arranged one above the other and form vertical sieve tube. The end wall contains a number of pores and it looks like a sieve. So it is called as sieve plate. The sieve elements show nacreous thickenings on their lateral walls. They may possess simple or compound sieve plates.
The function of sieve tubes are believed to be controlled by campanion cells In mature sieve tube, Nucleus is absent. It contains a lining layer of cytoplasm. A special protein (P. Protein = Phloem Protein) called slime body is seen in it. In mature sieve tubes, the pores in the sieve plate are blocked by a substance called callose (callose plug). The conduction of food material takes lace through cytoplasmic strands. Sieve tubes occur only in Angiosperms.

Characters
Dicot root
Monocot root
1. Pericycle
Gives rise to lateral roots, phellogen and a part of vascular cambium
Gives rise to lateral roots only.
2. Vascular tissue
Usually limited number of xylem and phloem strips.
Usually more number of xylem and phloem strips,
3. Conjunctive tissue
Parenchymatous; Its cells are differentiated into vascular cambium.
Mostly sclerenchymatous but sometimes parenchymatous. It is never differentiated in to vascular cambium.
4. Cambium
It appears as a secondary meristem at the time of secondary growth.
It is altogether absent.
5. Xylem
Usually tetrach
Usually poly arch
6. Pith
Absent
Present at the centre

The dicot stem and monocot stem show several important anatomical differences that reflect their different growth patterns and structural organization. In the hypodermis, dicot stems have collenchymatous tissue providing flexible support, while monocot stems have sclerenchymatous tissue providing rigid support. The ground tissue in dicot stems is clearly differentiated into distinct regions including the cortex, endodermis, pericycle, and pith, each with specific functions, whereas in monocot stems the ground tissue is not differentiated and exists as a continuous undifferentiated mass of parenchyma cells. A starch sheath is present in dicot stems but absent in monocot stems. Medullary rays, which are radial bands of parenchyma extending from the pith to the cortex, are present in dicot stems but absent in monocot stems. The vascular bundles in dicot stems are collateral and open, meaning the cambium between xylem and phloem remains active, and they are arranged in a single ring or cylinder around the stem. In contrast, monocot stems have collateral and closed vascular bundles with no cambium, and these bundles are scattered throughout the ground tissue rather than arranged in a ring. Finally, dicot stems undergo secondary growth due to the activity of the vascular cambium, allowing them to increase in diameter, while monocot stems typically do not undergo secondary growth and maintain a relatively constant diameter throughout their life.

The correct option is b) False – True – False – True. Let's analyze each statement: I) The innermost layer of the cortex is known as the pericycle. This statement is False. The innermost layer of the cortex is the endodermis, which is distinct from the pericycle. The pericycle is located just inside the endodermis, forming the outermost layer of the stele. II) Suberin, lignin, and some other carbohydrates are present as strips in the radial and inner tangential walls of the endodermis. This statement is True. These strips are known as Casparian strips, which are characteristic features of the endodermis and play a crucial role in regulating water and solute movement into the vascular cylinder. III) Endodermis is known as the outermost layer of the stele. This statement is False. The endodermis is the innermost layer of the cortex, while the pericycle is considered the outermost layer of the stele. IV) In Angiosperms, the pericycle gives rise to lateral roots. This statement is True. The pericycle is a meristematic tissue in angiosperms and is responsible for the initiation and development of lateral roots.

Sclerenchyma is the primary tissue found in these fruits that provides them with their characteristic gritty texture. Sclerenchyma cells are dead at maturity and possess thick, lignified secondary cell walls, which provide mechanical support and protection to the plant. In fruits like pear and guava, these cells are often found as sclereids, also known as stone cells, which contribute to the hard and gritty consistency. The fruits identified are: A – Pear fruit, B – Strawberry, and C – Guava. In pear and guava, the grittiness is due to the presence of abundant sclereids. In strawberry, while the fleshy part is soft, the small 'seeds' on the surface are actually achenes, which are fruits themselves, and their hard outer layer contains sclerenchymatous tissue.

The statement regarding collenchyma cell walls needs to be completed with the correct substances. Collenchyma cell walls primarily contain cellulose and pectin. Therefore, if A and B are the blanks, the correct option would be one that identifies these components. Collenchyma cells are characterized by unevenly thickened cell walls, especially at the corners, and these thickenings are rich in cellulose, hemicellulose, and pectin. These substances provide flexibility and mechanical support to young growing parts of the plant without hindering their growth. The provided answer 'C. C → E → A → D → B VII. From the given choose the correct answer – Regarding Assertion & Reason' seems to be a misplaced or incomplete response to a different question, not directly answering the collenchyma cell wall composition. A correct answer for the collenchyma statement would be: Collenchyma cell walls contain A (cellulose) and B (pectin).

• The organisation of cells and different kinds of tissues is understood.
• It is studied by means of dissection and microscopic examination.
• The organisation of cells and different kinds of tissues is understood by the study of anatomy
• The anatomical structure of different organs of plants can be compared
• The anatomical knowledge play an important role in taxonomical studies too.

The pulp of pear is stony and gritty due to the presence of brachysclereids, which are short, isodiametric sclerenchyma cells distributed throughout the mesocarp tissue. These cells provide mechanical strength and create the characteristic hard, granular texture when the fruit is eaten. In contrast, the seed coat of Pisum sativum (garden pea) is bony and shiny because it contains osteosclereids, which are elongated, bone-like sclerenchyma cells that form a thick, protective layer. The osteosclereids are tightly packed and highly lignified, giving the seed coat its hard, smooth, and glossy appearance. Both types of sclerenchyma cells serve protective and supportive functions, but their different shapes, sizes, and arrangements result in the distinct textural and visual characteristics of these plant structures.

Centrarch and Mesarch are two types of xylem arrangements based on the position of protoxylem and metaxylem in the vascular bundle. In the Centrarch condition, the protoxylem lies in the centre of the vascular bundle and is surrounded by metaxylem on all sides. This arrangement is found in plants like Selaginella species where typically only one vascular bundle is developed. In contrast, the Mesarch condition occurs when the protoxylem is centrally located but metaxylem develops both towards the centre and towards the periphery, creating a more complex arrangement. This condition is observed in plants like Ophioglossum species where many vascular bundles are developed. The key distinction lies in the spatial relationship between the primary xylem elements and the secondary xylem tissues, which reflects different patterns of vascular development in these plant groups.

Trichoblasts and trichomes are two distinct types of epidermal structures with different locations and functions. Trichoblasts are specialized cells found in the root epidermis, which is composed of a single layer of parenchyma cells of varying sizes. The root hairs are extensions of the smaller epidermal cells known as trichoblasts, and they function primarily in water and mineral absorption from the soil. Trichomes, on the other hand, are unicellular or multicellular appendages that originate from the epidermal cells of stems and leaves. These structures can be branched or unbranched, and they may be glandular or non-glandular in nature. Trichomes serve multiple protective functions including reducing water loss, protecting against herbivores and UV radiation, and aiding in the dispersal of fruits and seeds. While trichoblasts are root-specific absorption structures, trichomes are diverse epidermal outgrowths on aerial parts that provide protection and facilitate seed dispersal.

Exarch and Endarch conditions describe the spatial arrangement of protoxylem and metaxylem within the vascular bundle, and they are characteristic of different plant organs. In the Exarch condition, the protoxylem lies towards the periphery or outer region of the vascular bundle while the metaxylem is positioned towards the centre. This arrangement is typically observed in root anatomy, where the exarch condition is the normal pattern of xylem development. In contrast, the Endarch condition occurs when the protoxylem is located towards the centre and the metaxylem develops towards the periphery or outer region of the vascular bundle. This arrangement is characteristic of stem anatomy in most plants. The distinction between these two conditions reflects the different developmental patterns and functional requirements of roots and stems, with the exarch condition in roots allowing for radial growth and the endarch condition in stems facilitating secondary growth and structural support.

• In Monoeoi stem, Xylem vessels occur in the form of letter ‘ Y’. The upper two arms of has two metaxylem vessels and at the base on or two protoxylem vessels occur.
• At maturity, the lowes, basal protoxylem disintegrates and form a cavity known as Protoxylem lacuna.

Eustele and Atactostele are two different patterns of vascular bundle arrangement in plant stems. In the Eustele condition, the vascular bundles are arranged in the form of a ring or cylinder around the central pith region. This organized arrangement is characteristic of dicot stems, such as in sunflower plants, where the bundles are clearly defined and regularly positioned. In contrast, the Atactostele condition is characterized by vascular bundles that are scattered irregularly throughout the ground tissue without any definite pattern or arrangement. This scattered distribution is typical of monocot stems, such as in maize plants, where numerous small vascular bundles are distributed throughout the stem cross-section. The Eustele arrangement in dicots allows for secondary growth and the formation of annual rings, while the Atactostele arrangement in monocots does not permit secondary growth. These different vascular patterns reflect the structural and developmental differences between dicots and monocots.

Bast fibres are strong, cellulosic fibres that are derived from the phloem tissue or the outer bark region of certain plants. These natural fibres are obtained from plants such as jute, kenaf, flax, and hemp, where they provide mechanical support to the plant body. The fibres associated with the phloem are sometimes referred to as pericyclic fibres, though they are actually phloem fibres in origin. Bast fibres are commercially important and are widely used in the textile industry for producing fabrics, ropes, and other materials. Their strength and durability make them valuable natural resources for various industrial applications. The presence of these fibres in the phloem region contributes to the structural integrity of the plant stem and bark.

• The apparently inactive centre in the root anatomy, located between root cap and differentiating cells of the root.
• It is the site of hormone synthesis and also the ultimate source of all meristematic cells of the meristem.

Xylary fibres and extra xylary fibres (phloem fibres or bast fibres) are two types of fibres found in plants with different origins and associations. Xylary fibres are associated with the secondary xylem tissue and are derived from the vascular cambium during secondary growth. These fibres are found in many woody plants and contribute to the strength and rigidity of the wood. Examples include fibres found in teak wood. Extra xylary fibres, also known as bast fibres or phloem fibres, are derived from the phloem tissue or the outer bark region of plants and are not associated with the xylem. These fibres are obtained from plants such as jute, kenaf, flax, and hemp. The key distinction is that xylary fibres originate from the vascular cambium and are part of the secondary xylem, while bast fibres originate from the phloem and are located outside the xylem tissue. Both types provide mechanical support, but their different origins and locations reflect their distinct developmental pathways and functions in the plant body.

Bulliform cells are specialized, large, thin-walled cells found in the upper epidermis of grasses and some other plants. These cells are also known as motor cells due to their functional role in leaf movement. Bulliform cells are larger than the surrounding epidermal cells and have thinner cell walls, which allows them to change shape more readily. These cells are instrumental in the rolling and unrolling of grass leaves in response to changes in weather conditions and water availability. When water is abundant, the bulliform cells become turgid and the leaf remains unrolled and flat, allowing maximum exposure to sunlight for photosynthesis. During dry conditions or water stress, the bulliform cells lose water and become flaccid, causing the leaf to roll inward, which reduces the exposed surface area and minimizes water loss through transpiration. This mechanism is an important xerophytic adaptation that helps grasses survive in arid and semi-arid environments.

Protoxylem and metaxylem are two components of primary xylem, while protophloem and metaphloem are two components of primary phloem, all derived from the procambium during primary growth. The protoxylem consists of the first-formed xylem elements that differentiate from the procambium, while the metaxylem comprises the later-formed xylem elements that develop after the protoxylem. The protoxylem typically has narrower vessels and tracheids with less rigid walls compared to the metaxylem. Similarly, the protophloem consists of the first-formed phloem elements including sieve tubes and companion cells that differentiate from the procambium, while the metaphloem comprises the later-formed phloem elements that develop subsequently. The protophloem often degenerates or becomes non-functional as the plant matures and the metaphloem takes over the primary transport function. The key distinction is that protoxylem and metaxylem are successive components of the primary xylem tissue responsible for water and mineral transport, whereas protophloem and metaphloem are successive components of the primary phloem tissue responsible for organic nutrient transport. Both pairs represent the temporal sequence of vascular tissue development during primary growth.

The bundle sheath in the stem differs significantly from that in the leaf in terms of composition and location. In the stem, the bundle sheath is the tissue that surrounds and encloses the vascular bundle, providing protection to the vascular tissues within. In monocot stems, the bundle sheath is sclerenchymatous in nature, meaning it consists of thick-walled, lignified cells that provide mechanical support and protection. In contrast, the bundle sheath in leaves, whether dicot or monocot, is parenchymatous, composed of thin-walled living cells. This leaf bundle sheath is also referred to as border parenchyma and serves a protective function while allowing for metabolic activities. The key distinction lies in the cell type composition: sclerenchymatous in stems for structural rigidity, and parenchymatous in leaves for both protection and physiological functions including photosynthesis and translocation of photosynthates.

Guard cells and subsidiary cells are both specialized epidermal cells associated with stomata, but they have distinct structures and functions. Guard cells are the two cells that directly flank the stomatal pore. In dicot leaves, they are kidney-shaped, while in monocot leaves they are dumbbell-shaped. Guard cells contain chloroplasts, which enable them to perform photosynthesis and generate the osmotic potential necessary for their movement. The primary function of guard cells is to regulate the opening and closing of the stoma through changes in turgor pressure, thereby controlling gas exchange and water loss. Subsidiary cells, in contrast, are specialized epidermal cells that are distinct from the ordinary epidermal cells and surround the guard cells. These subsidiary cells lack chloroplasts, distinguishing them from guard cells. Although subsidiary cells do not directly control stomatal opening and closing, they play an important supporting role by assisting guard cells in the process of stomatal regulation. The presence of subsidiary cells helps maintain the structural integrity around the stoma and may facilitate the movement of guard cells.

Radial and collateral vascular bundles differ fundamentally in the spatial arrangement of their xylem and phloem tissues. In radial vascular bundles, the xylem and phloem are arranged on different radii, alternating with one another around a central axis. This means that if you view a cross-section, the xylem and phloem tissues are positioned at different points around the circumference, separated by parenchymatous tissue. Radial bundles are typically found in roots of both monocots and dicots, where this arrangement provides structural support and efficient water conduction from the periphery toward the center. In collateral vascular bundles, the phloem and xylem lie on the same radius, arranged one above the other along the same radial line. Specifically, the phloem is positioned above (toward the outer surface) and the xylem is positioned below (toward the inner surface). This arrangement is referred to as conjoint and collateral. Collateral bundles are characteristic of stem anatomy in both monocots and dicots, where this configuration facilitates efficient translocation of both water and photosynthates in the vertical direction.

• Plants adapted to grow in salty environmental conditions are known as Halophytes
• The secretion of ions by the salt glands, present in the leaves is the best mechanism to regulate the salt content of plant shoots.
• Eg. Mangrove Plants-Avicennia

• Main function is to provide mechanical strength.
• Grittiness in the pulp of fruits like Guava, the presence of Pear, Pyrus etc is due to the presence of Sclerenchyma tissue.
• Provide rough and stiffness to seed coats nuts etc.
• Give various types of commercially useful fibres. Eg. Jute, hemp, cotton.

A hydathode is a specialized type of epidermal pore found in higher plants that functions in the process of guttation, the release of excess water from leaves. Structurally, hydathodes are modified stomata, though they differ from typical stomata in their function and location. Hydathodes are usually located at the leaf tips or margins, particularly at the leaf teeth or serrations, where they facilitate the exudation of water droplets. These structures are especially prominent in submerged aquatic plants such as Ranunculus fluitans, where they help regulate water balance in the plant body. Hydathodes are also found in many herbaceous land plants, particularly those growing in conditions of high humidity or high soil moisture where excess water uptake occurs. Unlike stomata, which primarily regulate gas exchange, hydathodes function mainly in water secretion. The water exuded through hydathodes often contains dissolved minerals and organic compounds, and this process is driven by root pressure rather than by the opening and closing mechanisms characteristic of guard cells in stomata.

• In some leaves the upper and lower epidermis remain multilayered.
• The outer most layer has cuticle.
• In Nerium these multilayers and the culicle help to reduce the rate of transpiration.
• In Ficus the upper epidermal layer contain cystoliths made up of calcium carbonate crystals.
• These are plants that grow in dry climatic conditions and these are the Anatomical adaptations seen in xerophytic plants.

• In the Dicot stem, Dicot root and Monocot root the central part is made up of ground tissue known as pith.
• Usually, starch, fatty substances, tannin, phenol, calcium oxalate crystals are stored in the pith.
• Function: storage

• The theory was proposed by A. Schmidt (1924)
• There are two zones of tissues are found in apical meristem.
• Tunica-It is the peripheral zone of shoot apex that forms epidermis.
• Corpus – It is the inner zone of shoot apex that forms cortex and stele of the shoot.

• The Korper Kappe theory was proposed by schuepp.
• This theory is equivalent to Tunica corpus theory of shoot apex.
• The two divisions are distinguished by the type of T division.
• Korper is characterised by inverted T divisions
• Kappe is characterised by straight T divisions.

Xylary fibres are specialized sclerenchymatous cells that are associated with the secondary xylem tissue, providing mechanical strength and support to the plant. These fibres are derived from the vascular cambium during secondary growth. There are four main types of xylary fibres, each with distinct characteristics: Libriform fibres are typically long, narrow, and possess simple pits, which are unbordered. Their secondary walls are heavily lignified, making them very strong. Fibre tracheids are generally shorter than libriform fibres and have moderate wall thickening. Their pits can be either simple or bordered, showing an intermediate structure between tracheids and libriform fibres. Septate fibres are unique because their lumen is divided into distinct chambers by thin, unlignified septa, which are cross-walls. An example of a plant with septate fibres is Teak. Lastly, Gelatinous fibres are characterized by having less lignin and a higher proportion of cellulose in their cell walls, often forming a thick, unlignified inner layer known as the G-layer. These fibres are highly flexible and are often found in tension wood.

Xylem vessels are specialized conducting cells with perforated end walls that allow for the passage of water and mineral solutions. The perforation plate is the area of the end wall where the cell wall material has been dissolved, creating openings for water transport. Single perforation plates occur when the entire end wall is dissolved, resulting in a single large pore or opening. This type of perforation plate is found in plants such as Mangifera, where the complete dissolution of the end wall creates an unobstructed passage for water movement between adjacent vessel elements. Multiple perforation plates, in contrast, contain many smaller pores rather than a single large opening. In this case, the end wall is perforated by numerous small holes, creating a sieve-like appearance. Multiple perforation plates are found in plants such as Liriodendron. The presence of multiple smaller perforations may provide greater structural support to the end wall compared to a single large perforation, while still allowing efficient water transport. The type of perforation plate present in a plant species reflects adaptations to its specific environmental conditions and water transport requirements.

The Apical Cell Theory, proposed by Carl Wilhelm von Nägeli, suggests that a single, large, tetrahedral apical cell is responsible for the growth and differentiation of all tissues in the shoot and root apices of certain plants. This theory posits that this single apical initial cell, typically tetrahedral in shape, undergoes divisions to produce all the primary tissues. In the context of root meristems, for example, the apical initial is believed to produce the root cap from one side through its divisions, while the remaining three sides give rise to the epidermis, cortex, and vascular tissue. This theory is particularly observed in lower plants, specifically vascular cryptogams such as ferns and bryophytes, where a prominent single apical cell can be clearly identified at the growing tips. However, in higher plants (gymnosperms and angiosperms), the apical meristem is generally composed of a group of initial cells rather than a single apical cell, which is explained by the Histogen Theory or Tunica-Corpus Theory.

Prosenchyma and chlorenchyma are two specialized types of parenchyma tissue that differ in their structure and function. Prosenchyma consists of parenchyma cells that have become elongated, pointed at their ends, and slightly thick-walled. These cells are adapted to provide mechanical support to the plant body while retaining the living, metabolically active nature of parenchyma. Prosenchyma cells are often found in regions where both support and flexibility are required. Chlorenchyma, on the other hand, refers to parenchyma cells that contain chlorophyll and are therefore capable of photosynthesis. Chlorenchyma is the primary photosynthetic tissue in leaves and is exemplified by the mesophyll of leaves. In dicot leaves, the mesophyll is further differentiated into two distinct types of chlorenchyma: palisade tissue and spongy tissue. Palisade tissue consists of elongated, columnar cells arranged perpendicular to the leaf surface, optimized for maximum light absorption. Spongy tissue, located beneath the palisade tissue, consists of loosely arranged cells with large intercellular spaces that facilitate gas exchange and allow for the diffusion of carbon dioxide to photosynthetic cells. This differentiation of mesophyll into palisade and spongy tissues in dicot leaves represents an adaptation for efficient photosynthesis.

Fibres and sclereids are both sclerenchymatous cells that provide mechanical support to plants, but they differ in their morphology, distribution, and origin. Fibres are long, slender cells with narrow, elongated bodies and pointed ends, giving them a needle-like appearance. They typically occur in bundles or strands, where multiple fibres are grouped together to provide collective mechanical strength. Fibres are commonly unbranched and are derived directly from meristematic tissue during primary growth. In contrast, sclereids are short, broad cells with a more compact, isodiametric or irregular shape. They may be branched or unbranched and typically occur individually or in small groups scattered throughout the tissue rather than in organized bundles. Sclereids develop from secondary sclerosis of parenchyma cells, meaning they originate from the thickening and lignification of existing parenchyma cells rather than from meristematic tissue. Both fibres and sclereids have thick, lignified cell walls that provide rigidity and strength, but their different morphologies and distributions suit them to different mechanical support functions within the plant body.

The quiescent centre concept was proposed by Clowes in 1961 to explain the organization and activity of the root apical meristem. The quiescent centre is a region of apparently inactive or slowly dividing cells located in the root promeristem, positioned between the root cap and the more actively dividing cells of the root apical meristem. Despite its seemingly inactive appearance, the quiescent centre plays a crucial role in root development and meristem function. This region serves as the site of synthesis of plant hormones, particularly auxins, which regulate cell division and differentiation in the meristem. The quiescent centre is also considered the ultimate source of all meristematic cells that comprise the root apical meristem, meaning that the meristematic cells in the surrounding regions are ultimately derived from cells in the quiescent centre. The quiescent centre thus represents a reservoir of meristematic potential that maintains the long-term growth capacity of the root. The concept explains how the root apical meristem can sustain continuous growth throughout the life of the plant while maintaining its structure and organization.

Meristematic tissue and permanent tissue represent two distinct categories of plant tissues that differ fundamentally in their cellular characteristics and functions. Meristematic tissue consists of cells that retain the ability to divide repeatedly through mitosis, maintaining an active growth phase. The cells within meristematic tissue are undifferentiated, meaning they have not yet specialized for specific functions and retain the capacity to develop into various cell types. Meristematic cells are typically small and isodiametric, having roughly equal dimensions in all directions. These cells lack intercellular spaces, as they are tightly packed together, and they contain few or no vacuoles, with the cytoplasm filling most of the cell volume. The cell walls of meristematic cells are thin and flexible, allowing for cell division and growth. Inorganic inclusions are absent in meristematic cells. In contrast, permanent tissue consists of cells that have completed their division and have become fully differentiated, specializing for specific functions such as photosynthesis, support, or transport. Permanent tissue cells do not divide and are adapted for their particular roles. The cells are variable in shape and size, reflecting their specialized functions. Intercellular spaces are present in many permanent tissues, facilitating gas exchange and other physiological processes. Vacuoles are typically present and often large, occupying significant portions of the cell volume. Cell walls may be thick or thin depending on the tissue type and its function. Inorganic inclusions such as crystals, silica, or other mineral deposits are often present in permanent tissue cells.

Dicot leaves and monocot leaves exhibit significant structural differences that reflect their distinct evolutionary adaptations and physiological requirements. The most fundamental difference is that dicot leaves are dorsiventral, meaning they have distinct upper and lower surfaces with different structures and functions. In dicot leaves, the mesophyll, the photosynthetic tissue between the upper and lower epidermis, is clearly differentiated into two layers: the palisade parenchyma and the spongy parenchyma. The palisade parenchyma consists of elongated, columnar cells arranged perpendicular to the leaf surface on the upper side, optimized for capturing light energy. The spongy parenchyma lies beneath the palisade tissue and consists of loosely arranged cells with large intercellular spaces that facilitate gas exchange. In contrast, monocot leaves are isobilateral, meaning they have similar structures on both the upper and lower surfaces. In monocot leaves, palisade parenchyma is present on both the upper and lower surfaces of the leaf, providing photosynthetic capacity from both sides. The spongy parenchyma lies in the centre between these two layers of palisade tissue. This isobilateral structure is an adaptation to the growth habit and environmental conditions typical of monocots such as grasses, where leaves are often held vertically or at steep angles, allowing both surfaces to receive significant light exposure. Sunflower is a typical example of a dicot with a dorsiventral leaf, while grass is a typical monocot with an isobilateral leaf.

Stomata are minute pores surrounded by two guard cells and occur mainly in the epidermis of leaves. In some plants, in addition to guard cells, specialised epidermal cells are present which are distinct from other epidermal cells. These are called subsidiary cells. Subsidiary cells are morphologically and functionally different from the ordinary epidermal cells and are closely associated with the guard cells. Based on the number and arrangement of subsidiary cells around the guard cells, various types of stomata are recognized, such as anomocytic, anisocytic, paracytic, and diacytic types. The guard cells and subsidiary cells work together to regulate the opening and closing of stomata during gaseous exchange and transpiration. The subsidiary cells help in the movement of guard cells by providing mechanical support and assisting in the osmotic changes that cause the guard cells to open and close. This coordinated action between guard cells and subsidiary cells ensures efficient control of water loss and gas exchange in plants.

Bulliform or motor cells and silica cells are both specialized epidermal cells found in grasses, but they have distinct structures and functions. Bulliform or motor cells are large, thin-walled cells located in the upper epidermis of grass leaves. These cells are helpful for the rolling and unrolling of the leaf according to weather changes in order to check transpiration. When the plant experiences water stress, these cells lose water and collapse, causing the leaf to roll up, which reduces the exposed surface area and minimizes water loss. When water becomes available again, these cells regain turgor and the leaf unrolls. Silica cells, on the other hand, are some of the epidermal cells of grass that are filled with silica, a hard mineral compound. They provide mechanical stability and protection to the tissues by strengthening the cell walls and making them more rigid. Silica cells also help protect the plant from herbivory and mechanical damage. While bulliform cells are involved in dynamic leaf movement and water conservation, silica cells provide static structural support and protection.

The outermost layer of the root is known as the piliferous layer or epiblema. It consists of a single row of thin-walled parenchymatous cells without any intercellular spaces. The piliferous layer is distinct from the typical epidermis of the shoot because epidermal pores and cuticle are absent in this layer, allowing for direct contact with soil particles and water. Root hairs that are found in the piliferous layer are always unicellular extensions of the epidermal cells. These root hairs greatly increase the surface area available for absorption and are the primary organs for absorbing water and mineral salts from the soil. Root hairs are generally short-lived, lasting only a few weeks before being shed and replaced by new ones as the root grows. The main function of the piliferous layer is protection of the inner tissues of the root from mechanical damage and desiccation. Additionally, the piliferous layer plays a crucial role in the selective absorption of water and minerals, as the cells are living and metabolically active, allowing them to regulate what substances enter the root.

Sieve tubes and vessels are both important conducting elements of vascular tissue but differ in their location, composition, and function. Sieve tubes are components of the phloem and are formed by the fusion of cells to create a syncyte, which is a multinucleate structure. Although sieve tubes are syncytes, they are living cells that contain a lining layer of cytoplasm, making them known as living syncytes. The nucleus is absent in mature sieve tubes, but the presence of cytoplasm allows them to conduct organic food materials. Sieve tubes are associated with companion cells that help regulate their function. Vessels, on the other hand, are components of the xylem and are also syncytes formed by the fusion of cells. However, vessels are dead cells at maturity, with no nucleus or cytoplasm, making them non-living syncytes. The cell walls of vessels are heavily lignified, providing mechanical support. Vessels conduct water and mineral salts from the roots to other parts of the plant. While sieve tubes conduct organic foods from leaves to other parts, vessels conduct water and minerals. Sieve tubes have sieve plates at their ends that allow movement between cells, whereas vessels have perforations that allow water to move freely through the vessel elements.

Amphicribral and Amphivasal vascular bundles are both types of concentric vascular bundles in which xylem and phloem are arranged in concentric circles, one around the other. In some stems, these two types of concentric arrangements are found. In amphicribral or halocentric vascular bundles, the xylem lies in the centre and the phloem surrounds it on all sides. This arrangement is found in ferns such as Polypodium and in some aquatic dicots. The central xylem is completely enclosed by the phloem tissue, providing protection to the water-conducting elements. In amphivasal or leptocentric vascular bundles, the arrangement is reversed, with the phloem lying in the centre and the xylem surrounding it on all sides. This type is found in plants such as the dragon plant Dracaena and Yucca. The central phloem is completely enclosed by the xylem tissue. Both types of concentric bundles are less common than collateral bundles and are typically found in plants with unusual growth patterns or in specialized tissues. The concentric arrangement in both cases provides structural support while protecting the delicate conducting tissues from external damage.

The vascular bundles of dicot and monocot roots show several important anatomical differences that reflect their different growth patterns and functions. In dicot roots, the vascular tissue consists of a usually limited number of xylem and phloem strips arranged in a radial pattern. The conjunctive tissue between the vascular bundles is parenchymatous, and its cells are differentiated into vascular cambium, which is a secondary meristem that appears at the time of secondary growth. This vascular cambium allows dicot roots to undergo secondary growth, increasing their diameter over time. The xylem in dicot roots is usually tetrarch, meaning there are four xylem poles. In monocot roots, the vascular tissue consists of a usually greater number of xylem and phloem strips, also arranged radially. The conjunctive tissue is mostly sclerenchymatous, though sometimes it can be parenchymatous, and it is never differentiated into vascular cambium. Because there is no vascular cambium, monocot roots do not undergo secondary growth and remain relatively constant in diameter. The xylem in monocot roots is usually polyarch, meaning there are many xylem poles, often more than four. These differences reflect the fact that dicot roots are capable of increasing in thickness through secondary growth, while monocot roots maintain a relatively fixed structure throughout their life.

Kranz anatomy is a specialized leaf anatomy characteristic of C4 plants, such as maize, sugarcane, and sorghum, which enables them to efficiently fix carbon dioxide at low concentrations and high temperatures. The term 'Kranz' is German for 'wreath' or 'halo,' referring to the distinctive arrangement of cells around the vascular bundles. In plants exhibiting Kranz anatomy, the vascular bundles are surrounded by two concentric rings of cells. The inner ring consists of large, thick-walled bundle sheath cells that are rich in chloroplasts and often contain starch grains. These bundle sheath cells are typically large and have few, if any, intercellular spaces. The outer ring is composed of mesophyll cells, which are also chloroplast-rich but are arranged more loosely and have smaller chloroplasts compared to the bundle sheath cells. This anatomical uniqueness, where the bundle sheath cells have large chloroplasts while the surrounding spongy mesophyll tissue has fewer or smaller chloroplasts, is crucial for the C4 pathway. The bundle sheath chloroplasts often lack grana (agranal chloroplasts) or have reduced grana, and they are the site of the Calvin cycle, while the mesophyll cells are where the initial CO2 fixation occurs. This spatial separation of photosynthetic processes in Kranz anatomy helps to concentrate CO2 around RuBisCO in the bundle sheath cells, minimizing photorespiration and enhancing the efficiency of CO2 fixation, especially in hot and dry environments, making C4 plants more productive than C3 plants under such conditions.

The phloem in the dicot stem shows a characteristic arrangement and composition. The primary phloem lies towards the periphery of the stem, just internal to the cortex. It consists of protophloem and metaphloem, which are the earlier and later formed portions of the primary phloem respectively. The protophloem is crushed and obliterated as the stem grows, while the metaphloem remains functional. The phloem tissue consists of sieve tubes, which are the main conducting elements for organic food transport, companion cells, which are associated with sieve tubes and help regulate their function, and phloem parenchyma, which stores food materials. Notably, phloem fibres are absent in the primary phloem of dicot stems, though they may be present in the secondary phloem that forms later during secondary growth. The primary function of the phloem is to conduct organic food materials, particularly sugars and other photosynthetic products, from the leaves to other parts of the plant body such as roots, stems, and developing fruits and seeds. The sieve tubes are living cells with perforated sieve plates that allow the movement of food materials from one cell to the next. The presence of companion cells ensures that the sieve tubes remain functional and viable for the translocation of organic compounds throughout the plant.

1. Vascular bundles: Vascular bundles are scattered (atactostele) in the parenchyma ground tissue. Each vascular bundle is surrounded by a sheath of sclerenchymatous fibres called bundle sheath. The vascular bundles are conjoint, collateral, endarch and closed. Vascular bundles are numerous, small and closely arranged in the peripheral portion. Towards the centre, the bundles are comparatively large in size and loosely arranged. Vascular bundles are skull or oval-shaped.
2. Phloem: The phloem in the monocot stem consists of sieve tubes and companion cells. Phloem parenchyma and phloem fibres are absent. It can be distinguished into an outer crushed protophloem and an inner metaphloem.
3. Xylem: Xylem vessels are arranged in the form of ‘Y’ the two metaxylem vessels at the base. In a mature bundle, the lowest protowylem disintegrates and forms a cavity known as protoxylem lacuna.

• Schuepp (1917)- proposed it
• According to it, Root system has 2 zones – Korper and Kappe
• Korper – zone forms body and Kappe forms the cap
• This theory is comparable to Tunica – corpus theory of shoot apex.

• Sieve tubes are long tubes formed by a series of cells known as sieve tube elements.
• Arranged one above another to form vertical sieve tube.
• No. of pores occur on end walls – known as sieve plate.
• Sieve plates may be simple or compound.
• Sieve elements show nacreous thickening on their lateral walls.
• Mature sieve tube, nucleus is absent, only lining layer of cyto plasm, a special phloem protein (slimy body) is seen in it.
• Mature sieve tubes pores blocked by a substance known as callose (callose plug) sieve tube function as food conducting tissue Angiosperm.

The root and stem are two major organs of the plant body and show significant anatomical differences that reflect their different functions and environments. In terms of epidermis, the root lacks a cuticle and epidermal pores, whereas the stem has a well-developed cuticle and epidermal pores. The root bears unicellular root hairs that are specialized for water and mineral absorption, while the stem bears both unicellular and multicellular trichomes that serve protective and other functions. In the outer cortical cells, the root lacks chlorenchyma because it is underground and does not receive light, whereas the stem has chlorenchyma in the cortex that is capable of photosynthesis. The endodermis is well-defined in the root with a characteristic Casparian strip, but it is ill-defined or absent in the stem. The vascular bundles show different arrangements: in the root they are arranged radially, with xylem and phloem alternating, whereas in the stem they are arranged conjointly, typically in a ring in dicots or scattered in monocots. The xylem maturation also differs: in the root, xylem is exarch, meaning the protoxylem is towards the periphery and metaxylem towards the centre, whereas in the stem, xylem is endarch, with the protoxylem towards the centre and metaxylem towards the periphery. These anatomical differences reflect the specialized functions of each organ: roots absorb water and minerals, while stems provide support and conduct materials.

The tissue systems of plants can be classified into three main types based on their origin, composition, and function. The epidermal tissue system forms the outermost covering of the plant and originates from the protoderm. It consists of epidermal cells, stomata, and epidermal outgrowths such as trichomes and root hairs. Its primary functions are protection of the plant body, absorption of water in roots, gas exchange for photosynthesis and respiration, and transpiration in shoots. The ground or fundamental tissue system forms the ground meristem and comprises simple permanent tissues such as parenchyma and collenchyma. This tissue system gives mechanical support to the organs and is responsible for the preparation and storage of food in leaves and stems. The vascular or conduction tissue system originates from the procambial bundles and consists of xylem and phloem. The xylem conducts water and mineral salts from the roots to other parts of the plant, while the phloem conducts organic food materials from the leaves to other parts. Both xylem and phloem also provide mechanical strength to the plant organs. Together, these three tissue systems work in coordination to ensure the proper functioning, growth, and survival of the plant body.

Dicot stems and monocot stems show several important anatomical differences that reflect their different growth patterns and structural organization. The hypodermis, which is the layer just beneath the epidermis, is collenchymatous in dicot stems, providing flexible mechanical support, whereas in monocot stems it is sclerenchymatous, providing rigid mechanical support. The ground tissue in dicot stems is differentiated into distinct regions: cortex, endodermis, pericycle, and pith, each with specific functions, whereas in monocot stems the ground tissue is not differentiated but forms a continuous mass of parenchyma. The starch sheath, also called the starch-containing endodermis, is present in dicot stems but absent in monocot stems. Medullary rays, which are radial bands of parenchyma that extend from the pith to the cortex, are present in dicot stems but absent in monocot stems. The vascular bundles differ significantly: in dicot stems they are collateral and open, meaning they have the potential for secondary growth due to the presence of vascular cambium, and they are arranged in a ring or cylinder around the pith. In monocot stems, the vascular bundles are collateral and closed, lacking vascular cambium, and they are scattered throughout the ground tissue rather than arranged in a ring. Finally, secondary growth occurs in dicot stems due to the activity of vascular cambium and cork cambium, whereas secondary growth usually does not occur in monocot stems because they lack vascular cambium. These differences result in dicots having woody stems that increase in diameter, while monocots typically have herbaceous stems that remain relatively constant in diameter.

The transverse section shows the following structure.
Piliferous layer or Epiblemma or Rhizodermis;
* Single-layer of parenchyma cells compactly arranged with out inter cellular space, devoid of circle and stomata (epidermal pores)
* Single called root hairs arise from the small cell known as trichoblast
Function: Protection & absorption
Cortex:
* Made of loosely arranged parenchyma cells with intercellular spaces.
* Starch grains are stored in, them leucoplasts occur in the cells.
Endodermis:
* Inner most layer of cortex – made up of single layer of barrel-shaped parenchyma cells.
* The radial and inner tangential walls have suberin and lignin thickening known as Casparian thickening.
* The cells opposite to protoxylem do not have Casparian thickening, known as Passage cells, which allow water to pass through but not the cells with Casparian thickening.
Stele:
All the tissue present inside endodermis comprise the stele, include pericycle & vascular bundle,
a) Pericycle:
Outer most layer of stele Single layer of parenchyma. The lateral roots originate from pericycle, so known to have endogenous origin.
Vascular bundle:
Made up of xylem and phloem.
Radial arrangement: In dicot root xylem and phloem are in different radii known as radial arrangement.
Exarch condition:
The protoxylem is pointing towards the periphery.
Tetrarch:
There are four protoxylem points, present this condition is known as tetrarch. Conjunctive tissue: The parenchyma tissue that separates xylem and phloem are known tissue.
Metaxylem – Vessels: are generally polygonal in cross-section.
Pith or Medulla: absent.

• Vascular bundles are skull-shaped, numerous, bigger bundles towards the centre and numerous small bundles arranged in the periphery.
• Vascular bundles are scattered in the parenchymatous ground tissue. This condition is known as Atactostele.
• V – Bs Conjoint Collateral, Closed and Endarch in nature
• Pith or Medulla is absent.

Epidermis:
A single layer of compactly arranged rectangular parenchymatous cells, with out intercellular space. Cuticle: on the outer walls check transpiration
Stomata: may be present here and their Chloroplasts: usually absent Multicellular hairs: occur in large numbers Function: Protective Cortex:
Lies below epidermis has 3 zones
1. Hypodermis:
Epidemial hay Made upof few layers of colknchyma cells liv- Cuticleing with thickenings at the successive tangential Epidenms avers giving mechanical inheiweeit
2. Chloresrchma:
A few layers below hypodermis with resin ducts in between
3. Parenchyma:
3rd zone, store food material.
Lndodermis or Starch Sheath:
inner most layer of cortex. barrel-shaped cells compactly managed without intercellular spaces.
Since starch grains are abundant in it. It is also a Medullary ray known as starch sheath, homologous to endodermis of root.
Stete: fonn a central ring inner to endodermis made up of Pericycle, VascuLar bundle & Pith.
Perlccle: A few layer of sclerenchyma outside the phloem, known as Hundk cap or Hard bast and also parenchynia cells between them constitute pericycic.
Vascular bundles:
Muscular bundles wedge-shaped arranged the form of a ring – (Eustelic)
Vascular bridle is made upon xylem. Phloem and cambium.
V – B is Conjoint, Collateral. Open and Endarch
Phloem: lies towards periphery.
Function: Conduction of organic food material
Cambium: brick-shaped thin-walled meristem responsible for secondary growth so. V – B is known as open V – B.
Function: Conduction of water and mineraLs from root to other parts.
Pith (Medulla): Central pith is present. It is parenchymatous.
Medullar ray: Pith extends between V – Bs as primary medullary ray.
FunctIon: Storage.

A single layer of thin-walled cells with outer walls covered by thick cuticle.
* Stomata occur on both epidermis – stomata surrounded by dumbbell-shaped guard cells.
* Subsidiary cells: Surround guard cells.
* Bulliform cells: Occur on upper epidermis help for the rolling and un rolling of the leaf according to the weather change.
* Silica ceils: Some epidermal cells are filled with silica
Mesophyll:
* Grass, being isobilateral, mesophyll is not differentiated into palisade and spongy tissue, but compactly arranged cells with limited intercellular space.
Vascular Bundles:
* V.Bs differ in size – most of them are smaller, Large bundles occur at regular intervals
* Above and below large bundles sclerenchymatous patches occur – provide mechanical support, they are
* absent in small bundles.
* Bundle sheath – Each V.B is surrounded by a parenchymatous bundle sheath, generally contain starch grains.
* V.B has xylem upward and phloem towards the lower epidermis.
* V.Bs are Conjoint Collateral and Closed.
* In C 4 grasses the bundle sheath cells are called Kranz sheath, involve in C 4 cycle.

• Multiseriate upper and lower Epidermis.
• Thick cuticle on the surface of upper epidermis
• Mesophyll is distinguished in to upper palisade and lower spongy parenchyma.
• Well developed vascular bundles with upper xylem and lower phloem (conjoint collateral closed V.B).
• Sunken stomata on the lower epidermis with trichomes, to reduce the rate of transpiration.

Stomata and hydathodes are both pores found in the leaves of plants, but they differ significantly in their location, structure, and function. Stomata occur in the epidermis of leaves and young stems and are found on most plants. The stomatal aperture is guarded by two guard cells that are specialized for regulating the opening and closing of the pore. The two guard cells are generally surrounded by subsidiary cells that assist in the movement and regulation of the guard cells. The opening and closing of the stomatal aperture is actively regulated by the guard cells in response to light, temperature, water availability, and other environmental factors. Stomata are primarily involved in transpiration and the exchange of gases such as carbon dioxide and oxygen. Hydathodes, on the other hand, occur at the tip or margin of leaves, particularly in plants that are grown in moist, shady places. The aperture of hydathodes is surrounded by a ring of cuticularized cells rather than guard cells, and subsidiary cells are absent. Unlike stomata, the pores of hydathodes remain always open and cannot be closed. Hydathodes are involved in guttation, which is the process of water loss from the leaves in the form of liquid water droplets, rather than as water vapour. This occurs when the root pressure is high and the plant is unable to transpire water vapour due to high humidity or closed stomata. While stomata are dynamic structures that regulate gas exchange and water loss, hydathodes are passive structures that allow excess water to be expelled from the plant.