The heartwood of coniferous trees (pine) has a rounded shape with irregular radial processes. It consists of fairly large parenchyma cells, shaped like polyhedra with thin lignified walls; In old trees, these cells are dead, their cavities are filled with air. The core is surrounded by elements formed in the first year of growth that make up the primary wood. The pith, together with the adjacent primary wood, is called the pith tube. Coniferous wood is distinguished by its comparative simplicity and regularity of structure. It consists of only two main elements: tracheids perform conducting and mechanical functions, and parenchyma cells perform storage functions. In Fig. Figure 16 shows a three-dimensional diagram of the microscopic structure of wood of a typical coniferous species - pine.
Tracheids are the main element of coniferous wood. They occupy over 90% of the total wood volume. Tracheids have the shape of highly elongated spindle-shaped cells (fibers) with thickened lignified walls and obliquely cut ends. On a cross section, the tracheids are arranged in regular radial rows. The shape of the tracheids in cross section is close to rectangular. Tracheids are dead elements; in the trunk of a growing tree, only the newly formed (last) annual layer contains living tracheids, the death of which begins in the spring, gradually increases by autumn, and by the end of winter all tracheids of the last annual layer die off.
Rice. 16. Scheme of the microscopic structure of pine wood: 1 - annual layer; 2 - core beam; 3 - vertical resin passage; 4 - early tracheids; 5 - late tracheids; 6 - bordered pore; 7 - ray tracheids; 8 - multi-row beam with horizontal resin stroke.
Within one annual layer, the tracheids of the early and late zones are very different from each other. Early tracheids. formed at the beginning of the growing season, they perform conducting functions (conduct water), therefore they have a wide internal cavity and thin walls with numerous pores. Early trache size the id in the radial direction is greater than in the tangential direction; the ends of the tracheids are slightly rounded. Late tracheids, deposited by the cambium in the second half of the growing season, are mechanical elements, therefore their walls are greatly thickened due to a sharp decrease in the internal cavity; the ends of the late tracheids are strongly pointed (Fig. 17). The total number of bordered pores in early wood of spruce tends to increase in the direction from the bark to the core, while in fir it is the opposite. However, the number of closed pores in the wood of both species increases in the direction from the bark to the core, and the most sharp, abrupt increase in their number is observed during the transition of sapwood to mature wood. At the same time, it was noted that in the late tracheids of the pine kernel there are significantly fewer closed pores than in the early ones (according to some data, 8 times), due to which the late zone of the annual layers is saturated with antiseptics better than the early one. The size of tracheids and the thickness of their walls in the same trunk increases in the direction from the core to the bark until a certain age (different for different breeds), after which they remain unchanged or decrease slightly. The diameter of early pine tracheids reaches a maximum at 40 years of age and subsequently remains almost unchanged. Along the height of the trunk of mature trees, the length and width of the tracheids in the same annual layer gradually increases from the base of the trunk to the crown, and within the crown they quickly decrease as they approach the top; The thickness of the tracheid walls, on the contrary, first decreases, and in the crown area increases slightly again. In branches, tracheids are smaller than in the trunk; branches that arise from the trunk where the tracheids are longer also have longer tracheids. Growing conditions influence the size of pine tracheids in the Bryansk region; it turned out that the largest early tracheids and the thickest-walled late tracheids are observed under average, optimal for pine, growing conditions (grade I-II); improvement (grade I a) and deterioration (grade IV) of growing conditions are accompanied by a decrease in the size of early tracheids and the wall thickness of late tracheids. Growing conditions influence mainly the thickness of the walls of late tracheids. and the thickness of the walls of early tracheids remains almost unchanged. Parenchyma cells in the wood of all conifers make up the pith rays, resin ducts (in some conifers) and, in some species, the wood parenchyma. The medullary rays of coniferous species are very narrow (single-row in cross section), and their height consists of several rows of cells. In pine, cedar, larch and spruce, the medullary rays consist of two types of cells: the upper and lower rows along the height of the ray are represented by horizontal (or ray) tracheids with small bordered pores and characteristic thickening of the walls in some conifers; the internal, i.e., medium in height, rows consist of parenchyma cells with simple pores (see Fig. 17). The medullary rays of fir, yew and juniper consist only of parenchyma cells. The parenchyma cells of pine and cedar rays are equipped with one or two large simple pores, while in the rest of our coniferous species these cells have three to six small simple pores. Pine, cedar, larch and spruce, in addition to single-row rays, also have multi-row rays through which horizontal resin passages pass. Ray tracheids are dead elements; the parenchyma cells of the ray remain alive throughout the sapwood, and sometimes in the core, i.e. for 20-30 years. In a growing tree, nutrients and water move horizontally along the pith rays during the growing season; During the dormant period, reserve nutrients are stored in them. Water with dissolved sodium phosphate, containing the radioactive phosphorus isotope P 32, passes through the medullary rays of coniferous and deciduous trees. The resin duct is a narrow long intercellular channel filled with resin, formed by parenchyma cells. Resin passages (vertical and horizontal) from our conifers are pine, spruce, larch and cedar; A number of other conifers (fir, yew, juniper) do not have resin ducts in the wood. Rice. 18. Vertical resin ducts on a cross section of pine and larch wood: a - freed from resin in pine wood: b - filled with resin in pine wood; c - in larch: 1 - lining cells; 2 - dead cells; 3 - cells of the accompanying parenchyma; 4-channel travel; 5 - tracheids; 6 - core beam. Vertical resin ducts in pine are formed by three layers of wood parenchyma cells: the inner layer; ring of dead cells and outer layer. The inner layer, or epithelium, of the pine resin duct consists of lining cells that look like thin-walled bubbles that protrude into the resin duct channel to varying depths. When the stroke is filled with resin under high pressure, they become flat, and when the stroke is emptied, they protrude into the channel until they come into contact with each other (Fig. 18). The lining cells of the pine tree have thin cellulose walls and are filled with thick granular protoplasm with a large nucleus; it is these cells that secrete resin. In spruce and larch, the membrane of the lining cells thickens and becomes woody, as a result of which they probably lose the ability to squeeze resin out of the passage. A ring of dead cells, devoid of protoplasm and filled with air, surrounds the epithelium of the resin duct. The outer layer is represented by living cells of the accompanying parenchyma with a nucleus, thick protoplasm and reserve nutrients (starch, oil). The length of the lining cells in longitudinal sections of wood is slightly greater than the transverse dimensions, the dead cells are narrow and long, and the accompanying cells are several times longer than the dead ones and much wider than them. The lumen (channel) of the vertical resin passage in the tangential direction usually corresponds to four rows of tracheids. With age, the diameter of the vertical resin ducts increases in the direction from the core to the bark. In the wood of Siberian larch, vertical resin ducts are formed by only one row of lining cells; there is no layer of dead cells, and accompanying cells are rare or absent. If a growing tree is damaged, the number of resin ducts may increase. Horizontal resin ducts run along the medullary rays (Fig. 19) and are usually formed by only two layers of cells: the epithelium and the layer of dead cells. The length of horizontal passages increases with age as wood and bast grow; their outer end, located in the phloem, is closed by the proliferation of lining cells. The diameter of horizontal resin passages is on average 2.5-3 times less than the diameter of vertical passages. In pine the diameter of horizontal passages is 36-48 μ, in Siberian cedar 48-64 μ, in spruce 20-32 μ, in larch 24-48 μ; per 1 mm 2 of the surface of the tangential section in pine, spruce and cedar there are from one to three, and in larch from one to four resin passages. Horizontal resin passages intersect with vertical ones (see Fig. 19), forming a single resin-bearing system. Rice. 19. Resin ducts and cambium cells: a - horizontal resin duct in the core ray of pine; b - connection of vertical and horizontal resin ducts on a tangential section of wood; c - shape of cambium cells (diagram); 1 - lining cells; 2 - dead cells; 3 - horizontal stroke channel; 4 - vertical stroke channel; 5 - shape of cambium cells in a tangential section (single and gable); 6 - on the radial; 7 - on cross sections. The number of connections between vertical and horizontal passages reaches several hundred per 1 cm3. From this system of connected resin passages, the passages of the nucleus are switched off, which cease to function as living cells die; The passage channels in the pine are filled with outgrowths of lining cells. However, in the core of Siberian larch, a large number of resin passages remain open (their channels are not filled). Wood parenchyma is rare in conifers. Parenchyma cells, somewhat elongated along the length of the trunk, are often connected in rather long rows running in the wood parallel to the axis of the trunk. Among our coniferous species, pine and yew do not have woody parenchyma. The approximate content of various elements in coniferous wood is given in table. 5. Table 5. Content of various elements in coniferous wood. medullary rays resin passages wood parenchyma Pine (different types) Spruce (different types) Western larch Liarsuga Red cedar Sequoia evergreen In addition to highly elongated cells that form the fibrous elements of wood and bark, scattered accumulations of small cells such as parenchyma are observed, which form the medullary and bast rays. Located at the border between wood and bark, the cambium covers the entire wood of the tree with a continuous mantle. The activity of the cambium determines the growth of the tree in thickness. As they grow, the cambial cells elongate slightly along the radius of the trunk and are divided by tangential septa. One of the resulting cells remains cambial, and the other goes to the formation of wood or bark elements. Cell division towards the wood occurs 10 times more often than towards the bark, as a result of which the wood grows much faster than the bark. The cambium works throughout the life of the tree, that is, sometimes hundreds and even thousands of years (sequoia); Moreover, its activity in temperate climates manifests itself periodically: it freezes for the winter and resumes in the spring, resulting in layering of the wood (the formation of annual layers). The activity of the cambium in the spring begins first in the thin parts of the trunk and branches, spreading down the trunk, then passes into the roots, first thick and then thin; the end of cambium activity in autumn occurs in the same order. Goal of the work:
study the anatomical structure of Scots pine needles and the rhizomes of common bracken fern. Required materials and equipment:
microscopes, permanent preparations, herbarium specimens. Tasks:
1. Consider a cross section of a leaf (needles) of Scots pine ( Pinus sylvestris L.) at low and high magnification microscope. Draw a diagram of the structure of a cross section of a needle at low magnification, noting the hypodermis, resin canals, mesophyll, endoderm, vascular bundles, and transfusion tissue. At high magnification, sketch a section of the cross section, on which to designate the mesophyll, endoderm, hypodermis, epidermis, and resin canal. 2.
Examine a cross section of a bracken rhizome ( Pteridium aquilinum(L.) Kuhn.) at low and high magnification microscope. Draw a cross-section diagram at low magnification, noting vascular bundles, areas of mechanical tissue, and the zone of outer and inner cortex. At high magnification, sketch the vascular bundle, showing the endoderm, pericycle, phloem and xylem.
Leaf structure of Scots pine
The leaves are needle-shaped and arranged in groups of 2 on short shoots. The cross-section of the leaf is semicircular, its upper side is flat, and its lower side is convex. On the outside is the epidermis, consisting of almost square cells covered with a layer of cuticle. The walls of the epidermal cells are very thickened and lignified. As a result of thickening, only a small cavity remains inside the cells, from which narrow pore channels extend diagonally to the corners. Under the epidermis is a one- or two-layer hypodermis, consisting of flattened cells with evenly thickened walls. At the level of hypodermal cells, stomatal guard cells with lignified walls are visible. Under the hypodermis layer, resin canals are visible, lined with thin-walled epithelial cells and surrounded by a lining of thick-walled cells. In the center of the leaf there is a conducting system, which consists of 2 collateral bundles, connected by mechanical tissue and surrounded by transfusion tissue (serves to move water and solutions of organic substances from the bundles to the mesophyll). Outside the conducting system is a single-row endoderm. Mesophyll consists of cells of unusual shape: they have numerous folds that appear as a result of the invagination of the membrane into the cell, which serves to increase its surface. The structure of the bracken rhizome
The long horizontal rhizome of bracken is located at a depth of 20-40 cm underground. The roots of the bracken are black and extend downwards from the rhizome. The rhizome itself has a polycyclic structure ( rice. 71). In a cross section, two large oval vascular bundles are clearly visible in the center. Around them are two half-rings of mechanical fabric. Behind it are small round bunches, among which one large oval one is usually visible. The bundles are immersed in parenchymal tissue, where the inner and outer cortex are clearly visible. The outside of the stem is covered with epidermis. Numerous small tufts are visible in the bark, also extending into the leaves. Bracken bundles are closed; they are delimited from the bark by endodermis with passage cells. Next is the pericycle, then the phloem, in which sieve tubes and bast parenchyma are visible. In the center of each bundle is xylem. Questions about the material covered:
1. Describe the features of the anatomical structure of leaves. 2. Describe the features of the anatomical structure of rhizomes. 3. Describe the features of the anatomical structure of plants from various ecological groups (hydrophytes, hygrophytes and xerophytes; heliophytes - sciophytes; succulents - sclerophytes). Examine the finished microspecimen “Pine needles” in a cross section at low magnification of the microscope, mark the location of the tissues; the presence of two conductive bundles, which are united by a complex of mechanical fibers, surrounded by transfusion tissue and endoderm; mesophyll uniformity; hypodermis, located under the epidermis; resin passages. Using a high magnification microscope, examine the features of cells in all tissues. Draw a diagram of the structure of a leaf on a cross section, indicate its structure. Description of object: Pine leaf (needles)
mperennial, with a xeromorphic structure, the structure of which is determined by sharp fluctuations in temperature throughout the year and insufficient water supply in winter. The reduction of the evaporating surface is achieved by the needle-shaped leaves. In cross section, the pine leaf is semicircular: morphologically, the upper side of the leaf is flat, the lower side is convex. On the outside there is a thick cuticle, under which lies the epidermis. Its cells are small, square in shape, with very thick membranes. The cavities of epidermal cells are round, with narrow pore canals extending to the corners of the cells. The stomata are located over the entire surface of the needles, they are buried, their guard cells are located at the level of a single-layer hypodermis of thick-walled cells with lignified membranes, under the parostomatal cells. The thickened shells of the guard and parastomatal cells are lignified. The mesophyll is folded, homogeneous, with small intercellular spaces. Due to the growths of the cell membrane, the surface of the wall layer of the cytoplasm containing chloroplasts increases. The mesophyll contains schizogenic resin ducts. They run along the leaf and end blindly near the apex. The outside of the resin channel is lined with thick-walled fibers. Its cavity is lined with thin-walled living cells of epithelial tissue that secrete resin. The conducting system is represented by two collateral closed bundles located in the center at an angle to each other. The xylem faces the flat side of the leaf, the phloem faces the convex side. Between the bundles in the lower part there are fibers with lignified shells. The vascular bundles are surrounded by transfusion tissue, which consists of two types of cells. Some cells are elongated, with lignified membranes and bordered pores (transfusion tracheids), others are living, thin-walled, parenchymal, often containing resinous substances and starch grains. Transfusion tissue is involved in the movement of substances between vascular bundles and mesophyll. Conducting bundles with transfusion tissue are separated from the mesophyll by the endoderm - a single-row layer of parenchyma cells with Caspary spots on the radial walls. Rice. 27. Diagram of a cross section of Scots pine needles (Pinus
sylvestris
L.):
1 – epidermis with stomata, 2 – hypodermis, 3 – schizogenic resin canal, 4 – folded mesophyll, 5 – endoderm, 6 – collateral vascular bundle, 7 – phloem, 8 – xylem, 9 – sclerenchyma, 10 – transfusion tissue, 11 – cuticle. Conclusions:
_____________________________________________________________________________ ______________________________________________________________________________________ Conifers are the oldest existing plants on our planet. Their age is estimated at hundreds of millions of years. Evolution has had virtually no effect on the anatomical structure of needles and cones. When comparing the leaves of conifers, which are popularly called needles, with the leaves of flowering plants, one can notice that while the needles are relatively uniform, they have different shapes, sizes, colors, and in some species they do not look at all like ordinary needles. The needles look like narrow needle-like leaves. It is characterized by the presence of a dense skin, which is covered with a waxy substance. This is necessary to reduce the evaporation of moisture by gymnosperms. For example, spruce needles are tetrahedral, but often the edges are almost invisible, and the needles look flattened. Drawing. Cross section of Scots pine needles
If you cut a needle, it has the shape of an irregular diamond, with the flattest angle directed downwards. This is where the midrib of the leaf is located. Along the other edges of the needle, white stripes are visible, formed by stomata - respiratory openings through which plant respiration occurs. Stomata also serve to evaporate moisture, which the tree absorbs from the soil even in severe cold. This explains the fact that spruce, like other conifers, cannot be replanted in the autumn, since the roots cannot take root firmly, and water practically does not rise up the stem to the needles, although respiration occurs in the same mode. An important difference between conifers and deciduous trees is that their petiole is firmly connected to the branch and remains on it, even after the needle dies. The needles fall off after 6-7 years. They are well protected from the effects of adverse environmental factors by a thick layer of waxy coating - the cuticle. Moreover, in many species the coating is so thick that the needles acquire a blue tint. Their seeds are attached directly to the seed scales, and those that are collected into female cones are equipped with special wings. Leaving the cone, they glide on their wings, resembling small helicopters when rotating. This helps them move away from the mother plant. The appearance of conifer cones is varied and specific. They may differ in length, shape, placement in space, color, structure and shape of sporophylls, method of seed dispersal, etc. But the fundamental structure of the cones is the same. All cones at the base have an axis, which is separated from the vegetative part of the tree and is a short shoot with spore-bearing leaves located on it - sporophylls. There are female and male cones. The vast majority of conifers are monoecious. They have both female and male cones developing on the same plant. In most cases, male cones are concentrated in groups in the axils of the leaves, sometimes on the tops of the side shoots. Female cones are distinguished by a compact arrangement, occasionally they are located singly. Related materials: Completed by: O.M. Smirnova biology teacher Municipal educational institution Urenskaya secondary school
1. Consider the external structure of a pine shoot. How are the needles located on the shoot? What is the appearance of the needles? 2. Consider the external structure of the spruce shoot. How are the needles located on the shoot? How does the appearance of spruce needles differ from pine needles? 3. Examine the microscopic specimen “Pine needles” under a microscope at first 56 and then 300 times magnification. On a cross-section of the needles, find the dense skin covering the outside of the needles and the stomata in the recesses. Count the number of stomata. 4.Why do pine needles evaporate a lot of moisture?
Pine is a perennial plant reaching a height of 30-40m. The lower parts of the trunks are devoid of branches. In old pines, the first branches begin at a level of at least 10 m from the ground. Pine is very light-loving. Therefore, its lower branches die off quite early. It cannot grow or renew itself under the canopy of other trees. The needle-shaped leaves of pine - needles - reach 3-4 cm in length. The needles are arranged in twos on very shortened shoots. During the winter, pine needles, like most coniferous trees, do not fall off, but remain on the plant for 2-3 years. The needles fall off along with the shortened stems. The needles are covered with thick skin. There are few stomata, they are arranged in rows and are located in recesses. There are only two vascular bundles in the leaf, and they do not have lateral branches. Due to these characteristics, pine evaporates moisture economically and easily tolerates drought. The leaves also ate needles, but they were much shorter and more prickly.
Rice. 17. Tracheids and medullary rays: a-early wood; b - late; pine tracheids from above; medullary rays in a radial section under a microscope (bottom); on the left - pine trees; on right -fir; 1 - ray tracheids with small bordered pores; 2 - parenchyma cells with simple pores (large in pine and small in fir). Between the typically early tracheids at the beginning of the annual layer and the typically late tracheids at the end of the layer there are several rows of tracheids, which in terms of the thickness of the shells and the size of the cavity occupy an intermediate position between the early and late tracheids. Such a layer of intermediate tracheids was observed in pine and larch wood. The width of early pine tracheids in the radial direction is on average 40 μ, of late ones - 20 μ; the thickness of the walls of early tracheids is 2 μ, of late ones - from 3.5 to 7.5 μ. The width of early tracheids of spruce from the Arkhangelsk region is on average 45 μ, of late ones - 22 μ; thickness of the walls of the early trachea id about 3 μ, late - about 5 μ. The length of pine tracheids ranges from 2.1 to 3.7 mm, spruce tracheids - from 2.6 to 5 mm; Moreover, the length of late tracheids is approximately 10% longer than the early ones. In most of our coniferous species, the walls of the tracheids are smooth and only in the yew they have clearly visible spiral thickenings. The thickness of the pine tracheid shells during the transition to the late zone first increases, reaching a maximum, and then decreases near the boundary of the annual layer. Thus, the thickest-walled tracheids are not located at the boundary of the annual layers, but in its third quarter. A characteristic feature of tracheids is bordered pores, located mainly on the radial walls at the ends of the tracheids, with which each tracheid is wedged between neighboring ones, forming a tight connection. Typical bordered pores are present on the walls of early tracheids; late tracheids have smaller pores and in significantly fewer numbers. One early pine tracheid has an average of 70 pores, one late tracheid has only 17 pores; on the tracheids there were 90 and 25 pores, respectively, on the trachepda of European larch - 90 and 8 pores. The diameter of the bordered pores in different rocks ranges from 8 to 31 μ, the diameter of the hole - from 4 to 8 μ. Membrane of bordered pores in the trachea Coniferous ides have in the peripheral non-thickened part small through perforations of oval or round shape, facilitating communication between tracheids. When the membrane is deflected in one direction or another, the torus closes the pore opening, as a result of which the passage of water through it is greatly hampered. In sound and mature coniferous wood, the bordered pores are essentially excluded from action and therefore such wood becomes impermeable to water. 
The cambium consists of a continuous row of narrow, radially flattened, strongly elongated living cells along the length of the stem with wedge-shaped pointed ends. Cambium cells reach the greatest length in coniferous species. In deciduous species, the length of cambium cells ranges from 0.15 to 0.6 mm and exceeds the transverse dimensions by several tens of times, and in conifers it can reach 5 mm and exceeds the transverse dimensions by several hundred times. The cells contain densely granular protoplasm with a spindle-shaped nucleus. The shape of cambium cells in three sections is shown schematically in Fig. 19.
For pine needles ( rice. 70), like the perennial leaves of other conifers, are characterized by a xeromorphic structure, the development of which is caused by sharp changes in temperature throughout the year and the need to reduce evaporation in the winter, when the water supply is insufficient.
Conifers do not have true fruits and flowers. They belong to the division of gymnosperms.
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