Plant Anatomy - 2013

Section 4. CONTENT MODULE 3. ANATOMICAL STRUCTURE OF VEGETATIVE ORGANS

4.1. Primary and Water/124.html">Secondary Anatomical Structure of the ROOT.

Objects of Study: roots of Iris, roots of buttercup or valerian, roots of pumpkin (Cucurbita pepo), roots of marsh mallow (Althaea officinalis).

Supplies and equipment: microscopes, Glass slides and cover slips, razors, needles, forceps, Petri dishes, chloral hydrate solution, dropper bottles, distilled water, filter paper, wall charts: "Root of a Monocot Plant"; "Root of Introduction/19.html">Primary Structure of a Dicot Plant"; "Pumpkin Root" (fascicular structure); "Root of Non-Fascicular Structure" (fragment); "Tertiary Structure of the Root" (beet).

Task 1.

Prepare a temporary mount of a transverse section of a monocot root and study its microstructure.

Using a razor, make several thin transverse sections of an iris root and mount them in chloral hydrate solution. Clear the sections and examine them under low magnification of the Microscope. Identify the root zones: the protective layer – epiblema (rhizodermis), the primary cortex, and the central vascular cylinder (stele). Under high magnification, examine the microstructure of each zone. Pay attention to the three constituent PARTS OF THE primary cortex: the exodermis, which consists of polygonal, thick-walled Cells tightly fitted together; the mesodermis (inner cortex), which is the broadest part of the cortex with oval, loosely arranged cells and numerous intercellular air spaces; and the endodermis, the innermost layer of the primary cortex consisting of cells with horseshoe-shaped wall thickenings. Thin-walled, unthickened cells can be found interspersed among the thick-walled cells. Note that these are located opposite the xylem radii of the vascular bundle; these are passage cells that perform a conducting function. When examining the central cylinder, point out that it consists of the pericycle, which comprises a single layer of small, thin-walled cells, and a polyarch radial vascular bundle. Right in the center of the root lies the xylem, which in this case is represented by wood parenchyma.

Make drawings of: a diagram of the Anatomical structure of a monocot root (under low magnification), a fragment of the epiblema with the exodermis, and a fragment of the endodermis with thick-walled and passage cells (under high magnification). Label all component parts – root zones, tissue types within the zones, cells with horseshoe-thickened walls, and passage cells. Add figure captions. Write down the Conclusions based on the work performed.

Task 2.

Prepare a transverse section of a dicot root in the absorption zone and study its structure.

In the root Hair zone of a buttercup or valerian root, make several transverse sections and mount them in chloral hydrate solution. After clearing, examine the preparation under low magnification and locate the zones: epiblema, primary cortex, and central cylinder. In the primary cortex, examine the endodermis under high magnification.

Pay attention to the fact that the cells have radial wall thickenings known as Casparian strips. In the central cylinder, examine the radial vascular bundle and count the number of xylem radii (there are no more than five). Draw a low-magnification diagram of the Primary anatomical structure of a dicot root in the absorption zone and label all zones. Under high magnification, draw a fragment of the endodermis with Casparian strips. Add figure captions. Write a Conclusion summarizing the work done.

Task 3.

Prepare a transverse section of an annual dicot root and study its secondary fascicular structure.

Cut a transverse section of a common pumpkin root and mount it in chloral hydrate solution. After clearing, examine the preparation under low magnification. Note the absence of the primary cortex with the endodermis (it has sloughed off), The small size of the secondary cortex, and the secondary protective tissue – the periderm. In the central cylinder, open collateral vascular bundles are arranged in a circle. They are separated by wide radial medullary rays extending from the radii of the primary xylem, which remains from the original radial bundle and is located in the center of the root.

Draw a low-magnification diagram of the secondary fascicular anatomical structure of a dicot root, labeling all zones and Tissues of the root. In the conclusions, describe the results of the work performed.

Task 4.

Prepare a transverse section of a perennial dicot root and study its secondary non-fascicular structure.

Make a transverse section of a marsh mallow root and mount it in chloral hydrate solution. After clearing, examine the preparation under low magnification. Observe the continuous cambium ring, a continuous phloem zone above the cambium, and a continuous xylem zone below the cambium extending all the way to the center of the root. The primary xylem is visible in the center of the root, with primary medullary rays radiating from it. Secondary medullary rays, formed by the cambium, do not reach the primary xylem. Examine all tissues under high magnification, starting from the protective periderm down to the center, and study their components. Note the presence of a small amount of bast (phloem) and wood fibers, which were absent in the previous microscope slides.

Draw a low-magnification diagram of the secondary non-fascicular structure of a dicot root. Under high magnification, draw a fragment of the non-fascicular anatomical STRUCTURE OF THE root in the cambium region, showing areas of phloem and xylem penetrated by medullary rays. Label the zones on the diagram, and the histological elements of the phloem, xylem, and cambium cells on the fragment. Add figure captions. Describe the research results in your conclusions.

4.2. Anatomical structure of the stem and rhizome of monocotyledonous plants

Objects of study: microscopes, glass slides and cover slips, razors, needles, forceps, Petri dishes, chloral hydrate solution, dropper bottles, distilled water, filter paper, wall charts: "Corn Stem"; "Rye Straw"; "Lily of the Valley Rhizome".

Supplies and equipment: corn stem, rye straw, and lily of the valley rhizome.

Task 1.

Prepare a temporary mount of a transverse section of a monocot stem and examine its internal structure.

Using a razor blade, make a thin cross-section of a corn or rye stem and prepare a slide using a chloral hydrate solution. Clear the section and examine it under low magnification. Pay attention to the diagnostic features: scattered (in corn) and checkerboard-arranged (in rye) closed collateral vascular bundles. Under high magnification, carefully examine all tissue types: the dermal tissue (epidermis), the mechanical tissue (sclerenchyma located immediately beneath the epidermis), and the ground parenchyma. Note the absence of a distinct division between the cortex and the central vascular cylinder, as well as the absence of collenchyma. Trace the gradual increase in Cell size of the ground parenchyma toward the center of the stem.

Draw a diagram of the anatomical structure of the monocot stem (corn and rye) based on the low-magnification view of the cross-section. Label all tissues and vascular bundles. Add a title and caption to the drawing. Describe your findings in the conclusions.

Task 2.

Prepare a temporary mount of a transverse section of a monocot rhizome and study its anatomical structure.

Using a razor blade, make several thin cross-sections of a lily-of-the-valley rhizome and mount them in a chloral hydrate solution. Clear the specimen and examine it under low magnification. Identify the anatomical Zones of the organ: the dermal tissue, the cortex, and the central vascular cylinder. Under high magnification, carefully examine all tissues within these zones. The dermal tissue is the epidermis. When examining the cortex, note the oval, loosely arranged Cells of the ground parenchyma, the horseshoe-shaped thickened endodermal cells, and the diagnostic feature of the lily-of-the-valley: a double endodermis. In the central vascular cylinder, locate the pericycle and pericyclic fibers. Pay special attention to Two Types of vascular bundles: closed collateral bundles adjacent to the pericycle, and concentric amphivasal bundles scattered randomly throughout the ground parenchyma of the central cylinder. Recall that amphivasal vascular bundles occur exclusively in monocot rhizomes. Note that the very center of the rhizome consists of ground parenchyma. Raphides are clearly visible within the parenchymal cells of both the cortex and the central cylinder.

Draw a diagram of the anatomical structure of the monocot rhizome (lily-of-the-valley) based on low-magnification observations of the cross-section, and draw a detailed cellular fragment of the rhizome anatomy based on high-magnification observations. Label the zones

and vascular bundles on the diagram, and the zonal tissues, bundles, and raphides on the fragment. Add captions to the drawings. Describe your results in the conclusions.

4.3. Anatomical structure of the stem and rhizome in dicotyledonous plants Subjects of Study: clover stem, yarrow stem, motherwort stem, elderberry branch, bergenia or cinquefoil rhizome, mint or raspberry rhizome.

Materials and equipment: microscopes, glass slides and coverslips, razor blades, dissecting needles, forceps, Petri dishes, dropping bottles, distilled water, chloral hydrate solution, filter paper, botanical charts: "Stem with bundle structure" (birthwort); "Stem without bundle structure" (linden branch, pine branch); "Rhizome with bundle structure" (diagram); "Rhizome without bundle structure" (mint).

Task 1.

Prepare temporary mounts of a transverse section of a dicot stem with a bundle-type structure and examine its microstructure.

Make several thin cross-sections of a clover or yarrow stem and prepare a slide in a chloral hydrate solution. Clear the specimen and examine it under low magnification. Identify the three anatomical zones of the stem: the dermal tissue, the cortex, and the central vascular cylinder. Under high magnification, study the tissues of each zone: the epidermis with trichomes, followed by angular collenchyma in the ridges, then chlorenchyma and the endodermis. In the central cylinder, locate the open collateral vascular bundles arranged in a ring. The yarrow stem exhibits a transitional type of structure. Pay attention to the Abundance of sclerenchyma—specifically pericyclic and bast fibers—and the ground tissue of the broad medullary rays running between the bundles. In the yarrow stem, note the appearance of interfascicular cambium and The formation of additional bundles. Observe that the center of the stem contains the ground parenchyma (pith), followed by a central cavity.

Using low magnification, draw a diagram of the bundle-type anatomical structure of the dicot stem, indicating the following: epidermis, collenchyma, chlorenchyma, endodermis, sclerenchyma, open collateral bundles,

interfascicular cambium, pith, and central cavity. Add a caption to the drawing. Formulate conclusions based on your observations, making sure to mention the transitional stem structure and its diagnostic features.

Task 2.

Prepare a temporary mount of a transverse section of a dicot stem with a non-bundle (solid) structure and examine its microstructure.

Prepare a transverse section of a motherwort or black elderberry stem in a chloral hydrate solution, clear it, and examine it under low magnification. Identify the three zones: dermal tissue, cortex, and central cylinder. Note the absence of discrete vascular bundles; instead, There is a continuous ring of cambium, flanked by a continuous zone of phloem on the outside and a continuous zone of xylem on the inside. Examine the zonal tissues under high magnification. The dermal tissue is represented by the epidermis with trichomes in motherwort, and by the periderm in elderberry. Angular collenchyma is present in the ridges just beneath the dermal layer. Bast fibers are arranged in groups within the phloem. The xylem encloses the pith, from which narrow medullary rays radiate outward,

traversing the xylem, cambium, and phloem. The very center of the stem features a hollow cavity (in motherwort) or a solid pith (in elderberry).

Draw a low-magnification diagram of the non-bundle anatomical structure of the dicot stem in cross-section, labeling all zones and their respective tissues. Add a caption to the drawing. Describe the results of your investigation.

Task 3.

Prepare a temporary mount of a transverse section of a dicot rhizome with a bundle structure and examine its microstructure.

Prepare a transverse section of an elephant ear bergenia (bergenia crassifolia) or tormentil (potentilla erecta) rhizome in a chloral hydrate solution. Clear the preparation and examine it under low magnification. Locate the three anatomical zones: dermal tissue, cortex, and central cylinder. Since the endodermis is indistinct, the BOUNDARIES OF THE central cylinder are determined by the arrangement of its vascular bundles. Observe the ring-like arrangement of open collateral bundles, the fascicular and interfascicular cambium, and the abundance of druses within the ground parenchymal cells (in bergenia) or cells with dark contents (in cinquefoil). Note that mechanical tissues are virtually absent (though isolated fiber groups may occasionally appear in older rhizomes), and the center is occupied by the pith—the ground parenchyma—from which broad medullary rays extend to separate the vascular bundles. Examine the tissues of each zone under high magnification, proceeding from the periderm toward the center.

Based on low-magnification observations, draw a diagram of the bundle-type anatomical structure of the dicot rhizome in cross-section. Label all zonal tissues and cell inclusions on the diagram. In your conclusions, discuss the bundle-transitional structure of the rhizome (the formation of accessory bundles by the interfascicular cambium) and describe the results of your analysis.

Task 4.

Prepare a temporary slide of a cross-section of a dicotyledonous plant rhizome with anon-bundle structure and study its microstructure.

Prepare a cross-section slide of a mint (or raspberry) rhizome in a chloral hydrate solution and clear it. Examine it under low magnification of the microscope to locate three zones: the protective tissue, primary cortex, and central axial cylinder. Pay attention to the clearly defined endodermis with Casparian strips, the continuous cambium ring, and the continuous zones of phloem (above the cambium) and xylem (below it). Note that the xylem, cambium, and phloem zones are radially traversed by very narrow medullary rays. Mechanical tissues are almost absent. The pith is located in the center of the rhizome. Examine all tissues of these zones under high magnification, carefully studying their cellular structure. Using low magnification, draw a diagram of the non-bundle anatomical structure of the dicotyledonous plant rhizome in cross-section. Label all tissue zones on the diagram.

Using high magnification, draw a fragment of the phloem and xylem in the cambium region. Label the drawings. Draw conclusions regarding the research results. In your conclusions, emphasize that the axial Organs of dicotyledonous plants are characterized by open collateral vascular bundles. Furthermore,

make separate conclusions regarding the differences in the anatomical structure of stems and rhizomes, as well as their common features. A common feature is the presence of the pith in the center of the organ.

Distinguishing features:

1) a wide zone of the primary cortex in rhizomes (whereas it is narrow in stems),

2) the near absence of mechanical tissues in rhizomes (whereas they are abundant in stems).

4.4. Anatomical Structure of Leaves in Monocots, Dicots, and Gymnosperms

Objects of study: monocot leaves - Chlorophytum, Asparagus, Iris; dicot leaves - laurel, lingonberry, eucalyptus; gymnosperm leaf - pine needle.

Material provision: microscopes, glass slides and coverslips, razors, needles, forceps, Petri dishes, dropper bottles, distilled water, chloral hydrate solution, filter paper, elderberry pith, charts: "Monocot Leaf"; "Lingonberry Leaf" (bifacial structure); "Eucalyptus Leaf" (isolateral structure); "Pine Needle Section" (radial structure).

Task 1.

Prepare a temporary slide of a monocot leaf cross-section and study its microstructure.

Prepare a cross-section of an iris, Chlorophytum, or asparagus leaf. You can use elderberry pith for this by placing the leaf into a longitudinal slit in the pith, with the midrib parallel to its length. Make several cross-sections (along with the pith), transfer them onto a glass slide, and select the thinnest ones (separating them from the pith). Prepare a temporary slide in chloral hydrate solution and clear it. Examine it under low magnification, then switch to high magnification. Pay attention to the uniformity of the mesophyll: all its cells are oval and loosely arranged. Crystals are visible in some cells. When examining the vascular bundle, note that the xylem faces the upper side of the leaf, while the phloem faces the lower side (i.e., the reverse of axial organs). The closed collateral bundle contains numerous fibers in both the bast and wood portions. In addition, it is densely surrounded by a row of ground parenchyma cells (so-called bundle sheath cells). Also, pay attention to The structure of the epidermis: the upper epidermis consists of larger cells and features a thicker cuticle than the lower one.

Using low magnification, draw a diagram of the anatomical structure of the monocot leaf, labeling: the upper epidermis, uniform mesophyll, closed collateral bundles and their composition, and the lower epidermis. Using high magnification, draw a structural fragment of the monocot leaf (excluding bundles) and label all its tissues. Label the drawings. Draw conclusions from the conducted research.

Task 2.

Prepare a temporary slide of a bifacial dicot leaf cross-section and study its microstructure.

Fix a sweet bay leaf in elderberry pith (with the leaf midrib running along the length of the pith) and make several thin cross-sections, transferring them onto a glass slide. Discard the pith, and from the

leaf sections, prepare a temporary slide in chloral hydrate solution. Clear it and examine the preparation first under low and then under high magnification. Pay attention to the non-uniformity of the mesophyll parenchyma: beneath the upper epidermis lies the palisade parenchyma, whose cells are elongated, tightly packed, and contain METABOLISM/14.html">Chloroplasts. Below the palisade layer lies the spongy parenchyma, which extends all the way to the lower epidermis. Its cells are oval, loosely arranged, with numerous air spaces between them. Some cells of the spongy parenchyma are yellow and filled with essential oil (secretory cells). Examine the vascular bundle of the midrib (an open collateral bundle). The xylem of the bundle faces the upper side of the leaf, and the phloem faces the lower side. Pay attention to the presence of two types of mechanical tissues: collenchyma beneath the upper and lower epidermis of the midrib, and sclerenchyma in the upper and lower parts of the bundle (i.e., wood and bast fibers).

Under low magnification, draw a diagram, and under high magnification, draw a fragment of the bifacial anatomical structure of the dicot leaf in cross-section. On the diagram, label: the upper epidermis, collenchyma, sclerenchyma, open collateral vascular bundle, palisade parenchyma, spongy parenchyma, and lower epidermis. On the fragment, label: the upper epidermis, palisade parenchyma (presence of chloroplasts), spongy parenchyma, oil-containing secretory cells, and lower epidermis. Label the drawings. Describe the research results in your conclusions.

Task 3.

Prepare a temporary slide of an isolateral dicot leaf cross-section and study its microstructure.

Fix an eucalyptus leaf in elderberry pith (with the midrib along the length of the pith) and make several thin cross-sections. Separate the leaf sections from the pith and prepare a temporary slide in chloral hydrate solution. Clear it and examine under low and high magnification. Note that the palisade parenchyma is present not only beneath the upper epidermis but also near the lower epidermis, while the spongy parenchyma occupies a small middle layer between the two palisade layers. Count the number of cell layers in the upper and lower palisade tissues and verify that there are more layers in the upper one.

Pay attention to the large secretory cavities in the leaf mesophyll filled with essential oil, and the presence of druses in the cells of the spongy parenchyma. Examine the vascular bundle and note that its structure is analogous to the previous preparation—the laurel vascular bundle. The mechanical tissues and their arrangement are also analogous.

Using low magnification, draw a diagram of the isolateral anatomical structure of the dicot leaf in cross-section. On the diagram, label: the upper and lower epidermis, upper and lower palisade parenchyma, spongy parenchyma, open collateral vascular bundle, collenchyma, and sclerenchyma.

Using high magnification, draw a fragment of the isolateral anatomical structure of the globe eucalyptus (Eucalyptus globulus) leaf in cross-section. On the fragment, label: the upper and lower epidermis, upper and lower palisade parenchyma, spongy parenchyma, druses, and essential oil secretory cavities. Label the drawings. Draw conclusions from the conducted research.

Task 4.

Prepare a temporary mount of a gymnosperm leaf cross-section and study its microstructure.

Secure the pine needle inside a piece of elderberry pith (longitudinally) and make several thin cross-sections. Remove the pine needle from the elderberry pith, transfer it to a microscope slide, and prepare a temporary mount using a chloral hydrate solution. Clear the mount and examine it first under low magnification and then under high magnification. Pay attention to the radial structure of the pine needle: the presence of the cortical zone terminating in a distinct endodermis with Casparian strips, and the central vascular cylinder containing the conducting system, which consists of two collateral vascular bundles separated by sclerenchyma in the center of the needle. Examine the epidermal cells and the internal thickenings of their cell walls. A hypodermal layer lies beneath the epidermis, with cells similar to sclerenchyma. Special attention should be paid to the cells of the cortical zone of the needle: they feature infoldings directed toward the interior of the cells. This is the plicate mesophyll (fold parenchyma), characteristic exclusively of conifers. Its function is to increase the photosynthetic surface area of the needle. Resin canals surrounded by bast fibers are located within the mesophyll of the cortex. Note that the parenchyma of the central cylinder lacks infoldings; its cells are oval and thin-walled. Observe that the arrangement of phloem and xylem in the vascular bundles follows the general rule observed in leaves: xylem is oriented adaxially (upper side), and phloem is oriented abaxially (lower side).

Under low magnification, draw a diagram of the anatomical structure of the pine needle in cross-section, labeling: the epidermis, hypodermis, plicate mesophyll of the cortex, endodermis, parenchyma of the central vascular cylinder, the two open collateral vascular bundles, and the sclerenchyma between them.

Under high magnification, draw a detail of the cortical region of the pine needle, labeling: the epidermis, hypodermis, plicate mesophyll, resin canal with bast fibers, and epithelial cells. Label the drawings. Describe your findings in the conclusions.

Structure of a Dicot Root (Secondary Growth)

Cucurbita pepo

Prepare a cross-section of the root, 5–6 mm thick, by treating the section with a solution of phloroglucinol in Hydrochloric acid.

In the center, a tetrarch primary xylem is visible, featuring larger vessels alongside smaller, sometimes inconspicuous, xylem elements radiating along its arms.

Radiating outward from the arms of the primary xylem are radial, or medullary, rays—regions of thin-walled living parenchyma (appearing lighter in the preparation). These are produced by the cambium, which originates from the pericycle. Alternating with the medullary rays are broad zones of secondary xylem characterized by large vessels and small-celled wood parenchyma. At the boundary of the secondary xylem, the cambium is clearly visible—typically a thick layer of small, thin-walled cells arranged in regular radial rows. External to the cambium, opposite each secondary xylem sector, lies the secondary phloem, easily recognized by its large sieve tubes and frequently occurring sieve plates.

The cambium that produces the ray parenchyma is less prominent in pumpkin. Externally, it also gives rise to the ground parenchyma. On the outer surface, the root is covered by a thin layer of periderm.

The tissues located outside the cambium (phloem, ground parenchyma, phellogen, and phelloderm) are often collectively referred to as the secondary cortex.

It can be concluded that a root with Secondary structure consists of the xylem (with its radial rays), the cambium, and the secondary cortex.

Stem of Woody Plants: Stem of Linden

Examine the structure of a 3- to 4-year-old linden twig (Tilia cordata) no thicker than a pencil. Insert the linden twig into elderberry pith and cut several thin cross-sections (perpendicular to the axis of the twig), encompassing all tissues from the periphery to the center (making a semi-circular or wedge-shaped section is sufficient). Treat the section with a phloroglucinol-hydrochloric acid solution (alternatively, a permanent double-stained cross-section of a linden twig can be used: in such preparations, lignified cell walls stain red, while unlignified elements and protoplasm stain blue).

In the preparation, annual growth rings of wood can be seen arranged in concentric circles around a small central area. A dark cambium layer is visible surrounding the wood. Outside the cambium lies a series of triangles or trapezoids (with their bases facing the cambium and apexes toward the periphery)—this is the phloem. The phloem triangles are intersected by layers of sclerenchyma that stain red with phloroglucinol. Parenchyma triangles are also situated between the phloem sectors, with their apexes pointing toward the cambium and bases toward the periphery; from the narrow apex of each parenchymatous "triangle" just outside the cambium, a radial row of cells with dark contents extends into the wood—these are the radial (medullary) rays, which function in the vertical Transport of substances. In the phloem, they widen toward the periphery, whereas in the xylem, they are represented by a single row of cells. The phloem sectors and the medullary ray parenchyma separating them together form the so-called secondary cortex, outside of which the primary cortex begins. The primary cortex comprises ground parenchyma consisting of relatively large cells stretched tangentially, within which calcium oxalate druses are frequently found. External to the ground parenchyma, a fine-celled tissue with dense dark contents is visible—this is a layer of lamellar collenchyma, followed by the periderm.

The cork tissue appears as a continuous, indistinct layer due to the dark brown coloration of The Cell walls and the tight packing of the cork cells.

Pith. The pith parenchyma consists of heterogeneous cells that vary in size and content. Some are larger, devoid of living protoplasts, and possess more or less lignified walls. Surrounding them are smaller, living cells, typically containing dark contents rich in Tannins. Closer to the primary wood are smaller cells of the pith (the perimedullary zone) containing starch reserves.

Wood (Xylem). Elements of the primary xylem are discernible around the pith, laid down by the procambium and arranged without a strict pattern. Longitudinal sections show that these primary elements consist primarily of annular and spiral tracheids.

Further outward lie regular radial rows of secondary xylem elements, whose arrangement indicates they are produced by the cambium. The innermost are larger vessels, followed by gradually decreasing xylem elements where tracheids are replaced by smaller tracheids or libriform fibers. In spring, coinciding with the onset of sap flow, the cambium produces vessels; by mid-summer, cambial activity slows down, then resumes active division, but now produces smaller wood elements—tracheids, wood parenchyma, and a small amount of libriform fibers. As new wood cells are added, the cambium layer is pushed outward, displacing all tissues lying exterior to the cambial zone. By autumn, cambial activity declines, only to restart with the spring reactivation, initiating The production of large tracheas once again. Thus, large-diameter vessels immediately follow the small-celled autumn wood.

This abrupt transition from small-celled autumn wood to large-celled spring wood creates the distinct, macroscopically visible boundaries of the annual growth rings.

Cambium. The cambium layer consists of characteristic rectangular cells stacked in radial rows.

Phloem. In cross-section, the phloem regions form trapezoids that widen toward the cambium and taper toward the periphery. Under high magnification, it is evident that the tangentially stretched layers of lignified tissue consist of densely packed sclerenchyma cells. The walls of these cells are heavily thickened, and the cell lumen is nearly obliterated, appearing as a tiny dot. These sclerenchymatous layers are known as bast fibers. Between the layers of bast fibers, referred to as hard bast (or thick-walled bast), lie the remaining phloem elements, termed soft bast (or thin-walled bast).

The sieve tubes of linden possess inclined sieve plates; consequently, in cross-section, the entire sieve plate is not visible, only segments appearing as dark spots. They can be identified by their relatively large size and the absence of contents (fluid contents do not are not preserved during sectioning). Small companion cells with dense, dark contents are located adjacent to the sieve tubes. The bast parenchyma consists of small cells similar to companion cells, also containing dense protoplasm. This parenchyma is arranged in more or less regular rows around the sieve tubes.

Radial Medullary Rays. Located between the phloem sectors as light-colored wedges, the radial rays are composed of ground parenchyma. By autumn, they accumulate significant amounts of starch.

Parenchyma of the primary cortex. Outward from the secondary cortex, i.e.,

the phloem and parenchyma areas deposited by the cambium, lie the layers of the primary cortex: the starch sheath, parenchyma, and collenchyma. The parenchyma consists of

large, living cells elongated in the tangential direction, featuring prominent intercellular spaces. Druses are present in many cells.

Collenchyma. The outermost layer of the primary cortex is formed by lamellar collenchyma. The collenchyma cells are significantly smaller than the parenchymal cells and stand out due to their glossy white walls. The tangential cell walls are thickened. Collenchyma cells are rich in contents observed in thinner sections of the cut. Chloroplasts can be distinguished within the collenchyma cells.

Protective tissue. Remnants of the epidermis are preserved on 2–3-year-old branches. The Role of the protective tissue is performed by the periderm, which develops beneath the epidermis.

Branches of woody plants (trees and shrubs) differ from herbaceous shoots by having a periderm that has replaced the epidermis, as well as by the presence of annual growth rings of wood (if the branch is more than 1 year old).

Anatomy of the Garden Parsley Root

In the center of the parsley root lies a diarch primary xylem, opposite the projections of which are two primary radial rays. To the right and left of the primary xylem strip lies the secondary xylem, traversed by wide secondary radial rays. The cells of the Primary and secondary radial rays are living and non-lignified. The secondary xylem contains large and small vessels, interspersed with parenchymal tissue.

External to the secondary xylem lies a cambium ring, followed by a highly developed secondary phloem containing groups of sieve tubes with companion cells and bast parenchyma. Wide radial rays are also distributed here radially. The bast parenchyma and radial rays serve as storage sites for nutrient reserves in the root.

Exterior to the phloem lie large cortical parenchyma cells, followed by a narrow periderm ring. Scattered throughout the phloem and cortex are essential oil canals surrounded by epithelial cells.

Due to the highly developed phloem (bast) region where nutrient reserves are stored, the anatomical structure of the garden parsley root classifies it as a carrot-type root vegetable.

A thickened root that stores nutrient reserves in its phloem region is also characteristic of the dandelion (Taraxacum officinale).

In the root of Secondary structure of black henbane, the secondary xylem is highly developed, featuring numerous radial rays, wood parenchyma, and groups of vessels and tracheids. Smaller cells with more thickened cell walls in the secondary xylem are located closer to the cambium. In the secondary phloem, situated external to the cambium, the radial rays consist of tightly packed, thin-walled, flat cells. The primary xylem is diarch.

Fig. 6. Cytology/practical/72.html">Cross section of a parsley root:

1 — periderm; 2 — essential oil canal surrounded by epithelial cells; 3 — bast parenchyma; 4 — sieve tubes with companion cells of the secondary phloem; 5 — cambium; 6 — Vessels of the secondary

xylem; 7 — wood parenchyma; 8 — secondary medullary ray; 9 — primary xylem; 10 — secondary xylem; 11 — secondary phloem; 12 — cortical parenchyma

Aerial Roots

Aerial roots are characteristic of many epiphytic plants (such as orchids, aroids, bromeliads, etc.). The structure of these roots is primary, but it possesses distinct features. The outer layers of the cortex are formed by dead cells with spiral wall thickenings. These cells are highly hygroscopic and readily absorb atmospheric moisture. Beneath the dead cells lies the exodermis, whose cells also feature thickened walls. Underneath the exodermis are thin-walled cells of the cortical parenchyma with intercellular spaces. The endodermis is not detected. The central cylinder contains the pericycle and a radial vascular bundle with polyarch xylem. The central part of the cylinder is filled with sclerenchyma cells whose walls are uniformly thickened and lignified. Ontogenetically, aerial roots are adventitious and modified. In some epiphytic plants, the adventitious aerial roots are covered by several layers of dead cells. This is the so-called velamen, which absorbs moisture from the atmosphere not via an osmotic pathway, but rather by capillary action.

Fig. 7. Structure of orchid aerial roots:

a — general appearance of the plant;

b — cross section through an aerial root;

c — portion of the aerial root in cross section under high

magnification;

1 — velamen;

2 — endodermis;

3 — cortical parenchyma;

4 — phloem;

5 — pith of the central cylinder;

6 — xylem vessels;

7 — sclerenchyma cells;

8 — passage cell of the endodermis

Haustoria of Parasitic and Semi-Parasitic Plants

In parasitic plants, true roots are replaced by specialized modified roots known as haustoria. Structurally, they are adventitious in origin. Initially, the haustoria of a parasitic plant appear on the stem epidermis as a small outgrowth. After this outgrowth penetrates the epidermis and enters the stem or root cortex, true haustoria develop, originating from the parenchyma of the parasite's stem.

In such parasitic plants as dodder (Cuscuta), broomrape (Orobanche), and others, The process of haustorial penetration begins with the secretion of specific organic acids,

which dissolve the cuticle and epidermal cells of the host plant. Pushing apart the cortical parenchyma cells of the host, the epidermal cells of the parasite grow deep into the cortex toward the vascular bundles. Consequently, the cortical parenchyma and vascular bundles of the parasite also grow toward the conductive bundles of the host. The cells that penetrate the host plant are called haustoria, which collectively form the haustorial root system.

The semi-parasitic plant mistletoe also develops a system of haustoria within the host's stem, from which the green adventitious shoots of the mistletoe emerge. Its leaves are also green, allowing the mistletoe to partially feed independently. Chloroplasts are located within both its leaves and the parenchyma of the haustoria. Mistletoe establishes and germinates in the crowns of woody plants.

Fig. 8. Haustoria of European dodder (Cuscuta europaea):

a — general view;

b — haustorium and host vascular bundle magnified;

I — stem of the dodder;

II — stem of the host plant;

1 — haustorium;

2 — vascular bundle

Structure of the corn stem.

The stem of corn clearly exhibits a bundle-type structure. Externally, it is covered by an epidermis formed from the outer layer of the SHOOT apex tunica. Beneath the epidermis lies a thin layer of chlorophyll-bearing parenchyma of the primary cortex. The central cylinder begins with sclerenchyma of pericyclyl origin. In places, the sclerenchyma interrupts the chlorophyll-bearing parenchyma and tightly

abuts the epidermis. There is no clear demarcation between the primary cortex and the central cylinder in the stem; the pith and pith rays are distinct.

The greater part of the corn stem is filled with numerous closed collateral bundles, as they are formed solely by procambium and lack secondary thickening capabilities. Each bundle is surrounded by a ring of mechanical tissue—sclerenchyma. The phloem of the bundle is oriented toward the periphery of the stem, while the xylem faces the center. The bundles are scattered haphazardly throughout the entire stem, including the pith, and are isolated from one another by parenchymatous tissue.

The chaotic arrangement of vascular bundles in the corn (maize) stem is explained by the fact that it contains not only permanent stem bundles, but also A large number of leaf traces.

Leaf traces (one or several), located at the Base of the leaf and at its point of attachment, penetrate through the leaf gap into the stem, forming the so-called leaf trace. The latter can be single-, double-, triple-, or multi-bundle. Upon entering the stem, it does not immediately descend vertically, as in dicotyledons, but extends deep into the center and curves outward, describing an arc. Therefore, in a cross-section, the leaf trace is observed at varying distances from the periphery of the stem. This type of leaf trace course is called the palmate type.

The bundles of the leaf trace converge with the vascular bundles of the lower leaves and fuse with them. The extent of a trace is measured from the base of the leaf to the level of its fusion with the Vascular Tissues of older bundles. Sometimes this fusion occurs rapidly, but often the leaf trace bundles pass through one, two, or several internodes in the stem while retaining their individuality.

A cross-section of the stem reveals differences in the size of the bundles and the structure of their individual parts—the phloem and xylem. This difference is caused by the asynchronous formation of vascular bundles at any given level of the stem, as well as the fact that some bundles represent single leaf traces, while others represent a combination of them. Some bundles are larger, while others are smaller. The larger bundles are located near the center, meaning they are older. They comprise a complete complex of protophloem and protoxylem, as well as metaxylem and metaphloem. Smaller bundles are located near the periphery, but they feature a thicker mechanical sheath.

In younger bundles, the first xylem elements to appear are scalariform, pitted, and reticulate-pitted vessels, i.e., metaxylem. This is explained by the fact that when young bundles of a particular internode appear among the older ones due to The Development of new leaves, the latter have already formed metaxylem, which will serve as the conducting tissue in the young bundles.

In corn, the number of bundles in the stem increases due to traces passing through a greater number of internodes, an increase in the number of traces, or both simultaneously. In a mature corn stem bundle, there are no cells capable of division. It consists of phloem, where sieve tubes and companion cells are arranged in a "net-like" pattern, and xylem, which includes proto- and metaxylem vessels, wood fibers, and wood parenchyma. This is a collateral closed vascular-fibrous bundle.

Fig. 9. Part of a cross-section of a corn stem:

1 - epidermis;

2 — sclerenchyma;

3 - parenchyma;

4 - vascular bundle;

5 - xylem;

6 - phloem

Structure of the asparagus (Asparagus officinalis) stem.

The epidermis covering the stem is thin, single-layered, with Stomata; its cells are tightly appressed and covered with a cuticle on the outside. Beneath it lie two to three layers of chlorophyll-bearing parenchyma of the primary cortex, which terminates in the endodermis; its cells are rich in starch grains. The central cylinder begins with a fairly thick layer of pericyclic sclerenchyma that completely surrounds the stem. The sclerenchyma cells have uniformly thickened, lignified walls.

Beyond the sclerenchyma lies the fundamental parenchymal tissue, where vascular bundles are scattered: the peripheral ones are smaller and more densely packed, while the central ones are larger and located at some distance from one another. There are no bundles in the center of the stem.

The vascular bundles are collateral and closed. Their phloem is always directed toward the periphery, and the xylem toward the center. There is no sclerenchymatous

sheath around the bundles; therefore, they—especially the outer ones—are indistinctly demarcated from the ground tissue, though its cells become smaller right next to the bundles.

The stem structure of Solomon's seal (Polygonatum odoratum) is similar.

Fig. 10. Stem of asparagus (Asparagus officinalis):

a — cross-section of the stem; b — anatomical structure of a part of the stem;

1 — epidermis;

2 — primary cortex;

3 — sclerenchyma;

4 — vascular bundles;

5 — starch sheath (endodermis);

6 — pith;

7 — stomate;

8 — stem parenchyma;

9 — wood parenchyma;

10 — annular and spiral vessels;

11 — reticulate vessels;

12 — phloem sieve tubes

Structure of the "Straw" Type Stem

In the stems of most grasses, the internodal parenchyma breaks down during growth, forming a large central cavity. A specialized stem type—the straw—develops, featuring hollow internodes and nodes filled with parenchyma, where the vascular bundles coming from the leaf, axillary buds, and

upper internodes converge. Examining a hollow stem (e.g., wheat or rye) in cross-section reveals: the epidermis, areas of subepidermal sclerenchyma and chlorenchyma, stomata, and closed collateral vascular bundles. On the inner side, the sclerenchyma ring borders a large-celled parenchyma whose cells die off by the end of the vegetative season.

The vascular bundles are pushed toward the periphery and appear to be arranged in two circles: one lies closer to the epidermis, consisting of smaller bundles situated between patches of chlorenchyma; the other lies within the parenchymatous tissue, consisting of larger bundles.

The structure of the vascular bundles is identical to that in corn stems: the phloem is located closer to the epidermis and consists of sieve tubes with companion cells, while the xylem faces the center and comprises vessels, wood fibers (libriform), and wood parenchyma. Each bundle is surrounded by a mechanical sheath of sclerenchyma.

The stem structure of grasses exhibits A number of adaptive features that ensure their upright posture and mechanical stability.

Fig. 11. Structure of the durum wheat stem (cross-section):

a — diagram; b — section of the stem;

1 — epidermis;

2 — sclerenchyma;

3 — chlorenchyma;

4 — collateral vascular bundles;

5 — stem cavity;

6 — phloem;

7 — parenchyma;

8 — mechanical bundle sheath;

9 — xylem

Pine needle.

Examination of the transverse section of a needle reveals a slightly flattened central vascular cylinder surrounded by an endodermis with Casparian strips. Within the cylinder, two vascular bundles surrounded by parenchyma are visible; one of the parenchymatous

cells features bordered pits and serves for water conduction, while the others contain starch. Sclerenchyma cells are discernible between the bundles. Surrounding the endodermis is the assimilation tissue—folded mesophyll—whose cell walls project deep into the cells with numerous folds, thereby increasing their surface area.

A high density of chloroplasts is arranged along the cell walls, with a Nucleus clearly visible in the center of each cell. Closer to the surface, the folded parenchyma is permeated by resin ducts, which appear as rings in cross-section; on the inside, they are lined with resin-producing epithelial cells, while on the outside, they are reinforced with thick-walled (non-lignified) sclerenchyma.

Directly beneath the epidermis lies a layer of cells with thick walls resembling those of sclerenchyma, known as the hypodermis (meaning "subcutaneous layer"). The epidermis consists of cells that appear nearly square in cross-section, with thickened walls such that their cell lumens are almost obliterated. Four pore canals extend from the center of each cell toward the corners. The epidermis is covered externally by a thick layer of cuticle. Over time, the needle's epidermis undergoes lignification, as do the walls of the guard cells. The stomata in pine are deeply sunken, meaning they reside within depressions.

Beneath the hypodermis, numerous schizogenous resin ducts are arranged in a circle, surrounded by sclerenchyma and extending along the axis of the leaf. In the center of the leaf lie one to three vascular bundles featuring a sclerenchymatous sheath, a thick-walled starch-storing endodermis, and transfusion tissue in the center. The bundles are open, with the xylem facing the adaxial side and the phloem facing the abaxial side.