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Here is a list of thirteen leaf found in plants.
1. Leaf of Mangifera Indica (Family: Anacardiaceae):
A thin transverse section of leaf reveals the following internal tissue organization (Fig. 31.45).
Epidermis:
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It occurs on adaxial and abaxial surface of leaf and accordingly termed as upper and lower epidermis. Both epidermal layers are uniseriate and composed of tabular cells. The cells are compactly set and are covered with cuticle on their outer walls. The upper epidermis is continuous and the cuticle is thick in contrast to lower epidermis. The continuity of lower epidermis is interrupted by stomata.
Mesophyll:
It occurs in between upper and lower epidermis. It is distinguishable into palisade and spongy parenchyma. Palisade tissue lies just internal to upper epidermis and is composed of elongated columnar parenchyma, which is arranged perpendicular to upper epidermis. They are compactly set and contain abundant chloroplastids on their radial walls.
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Palisade parenchyma consists of two layers of cells and occurs as a continuous band. The cells of bundle sheath extension situated above the large vascular bundles may interrupt the continuity. Though palisade cells are compactly set, small intercellular spaces are present and each cell is in contact with the spaces.
These spaces are in continuity with the intercellular spaces formed by the spongy parenchyma. Spongy parenchyma is present towards the lower epidermis. They are many layered and occur as a continuous layer except at the bundle sheath extension region.
The cells are more or less isodiametric, loosely arranged with conspicuous intercellular spaces and enclose small air spaces. They contain lesser number of chloroplast in contrast to upper palisade.
Vascular bundle:
The bundles are collateral, closed with mesarch xylem. Phloem occurs towards the lower epidermis and xylem lies towards the upper epidermis. The bundles are of various sizes. A layer of bundle sheath made up of parenchyma surrounds the smaller bundles.
In the large bundles, in addition to bundle sheath, there occur thin or thick walled parenchyma cells above and below, and they connect the bundle with upper and lower epidermis.
This is bundle sheath extension where the mesophyll tissue is discontinuous. In the xylem element trachea with annular and spiral thickening, and xylem parenchyma are present. In the phloem, sieve tubes with narrow lumen, companion cell and phloem parenchyma occur.
Comment:
Epidermis with cuticle protects the inner mesophyll tissues. Stoma present on the lower epidermis is meant for gaseous diffusion. Mesophyll cells are photosynthetic tissue. It is differentiated into palisade and spongy parenchyma, and it is the characteristic of dicotyledonous dorsiventral leaf.
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Inverted vascular bundle is the characteristic of leaf. Stoma at lower epidermis, differentiated mesophyll cells and inverted vascular bundles are the characteristic of typical dorsiventral mesophytic leaf.
2. Leaf of Ficus sp. (Family: Moraceae):
A vertical section through the leaf shows the following anatomical characters (Fig. 31.46).
Epidermis:
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There are two epidermal layers upper and lower. The upper epidermis is multiseriate and the cells are compactly set. The outermost layer consists of elongated cells with cuticle on the outer walls. This layer is continuous and devoid of stomata. The lower layers of upper multiple epidermis are interrupted by the lithocysts. Lithocyst is a large cell that contains cystolith.
It is composed of a cluster of crystals of calcium carbonate and remains attached to the roof of lithocyst by means of a stalk. The cells of lower layers of upper epidermis are larger than the outermost layer. All cells lie above the upper palisade cells. The lower epidermis is also multiseriate and consists of cells that are compactly arranged.
The cells are more or less of same size. The outermost layer of lower epidermis has cuticle on the outer walls but the degree of cutinization is less than the upper epidermis. The lower epidermis is interrupted by stomata.
The stomata are sunk and below each stoma there exists the sub-stomatal chamber. In some species cystoliths also occur on the lower side. They are smaller in size than those occurring on the upper side. The lithocysts are larger than the adjacent cells and some of its portion may intrude the spongy parenchyma cells.
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Mesophyll:
It lies between upper and lower layers of multiple epidermis. The cells situated towards the upper epidermis are coloumnar, two or more layered and contain abundant chloroplast. These are called palisade cells that compose the chief photosynthetic region of the leaf. The cells that occur towards the lower epidermis are more or less isodiametric and may be irregular in shape.
The cells are loosely arranged and have profuse intercellular spaces. The cells are called spongy parenchyma and contain lesser number of chloroplasts in comparison to palisade parenchyma. The mesophyll cells may be interrupted by bundle sheath extensions.
Vascular bundle:
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The vascular bundle remains embedded in the mesophyll tissue and the size of it varies. The bundles are collateral and closed. The bundles are surrounded by bundle sheath (border parenchyma), which is parenchymatous and colourless.
The large bundles have bundle sheath extension. Each vascular bundle has xylem that occurs towards the upper epidermis and phloem that lies towards the lower epidermis. In large vascular bundles sclerenchyma patches are present above xylem and below phloem. It is absent from smaller bundles.
Comment:
Multiple epidermis with cuticle protects the inner tissues. Mesophyll cells are distinguishable into upper palisade and lower spongy cells. This is the characteristic of dorsiventral leaves. Inverted vascular bundle, i.e. xylem towards the upper side and phloem towards the lower epidermis is the characteristic of leaves.
The vascular bundles beside from normal functions provide mechanical strength against shearing stress. The stoma is present on the lower epidermis only. It is sunken and characteristic of leaves that have xerophytic adaptation.
3. Leaf of Musa Sopientum (Family: Musaceae):
A vertical section of leaf reveals the following internal tissue organization (Fig. 31.47).
Epidermis:
It consists of upper and lower epidermis. The upper epidermis is uniseriate and consists of cells that are thin walled, more or less round and compactly arranged with prominent and well-developed cuticle on outer walls. The lower epidermis is also uniseriate and the cells are like the upper epidermis.
But the cuticle is not prominent and well developed like upper epidermis. The continuity of lower epidermis is interrupted by the presence of stomata. Presence of stoma is restricted to lower epidermis only and it is slightly sunken. Below each stoma a prominent sub-stomatal chamber is present.
Below the upper and lower epidermis there occur one or more layers of cells. This layer is termed as sub-epidermal layer. The cells of this layer are thin walled, parenchymatous and devoid of chlorophyll. These cells have water storage function. The cells of subepidermal layer below upper epidermis are much larger than those present below the lower epidermis.
Mesophyll:
It is differentiated into palisade tissue and spongy parenchyma. The palisade tissues are two to three layered and occur below the upper epidermis. The cells are columnar and compactly arranged with little intercellular spaces. The cells contain chloroplastids on their radial walls. The palisade layer is discontinuous above the vascular bundles where patches of sclerenchyma cells are present. The spongy parenchyma is situated below the palisade zone.
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The cells are smaller than the palisade cells. The shape of the cell is more or less isodiametric. The cells that are present below the lower epidermis are almost round. These cells contain chloroplastids. The zone of spongy parenchyma is interrupted by the presence of large air spaces. The spaces develop lysigenously. These spaces alternate with the vascular bundles. The spongy layer is also discontinuous below the vascular bundle where sclerenchyma is present.
Vascular bundle:
Each vascular bundle is oval in shape. The bundles are collateral and closed. Xylem occurs towards the upper epidermis and is poorly developed. The phloem occurs towards the lower epidermis. Each vascular bundle is surrounded by a bundle sheath made up of parenchyma. Sclerenchymatous patches occur above and below of each vascular bundle.
Comment:
The leaf nature is revealed by the presence of collateral and inverted vascular bundle where xylem occurs towards the upper epidermis and phloem lies towards the lower epidermis. The cambium is absent. The leaf is dorsiventral due to the differentiation of mesophyll into palisade and spongy parenchyma. Large air spaces are meant for gaseous diffusion.
Musa, though monocot, possesses differentiated mesophyll tissues, which are the characteristic of dicotyledonous leaf. Each vascular bundle with sclerenchymatous caps forms I-girder where the patches of sclerenchyma form the flanges and the vascular bundles the web. These I-girders provide mechanical strength against shearing stress.
4. Leaf of Nerium Odorum (Family: Apocynaceae):
A vertical section through the lamina of leaf reveals the following internal organization of tissues (Fig. 31.48).
Epidermis:
There are two epidermal layers that occur towards the upper and lower side. They are accordingly called upper epidermis and lower epidermis.
The upper epidermis is multiseriate, usually composed of three layers. The cells are more or less isodiametric, thin walled and compactly arranged. The peripheral layer is covered with thick cuticle on their outer walls. The lower epidermis is also multiseriate and the cells are like upper epidermis. Epidermal outgrowths occur on both adaxial and abaxial epidermal layers.
The continuity of lower epidermis is interrupted by the presence of stoma that is present on lower epidermis only in cavities. The cavities are called stomatal pit. It is formed by the incurvation of epidermis.
The cavities are lined by epidermal cells, which are discontinuous at the region of stomata. The stoma is slightly elevated above the epidermal layer that borders the cavities. Numerous unicellular hairs are present in the cavity and they are the prolongations of cells that border the cavity.
Mesophyll:
It is composed of palisade parenchyma and spongy parenchyma. The palisade cells occur below the upper and lower epidermis. On the upper side the palisade cells are three or more layered. The cells are columnar, compactly arranged with few intercellular spaces. The cells contain abundant chloroplastids that usually occur along the radial walls of the cells.
In contrast to the upper palisade layer the inner palisade is single layered and the cells are smaller. The spongy cells occur in between upper and lower palisade layers. It is many layered. The cells are more or less isodiametric and thin walled. The cells are very loosely arranged in such a way that they enclose large air spaces. In the mesophyll there occurs the calcium oxalate Crystals here and there.
Vascular bundle:
The bundles are collateral and closed, i.e. cambium is absent and xylem and phloem lie radially. The xylem occurs towards the upper epidermis and phloem is towards the lower epidermis. Each bundle is surrounded by bundle sheath. It is composed of parenchyma cells.
Comment:
The leaf is dicot and dorsiventral due to the presence of differentiated mesophyll cells into palisade and spongy parenchyma. Unlike other dicots palisade cells occur below both upper and lower epidermal layers. Xylem is the only mechanical cell.
The leaf shows xerophytic adaptations due to the presence of:
(i) Abaxial and adaxial multiple epidermal layers,
(ii) Thick cuticularization on the outer wall of cells composing both the epidermal layers,
(iii) Occurrence of multilayered palisade cells,
(iv) Occurrence of stoma in stomatal pit and
(v) Presence of hairs in the pit to reduce the rate of transpiration.
5. Leaf of Polianthes Tuberose (Tube rose; Family: Agavaceae):
A vertical section through the leaf reveals the following anatomical features (Fig. 31.49).
Epidermis:
It occurs on adaxial and abaxial surfaces of a leaf and accordingly termed as upper epidermis and lower epidermis. The epidermal layers are single layered. The cells are rectangular in shape with rounded outer walls. The outer walls are cuticularized. The cells are compactly set. The continuity of both epidermal layers is interrupted by stomata. A sub-stomatal chamber is present below each stoma. Stomata are flush with the epidermis.
Mesophyll:
It lies in between the two epidermal layers and is many layered. It consists of similar type of cells. The cells are more or less isodiametric. The cells contain abundant chloroplastids. The cells cannot be differentiated into palisade parenchyma and spongy parenchyma, but the cells are of spongy type. The cells enclose intercellular spaces that are continuous to the external environment through sub-stomatal chamber and stomata.
Vascular bundle:
The bundles are more or less of same size and shape. They are situated at regular intervals. Each vascular bundle is collateral and closed, i.e. cambium is absent. The xylem occurs towards the upper epidermis and the phloem lies towards the lower epidermis. Above xylem and below phloem there occurs a patch of sclerenchyma. Each vascular bundle is surrounded by a bundle sheath. It is composed of parenchyma cells. The cells are thin walled and chloroplastids are absent from these cells.
Comment:
It is an isobilateral leaf due to the presence of stomata on both upper epidermis and lower epidermis, and the mesophyll cells are not differentiated into palisade parenchyma and spongy parenchyma.
The mesophyll cells with chloroplastids are photosynthetic tissue. Stomata are meant for gaseous diffusion. Sclerenchyma patches, present above xylem and below phloem, are mechanical cells. They form I-girders and add mechanical strength against shearing stress.
6. Leaf of Zea Mays (Family: Poaceae):
A vertical section through the lamina of leaf reveals the following internal organization of tissues (Fig. 31.50).
Epidermis:
Epidermis occurs on upper and lower surface of leaf. The upper epidermis is uniseriate. The cells are more or less oval with cuticularized outer walls. It is discontinuous where stoma is present. Below each stoma sub-stomatal chamber is present. Upper epidermis possesses the characteristic bulliform cells.
These cells occur in groups and can be easily differentiated from the adjoining cells by their larger size. The cells are hyaline and empty. The lower epidermis is just like the upper epidermis but it is devoid of bulliform cells. It is also interrupted by stoma.
Mesophyll:
It is composed of similar type of cells. It is not differentiated into palisade and spongy parenchyma. The cells are more or less isodiametric and enclose small intercellular spaces. The intercellular spaces are connected with each other and form a continuous system. Mesophyll cells are connected to the external environment through the spaces, sub-stomatal chamber and stoma. Chloroplastids are present in the cells.
Vascular bundle:
The bundles may be large and small. They are arranged in parallel and alternate to each other. Each bundle is collateral and closed, i.e. cambium is absent. Xylem occurs towards the upper epidermis and phloem is situated towards the lower epidermis. The large bundles show distinct xylem and phloem.
There are two metaxylem and one protoxylem vessel. Metaxylem is more or less oval in shape. The lysigenous protoxylem cavity is towards the upper epidermis. Each vascular bundle remains surrounded by a bundle sheath. The sheath is parenchymatous, the cells of which contain starch and plastids.
The cells are thin walled. In large vascular bundle the bundle sheath is connected with upper epidermis and lower epidermis by patches of sclerenchyma. The cells may be of several layered, compactly arranged and appear as a cap over and below the vascular bundle. These cells are called bundle sheath extension.
Comment:
The leaf is monocot because the mesophyll is composed of similar type of cells. Presence of stoma on both epidermal layers and the undifferentiated mesophyll are the characteristic of isobilateral leaf. The numerous vascular bundles remain in parallel. Presence of bulliform cell in the upper epidermis is also the characteristic of a monocot leaf.
The stoma is meant for gaseous diffusion. Presence of starch in the bundle sheath signifies that it is a storage tissue. The large vascular bundles with their sclerenchymatous bundle sheath extensions form I-girder. It gives mechanical strength against shearing stress.
7. Leaf of Bambusa sp. (Family: Poaceae):
A transverse section through leaf shows the following anatomical characters (Fig. 31.51).
Epidermis:
It occurs on adaxial and abaxial surfaces of leaf and accordingly termed as upper epidermis and lower epidermis. The upper epidermis is cuticularized. Bulliform cells occur here and there on the upper epidermis.
The cells are present between the vascular bundles. These cells may not be at the usual level of other epidermal cells. Silica containing cells are also present. The lower epidermis is also cuticularized and possesses stiff sharply pointed hairs. It is not continuous and is interrupted by stoma.
Mesophyll:
It is composed of more or less elongated cells without having any distinction into spongy and palisade tissue. The cells are parenchymatous, compactly arranged and contains chloroplasts. A central row of cavities is present in the mesophyll.
Vascular bundle:
The size of bundle varies. Bundles are arranged in parallel. They are closed and collateral. The bundles are inverted, i.e. xylem occurs on adaxial side and phloem is situated on the abaxial side. Each bundle is surrounded by bundle sheath. The larger bundles have patches of sclerenchyma on adaxial and abaxial side. The sclerenchyma patches may be in contact with upper and lower epidermis.
Comment:
The epidermis with cuticle protects the mesophyll tissues. Bulliform cells help in water storage. The mesophyll cells are not distinguishable into palisade and spongy tissue. This is the characteristic of an isobilateral leaf.
The inverted vascular bundle is the characteristic of leaves. The bundles are arranged in parallel and it is the characteristic of monocot leaf. The bundles provide mechanical strength against shearing stress. Presence of air chamber in the mesophyll helps in gaseous diffusion.
8. Leaf of Phoenix Sylvestris (Datepalm; Family: Palmae):
Cross section of leaf reveals the following internal organization of tissues (Fig. 31.52).
Epidermis:
It occurs on adaxial and abaxial surface and accordingly termed as upper and lower epidermis. Both epidermal layers are uniseriate and composed of tabular cells. The cells are thin walled, compactly arranged and covered with thick cuticle on their outer walls. The continuity of both epidermises is interrupted by the presence of stomata. A uniseriate, thin walled parenchyma with scanty chlorophyll occurs as sub-epidermal layer just internal to both the epidermises.
These sub-epidermal layers are referred to as upper and lower sub-epidermal layer according to their position. They are distinct from mesophyll cells and can be regarded as special hypodermis.
Mesophyll:
It occurs between the two sub-epidermal layers and is not differentiated into palisade and spongy tissue. The cells are polygonal and more or less isodiametric, and enclose small intercellular spaces. Chloroplastids are present in these cells and so they are sometimes referred to as chlorenchyma. Sclerenchyma cells are present in groups internal to both sub-epidermal layers. They occur more or less in parallel series.
Vascular bundle:
Vascular bundles are located in the mesophyll tissue and arranged in parallel. They are variable in size. Each bundle is collateral with xylem present towards upper epidermis and phloem being situated towards lower epidermis. The bundles are closed, i.e. cambium is absent. A uniseriate thin walled hyaline parenchyma cell surrounds the smaller bundles.
This band of parenchyma is known as bundle sheath and it is distinct from mesophyll cells. The larger bundles are also encircled by bundle sheaths, which are made up of sclerenchyma and they may be continuous with the sclerenchyma patches present internal to both epidermises.
Comment:
Epidermis with cuticle protects the inner mesophyll tissues. Stoma is meant for gaseous diffusion. Presence of stoma at both epidermal layers is the characteristic of isobilateral leaf. Undifferentiated homogeneous mesophyll is also the characteristic of an isobilateral leaf. The patches of sclerenchyma situated at the periphery of mesophyll form I-girders and provide mechanical strength against shearing stress. Inverted vascular bundle is the characteristic of a leaf.
The parallel arrangement of bundles reveals its monocotyledonous nature. Sclerenchymatous bundle sheath and sclerenchyma at the two edges of large vascular bundles are mechanical cells.
The leaf exhibits the characteristic of monocot isobilateral xeric leaf due to the presence of stoma on both epidermal surfaces, parallel arrangement of inverted vascular bundles with sclerenchymatous bundle sheath, presence of patches of sclerenchyma at the periphery of mesophyll and homogeneous undifferentiated mesophyll.
9. Leaf of Nymphaea Stellata (Family: Nymphaeaceae):
A vertical section through lamina of leaf reveals the following internal tissue organization:
Epidermis:
It consists of upper and lower epidermis. Both epidermal layers are uniseriate. The cells are more or less round and compactly set. The cells of upper epidermis are cuticularized on their outer walls. Waxy depositions are present over the cuticle. The continuity of upper epidermis is interrupted by the presence of stoma. Below each stoma sub-stomatal chamber is present. The lower epidermis is devoid of stoma and contains slime glands.
Mesophyll:
It consists of upper palisade and lower spongy cells. The palisade cells are three or more layered. The cells are columnar, enclose intercellular spaces and contain chloroplastids. Below palisade layer there lies the spongy parenchyma.
It is many layered and many large air spaces occur in this region. The cells of spongy parenchyma are more or less isodiametric. Some of the cells may form the partition wall between the air spaces. Trichosclereids are present here and there especially on the partition walls of the air spaces.
Vascular bundle:
Each vascular bundle is collateral and closed. They are not well developed. The bundles remain surrounded by a layer of bundle sheath made up of parenchyma.
Comment:
It is a dorsiventral dicot leaf because the mesophyll is differentiated into palisade and spongy parenchyma. Presence of large air space reveals its hydrophytic nature. Presence of stoma on upper surface only signifies that it is a floating leaf. Due to its aquatic habit the vascular and mechanical tissues are reduced.
10. Leaf of Salsola sp. (Chenopodiaceae):
A vertical section through leaf reveals the following internal tissue organization (Fig. 31.53).
Epidermis:
It is single layered and composed of horizontally flattened thin walled cells. The cells are compactly arranged and have thin cuticle on their outer walls.
Mesophyll:
It is differentiated into palisade and parenchyma cell. Palisade cells are elongated and contain abundant chloroplastids. The palisade layer is uniseriate and the cells are compactly arranged. It forms a band of chlorophyllous tissue all round the periphery next to epidermis.
The chlorophyllous band is interrupted at more than one places by parenchyma cells. Below the palisade layer there occur the parenchyma cells. The cells are large, thin walled, centrally located and enclose conspicuous intercellular spaces.
Vascular bundle:
Next to palisade layer there occur the vascular bundles. The vascular tissues are poorly developed. The mechanical cells are scanty. At the centre a large vascular bundle is present. In it xylem and phloem can be distinguished. Phloem occurs towards the lower side.
Comment:
Salsola is halophyte and the leaf is succulent with xerophytic adaptation. The peripheral band of palisade is photosynthetic tissue. The central parenchyma cells store water. Vascular tissues are reduced with scanty mechanical cells. The vascular bundles are inverted, i.e. phloem is towards the lower side and it is the characteristic of a leaf.
11. Leaf of Allium Cepa (Family: Alliaceae):
Transverse section through the leaf appears more of less circular in outline and reveals the following internal tissue organization from periphery towards the centre (Fig. 31.54).
Epidermis:
It is continuous all round the circular peripheral layer. It is uniseriate and composed of parenchyma cells. The cells are more or less round, compactly arranged with well-developed cuticle on outer wall. The continuity of epidermis is interrupted by the presence of stoma that is present all round the epidermal surface. The stoma is slightly sunken.
Mesophyll:
It is composed of palisade tissue and spongy parenchyma. The palisade cells occur towards the peripheral side. It is two layered and the cells are columnar. Abundant chloroplastids are present in them. Below the epidermis palisade layers form a continuous chlorophyllous band all round the surface. The spongy parenchyma occurs below palisade layers.
The cells of spongy parenchyma are more or less oval and contain scanty chloroplastids. The cells are few layered. The mesophyll cells enclose conspicuous air spaces. Below the spongy layer parenchyma occurs. A cavity is present at the centre of leaf. The parenchyma cells that border central cavity are almost barrel-shaped and devoid of chloroplastids.
Vascular bundle:
There are numerous vascular bundles that occur below palisade but among spongy parenchyma. The bundles are scattered in arrangement. Each bundle is collateral and closed. Xylem occurs towards centre and phloem is directed towards the periphery. Each bundle is surrounded by bundle sheath. It is single layered and parenchymatous.
Comment:
The leaf is centric because epidermis is continuous all round the surface and is not differentiated into epidermal layers. Stoma is distributed all round the epidermal surface and meant for gaseous diffusion. Though monocot the mesophyll is differentiated into palisade and spongy cells like dicots.
The arrangement of xylem and phloem is like a stem, i.e. the phloem is directed towards the periphery. The vascular bundles are scattered and this arrangement reveals its monocot nature. Xylem is the only mechanical cell and forms the flanges of an I-girder. It gives mechanical strength against inflexibility.
12. Leaf of Vallisneria sp. (Family: Hydrocharitaceae):
A vertical section through leaf shows the following internal tissue organization (Fig. 31.55).
Epidermis:
It consists of lower and upper epidermis. They are composed of horizontally flattened cells that are compactly arranged with thin cuticle on their outer walls. The stomata are absent from the epidermal layers.
Mesophyll:
The mesophyll is not differentiated. It is composed of parenchyma cells. The cells are more or less isodiametric and of various sizes. They are arranged in such a way that they enclose large air spaces. Undifferentiated mesophyll with air spaces is called lacunate mesophyll.
Vascular bundle:
The bundles may be large and small. The vascular tissues are not clearly differentiated into xylem and phloem.
Comment:
Vallisneria is hydrophyte. The leaf shows hydrophytic characters due to the presence of lacunate mesophyll, reduced vascular tissue and absence of stoma. The air spaces are meant for aeration. They add buoyancy to the plant.
13. Leaf of Portulaca sp. (Family: Portulacaceae):
Vertical section of leaf is more or less oval in outline and shows the following internal tissue organization from periphery towards the centre (Fig. 31.56).
Epidermis:
It is uniseriate and composed of compactly arranged horizontally flattened cells with cuticle on outer walls. It is continuous all round the oval peripheral layer.
Mesophyll:
Below epidermis there lie many circular chlorophyllous zones. In between the zones parenchyma cells are present. They are compactly set, colourless and filled up with mucilage. Parenchyma is also present below the chlorophyllous zones and extends up to the central vascular bundle.
The chlorophyllous zones consist of 2-3 central sclerenchyma cells encircled by two layers of large palisade cells. The peripheral or outer layer of mesophyll is elongated and contains numerous scattered chloroplasts. The inner layer of mesophyll is funnel shaped and also contains chloroplastids. But in this case the chloroplastids are aggregated at the base of the cells.
Vascular bundle:
A central vascular bundle is present. It remains encircled by a layer of border parenchyma. It is colourless. The bundle consists of xylem and phloem.
Comment:
The leaf shows succulent xerophytic adaptation due to the presence of cuticle on epidermis and parenchyma filled with mucilage. The circular chlorophyllous zone is the photosynthetic tissue. Xylem is the only mechanical cell.
