Cross section of needles. Pine needles under a microscope. The anatomical structure of a coniferous leaf
Examine the finished micropreparation "Pine needles" on a cross section at low magnification of the microscope, note the location of tissues; the presence of two conductive bundles, which are united by a complex of mechanical fibers, surrounded by transfusion tissue and endoderm; mesophyll homogeneity; hypodermis, located under the epidermis; resin passages.
At high magnification of the microscope, consider the features of the cells of all tissues.
Draw a diagram of the structure of a leaf on a cross section, indicate its structure.
Description of the object: Pine leaf (needles) mperennial, with a xeromorphic structure, the structure of which is due to 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. Outside is a thick cuticle, under which lies the epidermis. Its cells are small, square in shape, with very thick membranes. The cavities of the epidermal cells are rounded, narrow pore canals extend to the corners of the cells. The stomata are located over the entire surface of the needle, they are deepened, their trailing cells are located at the level of a single-layer hypodermis of thick-walled cells with lignified membranes, under the peristomatal cells. The thickened membranes of guard and peristomatal cells are lignified.
The mesophyll is folded, homogeneous, with small intercellular spaces. Due to outgrowths of the cell membrane, the surface of the parietal layer of the cytoplasm, which contains chloroplasts, increases. Schizogenic resin ducts are located in the mesophyll. They run along the leaf and end blindly near the top. Outside, the resin channel has a lining of 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. Xylem faces the flat side of the leaf, phloem faces the convex side. Between the bundles in the lower part there are fibers with lignified shells. Conductive 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. The transfusion tissue is involved in the movement of substances between the conductive bundles and the mesophyll. Conductive bundles with transfusion tissue are separated from the mesophyll by the endoderm, a single-row layer of parenchymal cells with Casparian spots on the radial walls.
Rice. 27. Scheme of a cross section of needles of Scotch pine (Pinus sylvestris L.):
1 - epidermis with stomata, 2 - hypodermis, 3 - schizogenic resin canal, 4 - folded mesophyll, 5 - endoderm, 6 - collateral conductive bundle, 7 - phloem, 8 - xylem, 9 - sclerenchyma, 10 - transfusion tissue, 11 - cuticle.
Conclusions: _____________________________________________________________________________
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Lecture. Sheet.
The leaf is one of the most important and specific plant organs.
Sheet(Latin folium, Greek phyllon) - lateral, flat ( dorsoventral) an organ that has limited growth and is adapted to perform the functions of photosynthesis, transpiration and gas exchange.
The shape of the leaf contributes to the creation of a maximum photosynthetic surface.
The role and main functions of the sheet.
1. Main meaning leaf consists in the fact that it absorbs solar energy, which is bound in the form of organic compounds and then used not only by plants, but also by all other organisms on the Earth. As K.A. Timiryazev noted, plants play a cosmic role, being intermediaries between the cosmos and all other inhabitants of the Earth. And the main role in this mediation belongs to the sheet. Emphasizing this, K.A. Timiryazev wrote that “the whole essence of a plant is expressed in a leaf. The plant is a leaf.
Thus, the leaf is the most important and specific organ of the plant, since it mainly occurs photosynthesis process . There are also chloroplasts in the primary bark of the stem, but there are not so many of them and the photosynthetic surface is small.
The sheet is a kind of laboratory for the synthesis of organic substances. 80% of all photosynthesis is provided by leaves.
2. Controlled evaporation of water by leaves (transpiration). Transpiration is not only a physical, but also a physiological process regulated by the leaf.
The main role of transpiration:
1) regulation of water entry into the roots and its movement through the vessels;
2) thermoregulation, protection of the plant from overheating.
Plants of forests and deserts, as a rule, evaporate more water than plants of forests, marshes, etc.
3. Gas exchange.
Additional functions:
4. mechanical function - is expressed in the fact that the soft tissues of the leaf are reinforced with reinforcing mechanical tissues located in the veins, and subsequently the stem stele is strengthened and formed due to leaf traces.
5. Reserve function not very typical for a leaf. Most often, water can be stored in the leaves (leaf succulents: aloe, agave, havortia, etc.).
6. excretory function provided by various glands located on the leaf and releasing essential oils, water, salts, etc.
7. A leaf may have specific functions during metamorphoses.
General morphological features of the leaf.
1 feature. The main difference between a leaf and a stem and root is that the leaf is not axial, but a planar organ that has large outer surface, which is necessary for the effective flow of photosynthesis, the absorption of CO 2 and light, gas exchange and transpiration.
A large outer surface of the leaf is achieved in two ways: 1) in some plants - by the large size of the leaves (banana, palm trees, Victoria Regia), 2) in others - by increasing the number of leaves (the smaller the leaves, the more of them). A large number of leaves is an adaptive property that helps plants to function normally when damaged by insects or other animals.
2. Sheet usually thin organ, because sunlight must pass freely through it for the normal course of photosynthesis.
Therefore, the thickness of the leaves depends on the lighting conditions: in shading, thin leaves are formed, in the light - thick and more dense, in water - very thin leaves (as the light is scattered).
3. Unlike the stem and root, the leaf has limited growth. The sheet is characterized only the primary building so that light can pass through the sheet ( and in the secondary structure, opaque and dense conductive and mechanical tissues are formed).
Usually the leaf does not grow long (in temperate latitudes - 1-2 weeks). An exception is amazing velwitchia (gymnosperms). Its two leaves, due to intercalary growth, grow throughout life (from several hundred to 3 thousand years).
The lifespan of a single leaf is short. Deciduous - a maximum of one season. There are also evergreens, the leaves of which live 3-5 years (for spruce - 20 years).
External leaf structure.
Despite the huge variety of leaves, they usually have 3 (sometimes 2) parts:
1.
leaf blade
Petiole
3. leaf base .
leaf blade- flattened (more often) part of the sheet.
leaf petiole- axial, stem-like, narrow part of the leaf. The orientation of the sheet in relation to the light depends on it. It can change the position of the leaf in space, which is associated with osmotic properties. Leaves with petioles are called petiolate if the petiole is absent, then the leaf is called sedentary.
leaf base- the part of the leaf with which it is attached to the stem in the region of the node. Through the base, leaf traces enter the stem.
The base of the leaf may grow:
a) paired outgrowths form on the sides of the sheet - stipules. They develop before the leaf blade and protect it for the first time during formation. Often they are green and photosynthesize. (Sometimes the stipules are very large and serve as leaf blades, which are reduced or turned, for example, into antennae in some legumes). In some plants, stipules quickly fall off, in others they remain until the leaf lives.
b) the base of the leaf grows, covers the stem, forming vagina . It serves to protect the axillary buds and intercalary meristems, and also has a mechanical function, supporting the delicate parts of the stem. The vagina can be in the form of a wide cover, open on one side (for example, in umbrella plants), or in the form of a tube, often closed (in cereals and sedges). In some plants, water accumulates in the vagina, which is then absorbed by the plant (for example, in the tropics - a tree of travelers, bromeliads).
The leaves are distinguished by a very large variety of shapes, dissection of the leaf blade, and leaf edges. (independently according to the textbook)
By venation leaves are pinnate(oak) (there is one main vein, and secondary veins of the 2nd order depart from it), palmate(maple) (several large veins fan out from the petiole, and smaller veins from them), with arc venation (plantain) and with linear(or parallel) (cereals, sedges). The ancient gymnosperm plant ginkgo and modern ferns have preserved the most primitive type of venation - dichotomous, in which each vein bifurcates, then bifurcates again, etc. This type of venation is found in all extinct and modern spore plants, as well as in a typical or modified form in gymnosperms.
According to the number of leaf blades distinguish leaves simple(with one leaf blade) and complex(with several leaf blades). In compound leaves, leaf blades are attached to a common petiole - rachis differently. There are pinnately complex (leaves sit opposite each other on the rachis) (there are paired and unpaired pinnately compound leaves) and palmately compound leaves (leaves are attached to the rachis at the top, like a fan).
The shape of the leaf is a characteristic feature of the species, however, within one individual, or even one shoot, the leaves can vary in shape and form three formations : grassroots, middle And riding. Leaves grassroots formation usually in the form of scales, brown or reddish with an undeveloped leaf blade. For example, in lily of the valley, they appear very first in spring and perform a protective function. Later, leaves of the middle formation develop on the shoot, which have a normal structure and perform the main functions: photosynthesis, transpiration and gas exchange. On the peduncles, leaves of the upper formation are formed - bracts that protect the buds.
Within the median formation, the leaves on the shoot can also vary in shape. This phenomenon is called heterophylly (diversity) . It usually manifests itself in connection with age-related changes or during the life of the plant in different environments and ecological conditions (for example, the above-water, underwater and floating leaves of the arrowhead differ not only in shape, but also in the internal structure; .; in meadow plants, the upper leaves are narrower, thicker and dissected, receive more light, the lower ones are thinner and wider, less dissected, for example, field bark).
An even more striking example of leaf differences is anisophyllia - leaves differ in shape, size and structure within one shoot node (with opposite or whorled leaf arrangement). It occurs in plants with creeping or lying shoots, leaves facing the soil are usually scaly. The aquatic fern Salvinia floating in a node has 3 leaves, two are ordinary, photosynthetic, the third is underwater, dissected and performs a suction function.
Leaf anatomy.
Anatomical structure leaf is a hereditarily fixed trait.
Leaf ontogeny.
The leaf is laid in the apex of the shoot. Tubercles of rudimentary leaves appear below the growth cone - leafy primordia . Each primordia appears after a certain strictly constant period of time - plastochron ("plastos" - decorated, "chronos" - time).
For example, an oak has a plastochrone of 2.8 days, a linden has 5 days, and a spruce has 4.3 hours. As a rule, the smaller the leaves, the shorter the plastochrone. Thanks to the plastochrone, the leaves on the plant are arranged in a strictly defined order.
Leaf growth is different from stem and root growth. 
1) A new leaf germ is laid inside the kidney in the form of a meristematic tubercle, which initially and very briefly grows with an apex (apical growth). Then the leaf primordium differentiates into upper and lower parts, which grow unequally.
2) The leaf is actively growing at the base (procambium is being formed). The base of the sheet is formed.
3) The region of the central vein grows intercalated in length, thickens and acquires a cylindrical shape (the axis of the leaf is laid).
4) On the sides of the leaf axis, a leaf blade begins to form due to the marginal (marginal) lat. Margo - edge) diffuse growth. Marginal meristems are laid in the form of rollers on the sides of the central vein and form the leaf plane. Uneven marginal growth leads to the formation of blades with an uneven edge, lobes, dissected, etc. Stipules, as a rule, form before the leaf blade (as outgrowths of the leaf base) and protect it from damage.
5) At the last stage, the petiole grows. It appears after the leaf blade finishes its growth. The petiole grows in length due to intercalary (intercalary growth) and in a certain way orients the leaf in relation to the light.
Anatomy of a typical leaf.
In leaf anatomy, the connection between the anatomical structure and the functions performed is clearly traced: photosynthesis, transpiration and gas exchange.
Anatomical differences between leaves and stems.
1) The sheet is dominated parenchymal tissue, but not a storage parenchyma, but a highly specialized assimilation parenchyma, whose cells contain chloroplasts.
2) There are few conductive and mechanical tissues, they form veins sheet.
3) Many intercellular spaces (associated with gas exchange function).
4) Various excretory tissues can be developed.
The leaf has only the primary structure!
1. Outside, the sheet is covered with primary integumentary tissue - epidermis. On the leaf, the epidermis has its most typical structure. A powerful cuticle layer protects against excessive evaporation of water (in plants of humid habitats, the cuticle is thin or absent), as well as trichomes of various structures. There are a lot of stomata. Most of the stomata are on the underside of the leaf. This is explained by the fact that 1) with open stomata on the upper side of the leaf, a lot of water would be lost; 2) the main source of CO 2 is the soil, where organic matter decomposes and carbon dioxide enters the atmosphere. It is heavier than air and accumulates usually in its lower layers. Since carbon dioxide rises from the bottom up, the location of the stomata on the underside contributes to its speedy entry into the leaf along the shortest path.
Sometimes stomata can be evenly distributed on both sides of the sheet if the leaves are located edge to the sun (in a number of plants of savannahs, deserts, in eucalyptus - tree without shade).
Only on the top side of the sheet stomata are located in aquatic plants with leaves floating on the surface of the water. Leaves completely submerged in water have no stomata.
Number of stomata- an average of 1 mm 2 - 250 stomata.
In some plants (usually growing in arid climates), under the epidermis there may be a hypodermis (colorless), the cells of which perform a water storage, less often a mechanical function (for example, in conifers).
2. Leaf mesophyll is a highly specialized assimilation tissue of the leaf.
In most flowering plants, mesophyll cells are unequal in shape. They distinguish 2 types of mesophyll: 1) columnar (palisade), adjacent to the upper side of the leaf; 2) spongy (loose), adjacent to the underside of the leaf.
Columnar mesophyll consists of closed cells, elongated in length perpendicular to the surface of the leaf. This tissue receives more light and contains a maximum number of chloroplasts. 80% of photosynthesis takes place here.
The shape of the cells is not random:
1) Thanks to this shape, chloroplasts are protected from very bright sunlight. With a sharp increase in the intensity of illumination, chloroplasts from short walls go to long, perpendicular to the surface of the leaf.
2) It is necessary that the organic substances formed in the cells of the leaf are quickly removed. With this form of cells, the outflow of assimilating substances proceeds quite quickly.
spongy mesophyll- loose tissue, with a large number of intercellular spaces. The cells are usually rounded and there are much fewer chloroplasts in them. Less light gets to them and only 20% of photosynthesis takes place in spongy tissue cells. Nevertheless, the value of this fabric is very great, precisely due to the developed system of intercellular spaces, which contribute to 1) transpiration, because in the intercellular spaces, water vapor is released from the surrounding cells; 2) gas exchange(CO 2 entering through the stomata through the intercellular spaces quickly spreads through the leaf, the released oxygen spreads through the intercellular spaces and exits through the stomata ( vice versa when breathing)) the normal course of photosynthesis.
If the leaf is facing the light with its edge, then the columnar tissue develops on both sides of the leaf.
The distribution of spongy and columnar tissue depends on the illumination. The greater the illumination, the more developed the columnar tissue. With shading, spongy tissue develops more strongly and transpiration will proceed more strongly.
Therefore, the upper (outer) leaves ( light) and lower (located deep in the crown of the tree) ( shadow) have a different ratio of columnar and spongy tissue.
light the leaves are small and thicker, with a powerful cuticle, columnar tissue is well developed.
Shadow the leaves are thinner and larger, the columnar tissue is poorly developed, often 1 layer, the cells are funnel-shaped, directed with the wide side towards the leaf surface, spongy tissue predominates.
In most monocotyledonous plants, some dicotyledons and conifers, the mesophyll is homogeneous, not differentiated into columnar and spongy. This mesophyll is called isopalisade.
3. Conductive and mechanical fabrics - form leaf veins.
The veins are collateral, closed vascular-fibrous bundles. Phloem in a bundle facing bottom side of the sheet, and xylem - To top. From below and from above they are reinforced with sclerenchyma fibers. The veins of the castings branch, and the smaller veins have a simpler structure. They lack mechanical tissues (there are only sieve tubes and vessels). In some plants, thin veins consist only of tracheids, which are in direct contact with leaf tissues. In addition to the transport of water, these tracheids move substances - assimilates. In other plants, thin veins may consist only of sieve elements, tubes have indistinctly expressed "strainers" or they are absent at all, companion cells may disappear, and sometimes become larger. In the terminal sections, such veins are represented only by mother cells of the phloem, not differentiated into sieve tubes and companion cells. Modern research has revealed several types of structure of small veins (see textbook.)
Many plants have a lining of parenchymal cells around the veins. These cells are elongated along the veins and do not contain chloroplasts. Through them, the products of photosynthesis enter the veins.
Sometimes the mechanical tissues of the veins are not enough, and then additional mechanical fabrics. In large veins, collenchyma is added above and below (it is often present in leaf petioles), sometimes additional sclerenchyma develops. The mesophyll can be strengthened by sclereids - idioblasts scattered between assimilation tissues. In some plants, a lot of bast fibers develop in the leaf blade (agave, palm trees, banana, traveler's tree).
4. excretory tissues - glands with essential oils, receptacles of resins, milkers, hydathodes, etc.
Anatomical structure of a coniferous leaf.
Conifers arose in the Late Carboniferous (about 290 million years ago), when the climate on the planet began to dry out. The leaves of modern conifers have many features that indicate their drought tolerance, i.e. possess xeromorphic features. This may be due to the fact that most representatives of this class were finally formed during the dry and relatively cool Permian period (286–248 million years ago). At that time, the gradual increase in aridity probably favored this kind of structural adaptation.
The leaves of conifers are needle-shaped (pine, spruce, fir, larch) or scaly (thuja, cypress), as a rule, evergreen ( excl. Larch - secondary adaptation to very cold climates), are adapted to economical transpiration of water and to endure drought, including winter, when low temperatures roots cannot absorb water.
1) The outer surface of the needles is very small (the evaporation area is small).
2) The epidermis consists of thick-walled cells to a powerful cuticle (protection against evaporation).
3) Submerged stomata. Guard cells are partially lignified, and the channel is filled with resins or wax (a sharp decrease in transpiration).
4) Under the epidermis, there is a special hypodermis tissue, consisting of lignified fibers, which reduces evaporation and increases mechanical strength.
5) The main difference from angiosperms: there is no differentiation into columnar and spongy mesophyll, all cells are homogeneous, form folded mesophyll. This is an adaptive compensation for a small outer surface. In mesophyll cells, the membrane forms internal folds, which ensures a sharp increase in the wall layer of the cytoplasm and the inner surface.
In cells, due to an increase in their inner surface, the number of chloroplasts increases, and with a small outer surface of the needles, photosynthesis processes proceed as intensively as in ordinary leaves of flowering plants.
6) The double vascular fibrous bundle is surrounded by the endoderm, which regulates the transport of substances. When entering the stem, the double bundle merges into one, forming one leaf trail.
7) Conductive bundles are surrounded by transfusion tissue, which consists of: a) radial tracheids (water transport), b) living parenchyma cells (organic assimilating substances transport).
8) There are resin passages located between mesophyll cells.
Leaf metamorphosis.
A leaf can perform functions that are not characteristic of it:
1) The role of the root (salvinia - in the form of thin threads in water - similar organs)
2) Leaves often turn into thorns (in plants of deserts, steppes, savannahs). The mesophyll of the leaf is reduced, and usually only the central vein remains, which is additionally reinforced with sclereids (cacti, barberry, etc.).
Spines are an adaptation for: a) a decrease in the evaporating surface in conditions of water deficiency; b) protection from being eaten by animals.
With the help of an electron microscope, it was possible to find out the role of cactus spines. These are microscopic pumps that draw in air and condense water.
3) The transformation of leaves into tendrils (bean, pumpkin) - serve to support the stem and its attachment.
4) Sometimes the petiole may change. It flattens, becomes green and performs the function of photosynthesis. The leaf blade is often reduced in this case. Characteristic for plants of dry areas (for example, Australian phyllodes acacias)
5) Storage leaves - most often water (aloe, agave, etc.).
6) In insectivorous plants, the leaves turn into trapping devices. They usually have digestive glands that secrete digestive juice.
For the first time these plants were studied by Ch. Darwin. He explained the appearance of these plants. They live where there is little nitrogen, phosphorus and other minerals in the soil (for example, in peat bogs, in tropical rainforests, standing waters). They get the substances they need by digesting insects, sometimes other small animals.
About 500 species of insectivorous plants (predator plants) are known. They are found from the Arctic to the tropics. There are 3 groups of insectivorous plants, differing in the types of traps. These are: 1) traps(sarracenia, nepenthes); 2) Velcro(rosyanka, rosolista, etc.); 3) traps(Venus flytrap, pemphigus).
1. traps . At sarracenia(North America) hunting leaves resemble pitcher flowers. They are brightly colored and have a landing area for insects on the outside, and nectaries at the entrance to the jug. There are also sharp hairs directed downwards, which allow the victim to easily slide down, but do not allow them to rise up. The pitcher is 2/3 filled with liquid. The walls of the jug have digestive glands that secrete digestive juice. More primitive doves are filled with rain oxen, insects that have got there first decompose and then are absorbed by the plant.
Nepenthes(trop. Asia) - a very narrowly specialized liana. The petiole of the leaf consists of 3 parts: the phyllodia, the petiole itself and the brightly colored jug, the colored leaf blade covers the jug. The jug can hold up to 1 liter of liquid containing digestive juice. There are nectaries to attract insects, the walls of the jug are covered with wax and downward hairs. Once in a trap, the insect is digested in 5-8 hours.
2. Velcro. In sundew, the leaves are covered with glandular hairs that secrete a sticky secret. There are also digestive glands. Liquid droplets glisten in the sun like dew drops, attracting prey. No nectar, no smell. Insects sit on the leaf and stick to it, the leaf rolls up and releases digestive juice. The digested food is absorbed. After a few days, the leaf unfolds.
3. traps . The most difficult in the Venus flytrap (North America). The leaf is divided into two parts, the upper one is a trap, sensitive and glandular hairs are located on it. As soon as the insects touch the hairs, the leaf instantly collapses (turgor!).
A difficult trap for pemphigus. (Kr. Book St. region - 3 types). On thin, dissected leaves floating near the surface of the water, there are numerous trapping bubbles (up to 2 mm in diameter). The trapping vesicle has a round opening with a valve and sensitive hairs. There is a negative pressure in the cavity of the bubble, since all the liquid is pumped out of it. Small crustaceans (daphnia, cyclops), ciliates, passing by, touch sensitive hairs, the valve instantly opens and the prey is sucked into the bubble along with water. The valve closes.
We will analyze the structure of the trunk of coniferous trees on a cross section of a pine trunk.
At an early age, the trunk is covered on the outside with a periderm, consisting of a multilayer cork, cork cambium (phellogen) and two to three layers of phelloderm. All these parts of the periderm are difficult to distinguish here and look like one layer. Later, the periderm is replaced by a crust. Under the integumentary tissue is a green parenchyma, or primary cortex (living storage, and in the presence of chloroplasts, assimilation tissue), from loosely located rounded cells. Among them, large vertical (longitudinal) resin passages are visible, the canal of which looks like an oval hole lined with living epithelial cells. Later, these resin passages are cut off with a cork and discarded together with the primary bark, so that they do not matter for the extraction of resin (tap).
From the inside, the bast (secondary bark) adjoins the primary bark. Pine bast consists of sieve tubes, bast parenchyma, and medullary rays (Fig. 13c). As you know, the downward flow of organic substances from the leaves moves along the sieve tubes. Sieve tubes look like small (in Fig. 13, h, they are greatly enlarged) oval cells arranged in radial rows, each of which was formed from one cambial cell. Chains of darker rounded cells stretch across the rows of sieve tubes. These are living cells of the storage bast parenchyma containing starch and other organic substances (fats, proteins), and some cells are crystals of calcium oxalate (drusen), which are waste (see Fig. 14).
Fig.13.
a - periderm; 6 - green parenchyma, primary cortex (1 - resin passages; 2 - parenchyma of the primary cortex); c - secondary bark, bast, phloem (3 - sieve tubes; 4 - bast parenchyma; 5 - core ray; 6 - cambium); d - secondary wood, xylem (7 - late (autumn) tracheids; 8-resin passages; 9 - early (spring) tracheids; 10 - primary core ray; 11 - secondary core ray; 12 - primary wood; 13 - core; 14 - annual ring)
Rice. 14. Scheme of the structure of the chloroplast under an electron microscope (a): 1 - stroma; 2 - grains; 3 - lamellae. Metabolic products in the cell (b):
1 - simple starch potato grains (on the left - concentric, on the right - eccentric); 2 - complex starch grain of oats; 3 - crystals; -4 - intergrowths of crystals (druze). Scheme of the gradual formation of vacuoles in a growing cell (c): 1 - cell membrane; 2 - a narrow layer of the cytoplasm, adjacent to the inside of the shell; 3 - vacuole with cell sap; 4 -- core
In the radial direction, core rays pass along the bast, continuing in the wood. They are chains of living parenchymal cells, wider in the bast and narrower in the wood. The core rays are the most permanent living part of all trees and shrubs. In woody plants, they represent such an important characteristic element of the anatomical structure that they serve as the main diagnostic feature in the anatomical determination of the wood of various trees and shrubs by a key. The core rays arise from the parenchymal cells of the cambium. Through the cells of the core rays, water and organic substances move in the radial direction (across the growth rings). Part of the organic matter can be stored in the cells of the rays in the form of reserves of starch and oils. On a transverse section, the medullary rays are visible as lines or stripes crossing the growth rings, on a radial one - as lighter wide strips (ribbons) running across the fibers, on a tangential section or on the surface of the trunk with the bark removed, they are visible as darker stripes with pointed ends (strokes) running in the same direction as the wood fibers (Fig. 15).
Rice. 15. Scheme of three sections of the trunk (part of the bark is removed and the tangential surface of the tree-3 is exposed - transverse on top, radial on the side): 1 - crust; 2 - bast; 3 -- wide core beam; 4 - annual ring of wood; 5 - cambium; 6 -- core
It can be seen under a microscope that, in a radial section, the medullary rays consist of cells elongated along the ray, and therefore across the wood fibers (Fig. 16, A). On the transverse section, the rays are rows of elongated narrow cells running in the radial direction. On the tangential section, the rays are cut across and look like groups of spindle-shaped small parenchymal cells located between the wood fibers (Fig. 16, B). The rays are strips or ribbons, therefore, they distinguish in the transverse section the length (in the radial direction), width (in the tangential direction) and height (in the radial section in the direction of the fibers). The shorter the beam, the later it was formed from the cambium, and the longer, the earlier. Rays from the core through the entire wood to the bark are called primary core rays. Rays that do not start from the core, but in subsequent annual rings of wood, are called secondary. Rays always begin from the cambium, since once formed a ray does not disappear. The medullary rays have two varieties: narrow, visible in the transverse section as consisting of one row of cells, and wide, consisting of several rows. The beams of wood continue in the bast, where they noticeably expand (see Fig. 13).
Rice. 16. Pine wood in the section (A - radial; B - tangential): 1 - early "e (spring) tracheids; 2 - bordered pores; 3 - late (autumn) tracheids; 4 - core ray (a - - dead tracheid cells with small bordered pores; b - living cells of the ray with simple pores); 5 - walls of the tracheid; 6 - bordered pore; 7 - core ray; 8 - transverse (horizontal) resin passage in a wide core ray; 9 - tracheid cavity; 10 - longitudinal (vertical) resin passage
The cells of the medullary ray are loosely connected. Inside the beam there are always intercellular spaces through which air exchange occurs through the lenticels of the cortex. This is the only way for the barrel to communicate with the atmosphere.
On the border between the bast and wood there is a secondary educational tissue - the cambium, which is a chain of elongated living cells that form secondary wood inward and secondary bark (bast) outward. Inside the cambium lies secondary wood, consisting of 90--95% of spring, summer and autumn tracheids, which together form growth rings (layers). The inner part of the annual layer - early or spring wood - contains tracheids, almost square in cross section, with thin shells. Early tracheids have a wide cavity, their radial walls bear bordered pores for communication with each other in a tangential direction, parallel to the direction of growth rings. This is the main conductive element of the ascending current.
The outer part of the annual layer - late wood - has a slightly brownish color and also consists of tracheids. While remaining the same in width, the tracheids significantly decrease in radius. Their walls are strongly thickened, the cavity is much reduced, there are few bordered pores and they are poorly developed. Late tracheids perform mainly a mechanical function, giving strength to the tree trunk.
Annual rings are crossed across by narrow strips, going, like spokes of a wheel, to the core, which is why they are called core rays. In pine wood, especially in the late part of the annual layers, longitudinal, or vertical, resin passages are visible. They have the same structure as in the primary cortex, that is, they consist of three layers: the inner layer of the lining, or excretory, cells, which forms the epithelium of the resin duct; middle layer of dead cells; the outer layer of cells of the living accompanying parenchyma. The resin passages in the wood are smaller than in the primary bark, but they function during almost the entire life of the tree and are important in the extraction of resin (pumping) of coniferous trees.
In addition to the longitudinal ones, there are transverse, or horizontal, resin passages. They are located in wide medullary rays and are interconnected with vertical resin ducts. In the center of the pine branch lies the core, which looks like a circle with irregular ray outgrowths, turning into primary core rays. Small-celled areas of primary wood (xylem) that arose from the procambium protrude into the space between the rays. In a young pine branch, the core cells are alive, they contain starch.
On a longitudinal (radial) cut, pine wood looks different (Fig. 16, A). Early (spring) tracheids look like long fibers with pointed ends. They bear numerous bordered pores in the form of two concentric circles, located mainly closer to the ends of the tracheids; there are fewer of them in the middle. Late (autumn) tracheids are much narrower than spring ones, have few bordered pores, which, moreover, are much smaller and have only an outer circle, while an oblique fissure replaces the inner one.
The core rays on the radial cut look like ribbons crossing the tracheids in the transverse direction. They consist of cells of two genera: marginal dead cells, bearing small bordered pores and having thickenings in the form of notches, and medium-living cells, having simple pores in the form of light spots. Dead cells serve to conduct water in a horizontal direction - across the growth rings. Living things store reserves of organic substances (carbohydrates, fats, etc.). On a tangential section of pine wood (perpendicular to the radius, Fig. 15, B), core rays (cut across) are visible in the form of spindle-shaped groups of cells. Inside the wide core rays, transverse, or horizontal, resin passages are visible. They, like the vertical ones, are surrounded by an epithelium of thin-walled living parenchymal cells and reinforced by a sheath made of a layer of dead mechanical tracheid cells. Horizontal (transverse) resin ducts, intersecting with vertical (longitudinal) resin ducts, form a dense network called the resinous tree system. It permeates all the wood of the trunk, branches and roots.
The combination of vertical and horizontal resin passages allows resin to flow from the farthest unopened resin passages due to their connection with exposed ones. This is very important for extracting resin by tapping. In the secondary bark (bast) there are only transverse resin passages, which are a continuation of the radial (transverse) passages of wood, since the cambium layer does not interrupt them. Therefore, if you open the resin passage in the bast, resin can flow out of the wood.
The tracheids on the tengental section are dissected along the cavity, and therefore the early (spring) and late (autumn) ones are very difficult to distinguish and look approximately the same. Bordered pores look like thickenings protruding in two adjacent tracheids. Sometimes a vertical, or longitudinal, resin passage enters the field of view of the microscope. It has the same structure on the radial and tangential sections - it is a hollow channel lined from the inside with epithelial cells.
N. ZAMYATINA. Photo by N. Zamyatina and N. Mologina.
Conifers are one of the oldest plants that inhabit our planet. Their geological history is about 370 million years. In the process of such a long evolution, the leaves, or needles, of conifers have retained structural features down to the details of the anatomical structure. They are not as diverse as the leaves of flowering plants, however, they vary in shape, color and size, and some are completely different from the needles we are used to.
Science and life // Illustrations
In most conifers, the tops of the shoots are protected by dense, thin scales that form a bud at the end of the growing season. The kidney scales are covered with a protective layer of resin. In the photo: a young needle breaking out of a bud (10 times magnification).
Norway spruce needles appearing on a young branch (see photo above right). Pillows are visible - protrusions of the cortex, to which needles are attached, and conductive fibrous bundles in the form of grooves (10 times magnification).
The shortest needles (only 1-1.5 cm) are found in Canadian spruce (Picea canadensis).
The five-needle pines include one of the most beautiful pines - the Weymouth pine (Pinus strobus). The needles are bluish-green, soft, thin, up to 10 cm long.
Banks pine (Pinus banksiana).<...>
Atlas cedar needles (Cedrus atlantica).<...>
The needles of larch are soft, flat. On shortened shoots, it is collected in bunches of 20 or more needles in each.
One of the most beautiful firs is Serbian spruce (Picea omorica): the needles are flat, curved, dark green above, shiny, below, thanks to bluish-white stripes, silvery. Small cones of this spruce attract crossbills in winter.
Balsam fir (Abies balsamea).<...>
According to the structure of the needles, pseudo-hemlock is similar to spruce, but differs sharply from it and other coniferous cones in shape, which have funny outgrowths - "tails" on the scales.
Yew berry, or common (Taxus bassata).<...>
Anatomical structure of the Scotch pine needle.
Larch needles appear in early May and fly around at the end of September. In autumn, the tree turns golden yellow.
This is how the surface of a spruce needle looks like when magnified 10 times. The rows of stomata are clearly visible in the photo. Spruce, like all higher plants, breathes and releases oxygen through stomata.
Scotch pine needles (10 times magnification). The serrated edge and rows of stomata located under the endodermis are visible.
A bunch of needles on a shortened larch shoot (10 times magnification).
On the underside of the needles of fir, at high magnification (20 times), two white stripes are visible, in which stomata are located. The tip of the needle is forked.
On the underside of the hemlock needles (10 times magnification), narrow white stomatal stripes and resin secretions are visible.
The upper side of the hemlock needles is shiny, dark green, with longitudinal grooves.
The most common coniferous tree is a spruce familiar to us from early childhood. The needles of spruces in the form of single needles grow over the entire surface of the branch. Each needle is usually tetrahedral. The edges are sometimes not very noticeable, the needles seem almost flat, but you can always see that they are pointed at the end. It turns out that a thick spruce needle, as it were, ends with another very thin needle.
In cross section, the needle forms an irregular rhombus, always directed downward with the largest angle. In this corner is the midrib of the leaf. This design gives the needles rigidity - remember how strong and prickly they are. Immediately below the outer layer of needle cells - the epidermis - there are two layers of cells with very hard shells, giving the needles even greater strength.
Like other conifers, spruce needle leaves have a waxy sheath - a cuticle. It is in these plants that the cuticle is the thickest. Canadian spruce species are distinguished by a special cuticle thickness, the needles of which have a bluish tint. The products of combustion of automobile fuel emitted into the atmosphere are dissolved in the wax shell, which is why conifers do not grow well in the city. Spruce is able to increase the thickness of the cuticle, and the worse the environmental situation, the thicker the wax shell and the brighter the Christmas trees. But when a certain limit is reached, the cuticle breaks down, the needles become dirty gray, lose their luster and fall off.
The needles of spruces of different species are very different from one another. Canadian spruce has very short needles - only 1-1.5 cm, besides, its cones smell not of turpentine, like other spruces, but of blackcurrant and are formed even on the lowest branches; they do not exceed 6 cm in length and ripen in the first year.
In another coniferous tree well known to us - pine branches initially grow like spruce, that is, the needles are located singly and along the entire length of the shoot. The following year, shortened shoots form in the axils of the needles, so tiny that we usually do not pay attention to them. Needle leaves on these shoots grow in bunches of 2 to 50 needles each, depending on the species. Pines are even divided into groups according to the number of needles: 2-, 3- and 5-coniferous.
The most numerous are two-coniferous pines. They grow mainly in Europe and Asia. The best-known two-coniferous trees include Scotch pine, which is ubiquitous in Russia, and Banks pine, which is found in Central Europe. The needles of the Banks pine are short, only 2-4 cm. They are very hard and bristle in different directions, which makes the branches seem "disheveled". By the way, the pine holds the record for the length of foliage among conifers: the North American swamp pine has needles up to 45 cm long.
Triconiferous pines almost all come from America. Five-coniferous - are found among both European and American species; they usually have soft, long, thin and almost non-spiny needles.
One of the most beautiful pines, the Weymouth pine, belongs to the five-needle trees. The needles on its thin, long, slightly drooping branches die off quickly, usually remaining only at 10-15 cm tips. In the conditions of central Russia, the soft, tender needles of the Weymouth pine give the tree a lot of trouble. Of the conifers growing in our gardens and parks, it is this tree that crows like the most. Its needles serve as a source of vitamins in winter. As a result, in the spring, after the snow melts, the ground under the Weymouth pines is covered with a thick layer of branches torn off by crows. Moreover, crows rip off these conifers not only in the city, but also in the forest.
Siberian cedar also has five needles, which also belongs to pines and is called Siberian pine. By the way, in the Moscow region, crows willingly pluck both Siberian cedar and Korean cedar pine, which is distinguished by smaller cones.
In real cedars, the needles are also located in bunches at the tops of shortened shoots. There are a lot of needles in the bunch, they are thin, straight and relatively short; in none of the cedar species do they exceed 5 cm, and in the Cypriot cedar they reach only 1-2 cm, which is why all the branches look like plush ribbons.
The same numerous and short needles in larches. Their needles are similar to ordinary leaves, it is soft, thin, flat, appears in early May during "flowering" and flies around at the end of September. Leaf fall allows this tree to grow north of all other large trees.
In winter, many conifers continue to evaporate water through the needles, but when the soil freezes or the roots are damaged, water does not enter them. The trees dry up like linen in the wind and die. Larch sheds its needles for the winter, and winter drying does not threaten it.
Leaf fall saves larches even in the conditions of a big city: the substances harmful to the tree that have accumulated in the needles over the summer are removed in the fall along with the needles, which allows these trees to live where spruce and pines usually die. Unlike pines, in which the needles fly around along with the twig, the short shoots of larches do not fall off, but for several years new bunches of needles are thrown out every year. In winter, they stick out on the tree like warts.
Not quite familiar to us and fir needles. More than 30 species of firs grow around the Pacific Ocean in the American and Asian continents. These are huge, up to 100 m tall, beautiful trees with smooth bark and cones sticking up, falling apart when ripe. Fir in central Russia is not found in nature. Siberian fir grows in the northeast of the European part, in the Urals and in Siberia, forming dark coniferous forests. Norman fir is found in the Caucasus, the rest of the species grow in the Far East.
It is easy to distinguish a fir from a well-known spruce by a single branch. Fir needles are flat and not prickly at all; it forms two well-marked rows on the branch, leaving the upper part free. Most firs on the underside of the needles have two white stripes in which the stomata are located. In balsam fir, these stripes are wide, which makes the needles appear bright white. There is a very beautiful and unusual in appearance fir, which is called so - one-color. Its needles are grayish-green on both sides. Needles are rare and reach 6-7 cm in length. The branches of this fir resemble a rake. After the leaves fall, flat scars remain on them, so the branches themselves are almost smooth.
Fir is perhaps the most fragrant tree among conifers. Fir foot - thin twigs with needles - a valuable raw material for the production of essential oil, which is used in medicine and cosmetics and serves as a raw material for the production of camphor.
There is another coniferous plant, not too familiar to the inhabitants of the middle lane - pseudo-hemlock. Outwardly, it surprisingly looks like a spruce. It differs from spruce, first of all, in the shape of the cones. Pseudo-hemlock cones are formed not at the ends of young twigs, but on the shoots of the previous year and have far protruding cover scales with long "tails". Pseudo-hemlock needles are located throughout the branch, like a spruce.
Very small, up to 1-1.5 cm, the needles of a real hemlock. Beautiful hemlock trees are found in North America, China, Japan, India. The needles of this plant are flat, like those of a fir, the underside of the needles with white stripes, and more often completely white. The tip of the needle is round.
Long (up to 3 cm) narrow leaves-needles with two yellowish-green stripes on the underside and in yew berry. Its leaves live for a very long time, up to 10 years or more, and throughout their life they accumulate a poisonous substance - taxine. The older the needles, the more poisonous it is. Yew seeds also contain taxin, but there are no toxic substances in the ripened fleshy roof of the fruit, and birds, such as blackbirds, readily eat them.
Details for the curious
In conifers, each needle almost completely reproduces the structure of the stem. The outer layer of needle cells, a kind of "bark", is called the epidermis. On top of the needles are covered with a waxy cuticle. The epidermis is followed by the hypodermis, or subcutaneous tissue, thick-walled cells that protect the leaves from damage (in a tree, wood would correspond to the hypodermis). In many conifers, the hypodermis becomes lignified. Needles of spruce, cedar and pine have a "wooden" shell. The Pitsunda pine has especially hard hypodermis: the upper corners of its needles are literally "booked" with mechanical tissue, which allows the very long needles not to bend at all.
Behind the hypodermis is the most important tissue of the needle - the parenchyma, its deep folds are literally stuffed with green balls of chlorophyll - chloroplasts. It is in the parenchyma that photosynthesis takes place. In the parenchyma, there are resin passages (not all conifers have resin passages), their small cells secrete resin. Each resin passage, like a water pipe, is surrounded by thick-walled cells of mechanical tissue. Even closer to the center of the needle are vascular fibrous bundles surrounded by "inner skin" - the mechanical tissue of the endoderm. Through lignified tissue - xylem - conductive water flows from the branch to the end of the needle. On non-lignified tissue - phloem - organic substances move in the opposite direction. The vascular bundle also has its own parenchyma. Sometimes it is green - working for synthesis, but more often - lignified, especially in long needles. In this case, the vascular fibrous bundle serves as a rigid axis that does not allow the needles to bend.
The stomata through which conifers breathe are usually hidden deep under the endodermis, which makes it possible to greatly reduce water consumption for evaporation in winter, and during drought in summer.
Completed by: O.M. Smirnova teacher of biology Municipal educational institution Uren secondary school
1. Consider the external structure of the pine shoot. How are the needles on the shoot? What appearance needles? 2. Consider the external structure of the spruce shoot. How are the needles on the shoot? What is the difference between the appearance of spruce needles and pine needles? 3. Examine the micropreparation "Pine needles" under a microscope at first magnification of 56, and then 300 times. On the cross section of the needles, find a dense skin covering the needles from the outside, and 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 photophilous. Therefore, its lower branches die off quite early. Under the canopy of other trees, it cannot grow and renew itself. Needle-shaped pine leaves - needles - reach 3-4 cm in length. The needles are arranged in pairs on strongly shortened shoots. For the winter, a pine tree, like most coniferous trees, does not fall off the needles, but stays on the plant for 2-3 years. Needles fall along with shortened stems. The needles are covered with thick skin. There are few stomata, they are arranged in rows and are in depressions. There are only two vascular bundles in the leaf, and they do not have lateral branches. Due to these features, pine economically evaporates moisture and easily tolerates drought. The leaves also ate needles, but they are much shorter and more prickly.
