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Introduction

Almost the only source of energy for all living organisms is the energy of the sun. Only one group of organisms can directly convert solar energy - green plants and photosynthetic organisms. We are talking about a unique natural phenomenon - photosynthesis. All other organisms absorb the energy of the sun, converted by green plants into the energy of organic substances - sugars. The main plant organ involved in photosynthesis is the leaf. Therefore, the study of plant leaves is very actual topic. Plants themselves use the produced substances as a source of nutrition. It would seem that the larger the leaf, the better, since more “food” is produced. But in the vast majority of our northern plants of forests and meadows, the leaves are medium-sized and even small. So what does the shape of the leaf depend on? We assumed hypothesis- the form depends on environmental conditions - illumination, temperature, humidity.

This question determined goal our research - find out the relationship between environmental conditions and the shape of the leaf blades of meadow and forest plants

Tasks:

Consider the features of the internal, external structure of the leaf, as the main organ of plants, its functions;

Determine how the influence of environmental conditions on the shape of the leaf blade is manifested;

Collect samples of light-loving meadow plants and shade-loving forest plants;

Conduct a study - compare the sizes, shapes of leaf blades of light-loving and shade-loving plants

An object research: green plants

Subject research: leaf blades of plants in our area.

Chapter 1

1.1. External leaf structure

The external structure of the leaf. The leaf always occupies a lateral position in the shoot, located at the nodes of the stem. In the predominant number of higher plants, the leaf has a flat shape.

A leaf is distinguished by a leaf blade, petiole, stipules and a base with which it is attached to the stem. There are plants in which the petiole and stipules are absent. Many plants have simple leaves - they have only one leaf blade (Figure 1).

Rice. one. The external structure of the sheet: 1 - leaf blade; 2 - veins; 3 - petiole; 4 - stipules; 5 - base of the sheet

There are plants in which the leaf has several leaf blades. Such leaves are called complex (Figure 2).

Rice. 2. Variety of leaves. simple leaves: 1 - lilac; 2 - Apple tree; 3 - maple; 5 - dandelion. compound leaves: 4 - clover; 6 - rose hip; 7 - raspberry; 8 - strawberry; 9 - lupine

When studying the external structure of the leaf, it is clearly seen that the veins are clearly expressed on the leaf blade of many plants. They are represented by bundles of conductive and mechanical tissue. Through the veins, water and mineral salts enter the leaf and the organic substances formed in the leaf are discharged. In some plants, the veins are approximately the same in size and lie arcuately or parallel to each other. In others, they are represented by a pinnately branched network of small veins converging into one large central vein in the middle of the leaf. Pinnate and palmate venation is characteristic of the leaves of dicotyledonous plants, while parallel and arcuate venation is characteristic of the leaves of many monocotyledonous plants (see Appendix 1, c).

Plants have different sizes of leaves. So, in palm trees, monstera, white water lilies and yellow water pods, the leaves are very large: their length, together with the petiole, reaches 150-200 cm, in some palms even 5-12 m. But in heather and needles, they are very small, only 2 long -3 mm..

1.2. The internal structure of the leaf

Outside, the leaf is covered with skin. It is formed by a layer of transparent cells of the integumentary tissue, tightly adjacent to each other. The peel protects the inner tissues of the leaf. The walls of its cells are transparent, which allows light to easily penetrate into the leaf.

On the lower surface of the leaf, among the transparent cells of the skin, there are very small paired green cells, between which there is a gap. A pair of guard cells and a stomatal gap between them is called a stomata. With insufficient water supply, the stomata of the plant are closed. With the flow of water into the plant, they open (Figure 3).

Rice. 3. Participation of stomata in gas exchange and moisture evaporation

Stomata are found in the skin of all land plants. Their number in plants is huge - from 80 to 300 pieces and more per 1 mm² of leaf surface. For example, maple has 550 stomata per 1 mm2 of leaf surface, and yellow pods have 650.

Leaf tissue. Inside the leaf there are a lot of cells of chlorophyll tissue - the pulp of the leaf. Due to the large number of chloroplasts in the pulp cells, the leaf has a green color. The presence of a large number of green chloroplasts in the pulp of the leaf indicates that photosynthesis is carried out in this part, that is, organic substances are formed here.

Two types of cells are distinguished in the pulp of leaves. According to the appearance of the cells and their location in the pulp of the leaf, columnar and spongy tissues are distinguished. Columnar tissue cells contain most (about ¾) of all leaf chloroplasts. They are better lit, they form the most organic substances in the light. Through the loose spongy tissue, gas exchange and water evaporation occur (Fig. 4).

The structure of the leaf pulp is presented differently in leaves developing under different lighting conditions. In plants grown in bright light conditions, the leaves usually have two or three layers of columnar tissue - they are called light. In plants grown with a lack of light, in the shade, columnar cells form only one thin layer in the upper part of the leaf - they are called shadow cells.

Rice. four. Scheme of the internal structure of the leaf

In most plants, stomata are located mainly on the underside of the leaf, but in some (for example, eucalyptus, cabbage) they are on both sides of the leaf. In plants with leaves floating on water (pod, water lily), stomata formed only on the upper side of the leaf, facing the air.

1.3. Sheet functions

Formation of organic substances. A green leaf performs an important function in the life of a plant - organic substances are formed here. The structure of the leaf is well suited to this function: it has a flat leaf plate, and the pulp of the leaf contains a huge amount of chloroplasts with green chlorophyll.

The formation of organic substances in the process of photosynthesis is one of the main functions of the leaf.

Evaporation of water is another important function of the leaf. Evaporation provides the relationship between the roots and leaves of the plant.

The process of evaporation of water by the leaves of a plant is regulated by the opening and closing of stomata. By closing the stomata, the plant protects itself from water loss.

Of the external factors, the work of stomata is affected by dry air, water supply conditions, light brightness and temperature. So, during a drought, most plants have stomata closed. Many plants open their stomata only in the evening and at night when the heat subsides. But in most trees, shade-tolerant plants, and many grasses, the maximum evaporation of water occurs in the daytime.

Gas exchange. Leaves, thanks to the work of stomata, also carry out such an important function as gas exchange between the plant and the atmosphere. Through the stomata, oxygen and carbon dioxide enter the leaf with atmospheric air.

Leaf fall. In the process of life, the leaves age by the end of the growing season, nutrients flow out of them, chlorophyll begins to break down, the leaves turn yellow or reddish, and waste waste substances accumulate in the leaf tissues. Aged leaves are removed due to leaf fall. This adaptation, developed in the process of evolution, provides not only the removal of substances unnecessary for the plant, but also a reduction in the surface of above-ground organs during an unfavorable period of the year.

In some plants, the leaves have acquired other functions. Many plants reproduce by leaves (vegetative propagation). Some plants store spare nutrients in their leaves, such as sedum, juvenile, aloe, cabbage, onion.

Common peas and mouse peas, along with ordinary leaves, have leaves in the form of antennae. With their help, the non-erect shoots of these plants, clinging to a support, rise higher and are carried out to the light.

In barberry, caragana, camel thorn, some leaves have become thorns that protect the shoots from animals. In cacti, the leaves have changed into sharp needles.

In nature, there are many plants that are able to catch insects with the help of leaves and digest them. Typically, such insectivorous plants grow on soils poor in minerals, especially with insufficient nitrogen, phosphorus, potassium and sulfur. From the bodies of insects, these plants receive the inorganic substances they need.

In lakes in Russia, a pemphigus plant is often found floating near the surface of the water. Among its threadlike green leaves, some are shaped like trapping bubbles (2-5 mm in diameter) with a cap. Small animals caught in them, such as daphnia, are digested and absorbed by the plant. So the plant compensates for the deficiency of minerals (especially nitrogen compounds), which are not enough in lake water.

Chapter 2

2.1. The influence of climatic characteristics on the sheet size

The modern distribution of plants on Earth is believed to be determined by climate, and thus vegetation zones almost always correspond to climatic zones. Climate and soils primarily affect the external characteristics of vegetation species, which determines the external similarity of plants from areas with similar ecological conditions. Leaves, as photosynthetic organs of a plant, are optimally adapted to climatic conditions.

The shape of the leaf blade reflects the characteristics of the environment.

This assumption was confirmed by the results of research by scientists from the universities of Tübingen (Germany) and Lyon (France), who studied the dependence of the shape of the leaf blade of European trees on climatic factors. Scientists limited themselves to the study of woody vegetation. The material was collected on the territory of Europe, data were obtained on 1835 plots. At each site, tree species were grouped according to 25 indicators.

Result: leaf shape mainly depends on temperatures (average annual, total, minimum, duration of soil freezing), and to a greater extent on the minimum than on the maximum - the closest relationship is observed between the minimum temperature and the presence of a sharp base in the leaves. The relationship between the presence of entire leaves in trees and temperature is somewhat weaker, although cold can be considered as a stress factor that contributes to the formation of irregularities along the edge of the leaf blade. Precipitation-related parameters did not have a significant relationship with leaf shape parameters.

The data obtained indicate that adaptation to cold, mainly to the lowest temperatures, was of paramount importance in the evolution of deciduous flora.

2.2. The dependence of the shape of the leaf blade on the illumination

2.2.1. The influence of light on the structure of leaves

The anatomical structure of the leaves of light-loving and shade-loving plants presents important differences. The leaves of light-loving plants are often equilateral if they occupy a vertical position, while the leaves of shade-loving plants are always bilateral.

Light-loving and shade-loving (heliophilic and heliophobic) plants differ significantly from each other both in their external form and in their internal structure.

Strong lighting slows down the growth of shoots; therefore, heliophilic plants are often short-segmented and compressed, while heliophobic plants, on the contrary, are long-segmented.

The plants that make up the forest carpet are usually tall, with a long stem. The leaves of light-loving plants are usually narrow, shallow, linear or similar in shape, while shade-loving plants in the same conditions have large, broad leaves. The leaves of a two-leaved mainica, a plant that usually grows in the shade of shrubs, reach only 1/3 of their usual size in the sun.

The leaves of many plant species reach a larger size in northern countries than in more southern latitudes, which, apparently, is associated with a longer period of low light.

The leaves of light-loving plants are often folded (cereals, palm trees), or curly and tuberculate, while the leaves of shade plants are flat and smooth.

The palisade tissue of shade plants is always low (stems, poor in leaves or completely devoid of leaves, usually have a high palisade tissue around the stem); on the other hand, spongy tissue reaches a more powerful development in heliophobic plants. The leaves of typical heliophobic plants consist of only one row of cells (spiky rump). The leaves of heliophilous plants have narrow intercellular spaces, while the leaves of heliophobic plants have wide intercellular spaces.

The skin (epidermis) of light-loving plants is thick and usually does not contain chlorophyll (it is always devoid of chlorophyll on the upper side of the leaf); sometimes it is transformed by transverse cell division into a multilayer aquifer (tropical plants); her cuticle is always thickened.

The skin of shade plants is thin and single-layered, sometimes contains chlorophyll and is covered with a thin cuticle. The leaves of light-loving plants are often shiny and reflect a lot of light, as numerous tropical plants serve as an example.

The leaves of shade plants have a matte color and fade in dry air much faster than the leaves of light-loving plants. The epidermal cells of the leaves of light-loving plants, especially on the upper side of the leaf, have less wavy walls than those of the leaves of shade plants. Only the lower surface of bilateral leaves of light-loving plants is provided with stomata, or at least they are more numerous here than on the upper side (some alpine plants are an exception) and are immersed in the leaf tissue. In shade plants, the stomata are evenly distributed on both sides of the leaf, in any case, but more numerous on the underside, and at the same time lie in the same plane with the entire surface of the leaf, or even elevated above it.

The degree of hairiness is very different. Heliophilous plants, often covered with dense hairs, gray-felt or silvery-white in color, have a slight pubescence, especially on the lower surface (many plants growing on rocks, on heaths and in the steppes). The leaves of heliophobic plants are generally much less hairy, sometimes even completely bare.

With regard to the effect of light on the color of plants, it should be noted that in addition to the importance of light for the formation of chlorophyll, it can also, apparently, cause the formation of red cell sap (antokiana). Under the influence of direct sunlight, the epidermal cells of the bare parts of plants are often stained red, which apparently serves as a protection for protoplasm and chlorophyll (many young shoots, seedlings, alpine and other plants), although there are assertions that the color of the latter may depend on from the influence of the cold.

In addition, a number of researchers point out that the color of leaves, flowers and fruits of plants at higher latitudes is more intense, which may be due to the effect of almost continuous illumination.

From what has been said above, it is obvious that light has a great influence on the external form and internal structure of plants. This is also confirmed by the ability of many plants to adapt their anatomical structure and, mainly, the structure of their leaves to different lighting conditions ("plastic leaves"). A beech leaf, for example, has a different structure in the sun than a leaf of the same beech tree in the shade. The location of chlorophyll grains in the cell and the color of the leaves associated with this depend on the lighting, stronger lighting causes a less intense color, and vice versa.

2.2.2. Classification of plants in relation to light

In relation to light, all plants, including forest trees, are divided into the following ecological groups:

heliophytes (light-loving), requiring a lot of light and able to tolerate only slight shading (photophilous include almost all cacti and other succulents, many representatives of tropical origin, some subtropical shrubs);

sciophytes (shade-loving) - on the contrary, they are content with insignificant lighting and can exist in the shade (various conifers, many ferns, some decorative leafy plants belong to shade-tolerant ones);

shade-tolerant (facultative heliophytes).

Heliophytes. light plants. Inhabitants of open habitats: meadows, steppes, upper tiers of forests, early spring plants, many cultivated plants.

Small size of leaves seasonal dimorphism occurs: leaves are small in spring, larger in summer;

Leaves are located at a large angle, sometimes almost vertically;

leaf blade shiny or densely pubescent;

form scattered stands.

Sciophytes. Can't stand strong light. Habitat: lower darkened layers; inhabitants of the deep layers of water bodies. First of all, these are plants growing under the forest canopy (oxalis, hoof, goatweed).

They are characterized by the following features:

Leaves are large, tender;

Leaves are dark green

Leaves are mobile

The so-called leaf mosaic is characteristic (that is, a special arrangement of leaves, in which the leaves do not obscure each other as much as possible).

Shade-tolerant. They occupy an intermediate position. They often thrive in normal lighting conditions, but can also tolerate dark conditions. According to their characteristics, they occupy an intermediate position.

Chapter 3

For research, we took herbarium samples of meadow and forest plants that we collected at the end of June.

Study #1.Comparison of the leaf area of ​​meadow heliophytes and shade-tolerant forest plants.

The measurement method was used. From each sample, 10 green leaves are selected by random sampling, the area is determined by the method of linear measurements along the length (L) and maximum width (W). The area of ​​the measured leaves (S) is calculated by the formula:

where n is the number of measured leaves.

This method is suitable for cereals and other crops with linear, round leaves.

forest plant			meadow plant

S (forest plants) = 87.5×45.2×0.7×10=27685mm

S (meadow plants) = 44.1 × 7.4 × 0.7 × 10 = 2284.4 mm

Conclusion: The area of ​​leaf blades of forest plants is more than leaf blades of meadow plants by about 13 times.

The reason is different lighting conditions.

Study #2

Comparison of meadow and forest plants according to the shape of the leaf blade (See Appendix 1, p. 23).

forest plants	Record shape	meadow plants	Record shape
bird cherry	blunt two-serrated edge	Alfalfa hop	trifoliate leaf ciliary edge
Stone berry	odd-pinnate Two-toothed edge	red clover	trifoliate leaf The edge is simple
	odd-pinnate Serrated edge	Meadow fescue	line sheet The edge is simple
	obovate Serrated edge	Bedstraw northern	palm leaf Two-serrated edge
Cotoneaster	Oval The edge is simple	Meadow rye	Needle The edge is simple
	Oval Edge ciliary	field bindweed	Cordate The edge is simple
bracken fern	Complex odd-pinnate The edge is simple	Reed grass	Linear sheet, plain edge
Gircha caraway	Complex odd-pinnate vane leaf	Velcro ordinary	line sheet The edge is simple
Cowberry	Leaf simple obovate	Daisy	line sheet Serrated hay
Voronet spike-shaped	Complex odd-pinnate Bladed edge is two-serrated	River gravel	trifoliate leaf Two-serrated edge

Conclusion: In the forest, shrubs have simple leaves, while most herbs have compound leaves. Apparently, this is due to a small amount of light near the surface of the earth and the need for plants to increase the area of ​​the leaf blade due to complex leaves.

In the meadow - the leaves are linear (in cereals), less often - simple and complex.

Study #3

The study of forest and meadow plants by the color of the leaf blade (visually).

Comparing the leaves of meadow and forest plants, we saw that the leaves of meadow plants have a bright green color (cereals, meadow geranium, field loach, blue cyanosis, grass carnation, gravel and others), some light green, sometimes resembling plaque (gray-green hiccups , wormwood, five-lobed motherwort, silver cinquefoil).

The leaves of forest plants have a bright green and dark green color, almost all (blueberries, cotoneaster, ferns, mountain ash, bird cherry, strawberries, lingonberries and others).

Conclusion- forest plants have darker leaves with more chloroplasts due to the lack of light under the forest canopy.

Conclusion

At the beginning of the work, we set ourselves the goal of finding out the relationship between environmental conditions and the shape of leaf blades of meadow and forest plants. After reviewing the work of other authors on this topic and conducting our own research, we can conclude:

The leaf occupies a lateral position in the shoot; in most higher plants, the leaf has a flat shape. The flat shape of the leaf provides the greatest contact of the plant surface with the air and sunlight.

A leaf is a special organ containing cells that capture the sunlight necessary for photosynthesis (air nutrition). In addition, the leaf is involved in gas exchange and transpiration - the evaporation of moisture.

Leaves, as photosynthetic organs of a plant, are optimally adapted to climatic conditions. The shape of the leaf mainly depends on temperatures, and to a greater extent from low temperatures than from high ones. There is a relationship between the presence of entire leaves in trees and temperature. Precipitation does not affect the shape of the leaf blade (in the temperate zone).

Light has the greatest influence on the external shape and internal structure of plants. The location of chlorophyll grains in the cell and the color of the leaves associated with this depend on the lighting, stronger lighting causes a less intense color, and vice versa.

We conducted research comparing meadow and forest plants, and came to the conclusion that the leaves of meadow plants have a smaller leaf blade area, lighter in color, the leaves are mostly simple than those of forest plants. They identified the reason - a different level of illumination. Light is the main factor affecting plants.

We consider our hypothesis - the shape of the leaves depends on environmental conditions - light, temperature, moisture, to be confirmed.

Information sources

Biology textbook grade 6. Electronic version (http://blgy.ru/biology6/leaf)

http://agrosbornik.ru/innovacii1/106-2011-10-09-15-29-31.html

http://eco-rasteniya.ru/svet-kak-ekologicheskij-faktor.html

http://lektsii.com/1-100601.html

http://botanical_dictionary.academic.ru/5917

https://ru.wikipedia.org/wiki/

dic.academic.ru/dic.nsf/bse/74352/

Attachment 1

The difference between leaves in shape, edge of the leaf blade, venation

Leaf Shape:

Fan-shaped: semi-circular, or in the form of a fan

Bipinnate: Each leaf is pinnate

Deltoid: leaf is triangular, attached to the stem at the base of the triangle

Lateform: Divided into many lobes

Pointed: wedge-shaped with a long apex

Needle: thin and sharp

Cuneiform: the leaf is triangular, the leaf is attached to the stem at the apex

Spear-shaped: sharp, with spines

Lanceolate: the leaf is long, wide in the middle

Linear: the leaf is long and very narrow

Bladed: with multiple blades

Spatulate: spade-shaped leaf

Unpaired: pinnate leaf with apical leaflet

Oblanceolate: upper part is wider than the lower part

Reverse heart-shaped: leaf in the form of a heart, attached to the stem at the protruding end

Obovate: in the form of a tear, the leaf is attached to the stem at the protruding end

Oval: the leaf is oval, with a short end

Oval: leaf is oval, ovoid, with a pointed end at the base

Single-bladed: with one leaf

Rounded: round shape

Palmate: the leaf is divided into finger-shaped lobes

Parapinnate: pinnate leaf without apical leaf

Pinnatisected: a simple dissected leaf in which the segments are arranged symmetrically about the axis of the sheet plate

Pinnate: two rows of leaves

Attachment 1

Reniform: kidney-shaped leaf

Dissected: the leaf blade of such a leaf has cuts reaching more than two-thirds of its half-width; parts of the leaf blade of a dissected leaf are called segments

Rhomboid: diamond-shaped leaf

Crescent: in the form of a sickle

Heart-shaped: in the form of a heart, the leaf is attached to the stem in the region of the dimple

Arrowhead: A leaf shaped like an arrowhead, with flared blades at the base

Three-pinnate: each leaf is in turn divided into three

Trifoliate: the leaf is divided into three leaflets

Subulate: in the form of an awl

Thyroid: leaf rounded, stem attached from below

leaf edge

Full edge - with a smooth edge, without teeth

Ciliated - with fringe around the edges

Toothed - with cloves, like a chestnut. The step of the clove can be large and small.

• Round-toothed - with undulating teeth, like a beech.

  Fine-toothed - with fine teeth

Lobed - rugged, with notches that do not reach the middle, like many oaks

Serrated - with asymmetrical teeth directed forward towards the top of the leaf, like a nettle.

• Two-pronged - each clove has smaller teeth

  Finely serrated - with small asymmetrical teeth

Notched - with deep, wavy cutouts, like many species of sorrel

Spiny - with inelastic, sharp ends, like some hollies and thistles.

The leaf is a very important plant organ. This is the part of the shoot whose main functions are transpiration and photosynthesis. The structural features of the leaf are its high morphological plasticity, great adaptive capabilities and variety of forms. The base can expand in the form of stipules - leaf-shaped oblique formations on each side. In some cases, they are so large that they play a certain role in photosynthesis. Stipules are attached to the petiole or free, they can be shifted to the inside, and then they are called axillary.

External leaf structure

Leaf blades vary in size: they can be from a few millimeters to ten to fifteen meters, and for palm trees - even as much as twenty meters. The structure of the leaf determines the life span of the vegetative organ, it is usually short - no more than a few months, although for some it ranges from one and a half to fifteen years. Shape and size are hereditary traits.

leaf parts

The leaf is a lateral vegetative organ that grows from the stem, has a growth zone at the base and bilateral symmetry. It usually consists of a petiole (with the exception of sessile leaves) and a leaf blade. In a number of families, the leaf structure also suggests the presence of stipules. The external organs of plants can be simple - with one plate, and complex - with several plates.

The leaf cushion (base) is the part that connects the leaf to the stem. The educational tissue located here gives rise to the petiole and leaf blade.

The petiole is a narrowed part, connecting the stem and the leaf blade with its base. It orients the leaf relative to the light, acts as a place where the intercalated educational tissue is located, due to which the growth of the vegetative organ occurs. In addition, the petiole weakens the impact on the leaf during rain, wind, hail.

Leaf blade - usually a flat expanded part that performs the functions of gas exchange, photosynthesis, transpiration, and in some species also the function of vegetative reproduction.

Speaking about the anatomical structure of the leaf, it is necessary to say about the stipules. These are leaf-shaped paired formations at the base of the vegetative organ. When the sheet is unfolded, they may fall off or remain. Designed to protect the axillary lateral kidneys and insert educational tissue.

Compound and simple leaves

The structure of a leaf is considered simple if it has one leaf blade, and complex if there are several or many plates with joints. Due to the latter, the plates of complex leaves do not fall together, but one at a time. But some plants may fall completely.

Whole leaves in shape can be lobed, separate or dissected. In a bladed leaf, cuts along the edge of the plate are up to 1/4 of its width. A separate organ is characterized by a larger depression, its lobes are called lobes. The dissected leaf has cutouts along the edges of the plate, reaching almost to the midrib.

If the plate is elongated, with triangular segments and lobes, the leaf is called plow-shaped (for example, in a dandelion). If the lateral lobes decrease towards the base, are uneven in size, and the final lobe is round and large, a lyre-shaped external organ of the plant is obtained (for example, in a radish).

The structure of a sheet with several plates is significantly different. Allocate palmate, ternary, pinnate organs. If a complex leaf includes three plates, it is called trifoliate, or trifoliate (for example, maple). A leaf is considered palmately complex when its petioles are attached to the main petiole at one point, and the plates diverge radially (for example, lupine). If the lateral plates on the main petiole are present on both sides along the length, the leaf is called pinnate.

Forms of whole plates

In different plants, the forms of leaf blades are not the same in terms of the degree of dissection, outline, type of base and top. They can have round, oval, triangular, elliptical and other outlines. The plate is elongated, and its free end can be blunt, pointed, sharp or pointed. The base is attenuated and narrowed towards the stem, it can be heart-shaped or rounded.

Attachment to the stem

Considering the structure of the leaf of a plant, a few words should be said about how it is attached to the shoot. Attachment is carried out using long or short petioles. There are also sessile leaves. In some plants, their bases grow together with the shoot (downward leaf), and it happens that the shoot pierces through the plate (pierced leaf).

Internal structure. Skin

The epidermis (upper skin) is an integumentary tissue located on the reverse side of a plant organ, often covered with cuticles, hairs, and wax. The internal structure of the leaf is such that on the outside it has a skin that protects it from drying out, mechanical damage, the penetration of pathogens to internal tissues and other adverse effects.

Skin cells are alive, they are different in shape and size: some are transparent, large, colorless, tightly adjacent to each other; others are smaller, with chloroplasts that give them a green color, such cells can change shape and are arranged in pairs.

Stoma

Skin cells can move away from each other, in which case a gap appears between them, which is called stomatal. When the cells are saturated with water, the stomata open, and when the fluid drains, it closes.

The anatomical structure of the leaf is such that air enters the inner cells through the stomatal gaps and gaseous substances come out through them. When plants are not sufficiently provided with water (this happens in hot and dry weather), the stomata close. So representatives of the flora protect themselves from drying out, since with closed stomatal crevices, water vapor does not go outside and is stored in the intercellular spaces. Thus, during the dry period, plants retain water.

Main fabric

The internal structure of the leaf cannot do without columnar tissue, the cells of which are located in the upper side facing the light, tightly adjoin each other, and have a cylindrical shape. All cells have a thin shell, nucleus, chloroplasts, cytoplasm, vacuole.

Another main fabric is spongy. Its cells are round in shape, located loosely, between them there are large intercellular spaces filled with air.

What will be the structure of the leaf of the plant, how many layers of spongy and columnar tissues are formed, depends on the lighting. In leaves grown in the light, the columnar tissue is much more developed than in those that grew in dark conditions.

The leaf is one of the main organs of higher plants, occupying a lateral position on the stem.

It develops from the outer layers of the meristem of the growth cone of the stem in the form of a leaf tubercle. Limited apical growth is characteristic, the duration of the growth period is short. It is a monosymmetrical organ, because. has one plane of symmetry. Life expectancy varies from several months (for herbaceous and deciduous woody plants) to 3-10 years (for conifers). Sizes from 3-10 cm to several tens of meters (for the Brazilian palm - resinous raffia, the length of the leaf blade is 20 m).

The leaf is the outer organ of a plant whose main function is photosynthesis. For this purpose, the leaf typically has a lamellar structure to allow cells containing the specialized pigment chlorophyll in chloroplasts to access sunlight. The leaf is also the organ of respiration, evaporation and guttation (excretion of water droplets) of the plant. Leaves can retain water and nutrients, and some plants perform other functions.

Sheet functions:

photosynthesis (from the Greek csfp - light and wenieuit - synthesis, combination, placement together) - the process of formation of organic matter from carbon dioxide and water in the light with the participation of photosynthetic pigments (chlorophyll in plants, bacteriochlorophyll and bacteriorhodopsin in bacteria). In modern plant physiology, photosynthesis is more often understood as a photoautotrophic function - a set of processes of absorption, transformation and use of the energy of light quanta in various endergonic reactions, including the conversion of carbon dioxide into organic substances.

gas exchange is the main form of dissimilation in humans, animals, plants and many microorganisms. During respiration, substances rich in chemical energy belonging to the body are oxidized to energy-poor end products (carbon dioxide and water), using molecular oxygen for this.

In organisms that have large surface areas in contact with the environment, respiration can occur due to the diffusion of gases directly to the cells through the pores (for example, in plant leaves, in cavitary animals).

transpiration (from lat. trans and lat. spiro - I breathe, I exhale) is the evaporation of water by a plant. Water evaporates from the leaf surface through the cell walls of the epidermal cells and integumentary layers (cuticular transpiration) and through the stomata (stomatal transpiration).

As a result of the loss of water during transpiration, the sucking force in the leaf cells increases. This leads to an increase in the absorption of water from the xylem vessels by the leaf cells and the movement of water along the xylem from the roots to the leaves. Thus, the upper terminal motor involved in the transport of water up the plant is due to leaf transpiration.

The upper end motor can operate when the lower end motor is completely turned off, and for its operation not only metabolic energy is used, as in the root, but also the energy of the external environment - temperature and air movement.

Transpiration saves the plant from overheating. The temperature of a strongly transpiring leaf may be about 7°C lower than that of a non-transpiring wilted leaf. In addition, transpiration is involved in creating a continuous flow of water with dissolved mineral and organic compounds from the root system to the aboveground organs of the plant.

vegetative reproduction - the formation of a new individual from the multicellular part of the body of the parent individual, one of the methods of asexual reproduction characteristic of multicellular organisms.

In higher plants, it occurs either as the disintegration of the maternal individual into two or more daughter individuals (for example, when creeping shoots or rhizomes die off, the separation of root offspring), or as the separation of the rudiments of daughter ones from the maternal individual (for example, tubers, bulbs, brood buds).

In some plants, shoots separated from the mother plant (in willows) or leaves may take root.

protection of the plant (scales, spines, attachment to the support with antennae);

supply of nutrients and water.

Morphological parts of the leaf

The leaf, as a rule, is a flat dorsiventral organ, the shape and dimensions of which contribute to the creation of a maximum photosynthetic surface at optimal transpiration values. The number of leaves on a plant varies greatly. It is believed, for example, that one oak tree bears up to 250,000 leaves. The flat shape makes the leaf bifacial, i.e. bilateral. Therefore, we can talk about the upper and lower sides of the leaf, meaning the orientation of these sides in relation to the top of the shoot. The upper side can also be called the ventral, or adaxial, and the lower, dorsal, or abaxial. This is due to the position of the leaf germ in the kidney. The upper and lower sides often differ significantly in anatomical structure, the nature of venation and color. The size of the leaves most often ranges from 3 to 10 cm, however, giant leaves of some palm trees up to 15 m long are known. The largest leaves of the famous Amazonian water lily Royal Victoria (Victoria regia) reach 2 m in diameter. The size, shape and degree of dissection of the leaves, although they are hereditary features of a particular species, are very variable and also depend on the living conditions of its individuals. An adult leaf is usually divided into a plate or several plates (in compound leaves) and a petiole - its narrow stem-like part connecting the plate and the shoot node. The lowest part of the leaf, articulated with the stem, is called the leaf base. Often, at the base of the leaf, paired lateral outgrowths, stipules, of different sizes and shapes are noticeable (Fig. 1). The lamina is the main part of the leaf, as a rule, performing its main functions. The plate is reduced extremely rarely, and then its functions take on either an extended leaf-shaped petiole - phyllodes (in Australian acacias), or large leaf-shaped stipules (in some types of ranks).

Fig.1. A - petiolate, B - sessile, C - with a small pillow at the base of the petiole, D and D - vaginal, with stipules: free - E, adhering to the petiole - G, axillary accreting - C. 1 - leaf blade, 2 - base of the petiole, 3 - vagina, 4 - stipules, 5 - petiole, 6 - axillary kidney

The petiole is usually rounded or flattened in cross section. In addition to supporting and conducting functions, while retaining the ability to intercalate growth for a long time, it can regulate the position of the plate, bending towards the light. Often the petiole does not develop, and then the leaf is called sessile. A leaf with a petiole is called petiolate.

The base of the leaf takes on a different shape. Quite often it is narrowed or looks like a small thickening (leaf pad). However, often, especially in cereals and umbrella plants, it grows and forms a closed or open tube, called a leaf sheath. The leaf sheath protects the axillary buds, contributes to the long-term preservation of the intercalary meristem of the stem, and often serves as an additional support for the shoot.

A bud may form in the leaf axil (which in this case is called an axillary bud).

In the process of leaf formation, stipules grow before the plate and play a protective role, forming part of the renal integument. After the deployment of the kidneys, the stipules often fall off or dry out. Occasionally, they are comparable in size to the size of the leaf blade (especially in compound leaves, in particular, in pea leaves), and function as photosynthetic organs. In the buckwheat family, stipules, as a result of fusion, form a so-called bell, covering the stem above the node in the form of a short membranous tube.

Not all plants have all of the above parts of the leaves; in some species, paired stipules are not clearly expressed or absent; the petiole may be absent, and the leaf structure may not be lamellar. A huge variety of structure and arrangement of leaves are listed below.

External characteristics of a leaf, such as shape, edges, hairiness, etc., are very important in identifying a plant species, and botanists have developed a rich terminology to describe these characteristics. Unlike other organs of the plant, the leaves are the determining factor, since they grow, form a certain pattern and shape, and then fall off, while the stems and roots continue to grow and change throughout the life of the plant and for this reason are not determining factor.

simple and compound leaves

From the way the leaf blades are divided, two main leaf shapes can be described.

A simple leaf consists of a single leaf blade and one petiole. Although it may be composed of several lobes, the spaces between these lobes do not reach the main leaf vein. A simple leaf always falls entirely. If the recesses along the edge of a simple sheet do not reach a quarter of the half-width of the sheet plate, then such a simple sheet is called solid. A compound leaf consists of several leaflets located on a common petiole (called a rachis). Leaflets, in addition to their leaf blade, may also have their own petiole (which is called petiole, or secondary petiole). In a complex sheet, each plate falls off separately. Since each leaflet of a compound leaf can be considered as a separate leaf, it is very important to locate the petiole when identifying a plant. Compound leaves are characteristic of some higher plants such as legumes.

Simple Leaf (Aspen) Compound Leaf (Horse Chestnut)

In palmate (or palmate) leaves, all leaf blades diverge along the radius from the end of the root like the fingers of a hand. The main petiole is missing. Examples of such leaves are hemp (Cannabis) and horse chestnut (Aesculus).

In pinnate leaves, leaf blades are located along the main petiole. In turn, pinnate leaves can be pinnate, with an apical leaf blade (example - ash, Fraxinus); and paired, without an apical plate (example - mahogany, Swietenia).

In bipinnate leaves, the leaves are divided twice: the plates are located along the secondary petioles, which in turn are attached to the main petiole (an example is Albizia, Albizzia).

Three-leaved leaves have only three blades (example - clover, Trifolium; bean, Laburnum)

Pinnately incised leaves resemble pinnate, but their blades are not completely separated (example - some mountain ash, Sorbus)

Depending on the location of the leaflets, pinnate leaves and palmate leaves are distinguished. In the first, the leaves are arranged in two rows on both sides of the rachis, which is an overgrown elongated petiole. Classic palmately compound leaf in horse chestnut (Aesculus) species. The palmately complex and their particular case - there are no trifoliate rachis leaves and the leaves extend from the top of the petiole. According to the degree of branching of the rachis, single-, double- and thrice-pinnate leaves are distinguished. If the rachis of any order of a pinnate leaf ends at the apex with an unpaired leaflet, the leaf is unpaired pinnately compound, in the absence of leaflets, it is paired pinnately compound. The thrice unpaired pinnate leaf type is known only in one plant - the tropical species Moringa pterygosperma (Moringa pterigosperma). Doubly-pinnately compound leaves are very common in representatives of the mimosa subfamily (legume family). The number of small leaves of such a sheet sometimes reaches 10 thousand.

Outwardly, the leaves of some plants are very similar to simple leaves. However, it should be remembered that in the axils of the leaves (both simple and complex) there is an axillary bud, but there is no leaflet in the axil. The leaves depart from the stem in different planes, and the leaves from the rachis in one.

Types of dismemberment of a plate of a simple sheet

The leaf blade of a simple leaf can be whole or, on the contrary, dissected, i.e. in varying degrees, indented, consisting of protruding parts of the plate and notches.

A simple leaf has 1 petiole and 1 leaf blade, albeit heavily indented. A compound leaf consists of several separate plates, called leaflets, which are attached with their petioles to a common main petiole.

Fig.2. Special forms of leaf blades. 1 - needle-shaped, 2 - heart-shaped, 3 - kidney-shaped, 4 - swept, 5 - spear-shaped, 6 - sickle-shaped.

Depending on the nature and depth of dissection of the plate, the leaves are lobed, separate or dissected.

A simple leaf is never divided into separate, sharply demarcated segments called leaflets. A compound leaf, such as that of horse chestnut or most legumes, on the contrary, is divided into leaflets, each of which is usually provided with its own small petiole. There are two main types of compound leaves - pinnate and palmate. In pinnate leaves, leaflets are located on both sides of the main axis, or rachis, which is a continuation of the petiole. All leaflets of a palmately compound leaf depart from the top of the petiole, and they have no rachis. The leaflets of typical compound leaves are articulated.

Fig.3. Types of division of simple leaf blades and classification of compound leaves

The leaf blade of a simple leaf can be whole or, on the contrary, dissected, i.e. in varying degrees, indented, consisting of protruding parts of the plate and notches. To determine the nature of dissection, the degree and shape of the indentation of leaf blades and the correct name of such leaves, first of all, one should take into account how the protruding parts of the blade - lobes, lobes, segments - are distributed in relation to the petiole and to the main vein of the leaf. If the protruding parts are symmetrical to the main vein, then such leaves are called pinnate. If the protruding parts come out as if from one point, the leaves are called palmate. According to the depth of cuts of the leaf blade, leaves are distinguished: lobed, if the recesses (the depth of the cuts) do not reach half the width of the half-plate (the protruding parts are called lobes); separate, with a depth of cuts that go deeper than half the width of the half-plate (protruding parts - lobes); dissected, with a depth of incisions reaching the main vein or almost touching it (protruding parts - segments).

Forms of simple leaves and their sizes

The leaves of a simple form consist of one leaf plate, attached to one petiole. They have solid edges or cut in the form of teeth, notches, notches (small or large, sharp, blunt, uniform or heterogeneous). The simplest forms have leaves with solid leaf plates:

The linear form of the leaf (Fig. 4) is most characteristic of herbaceous plants of the family of cereals, sedges, rushes, irises. The leaf of this form is long and narrow, the venation is usually linear, unbranched, longitudinal. There are forms more or less wide (broad-linear and narrow-linear), more often with solid edges or slightly ribbed or serrated.

Fig.4 Linear form of the sheet. Fig.5. Lanceolate leaf shape.

The lanceolate form got its name because of the similarity with the surgical instrument - the forerunner of the scalpel - the lancet. Such a leaf is shorter than the linear one, expanded towards the base and narrowed towards the top, the venation is branched. Also, depending on the width relative to the length, there are wide-, narrow- and oblong-lanceolate, and forms that combine linear and lanceolate features are called linear-lanceolate. Lanceolate leaves are found in various types of grasses and trees (eg sea buckthorn, sucker, willow, bedstraw, etc.).

Rounded leaves, as a rule, have a fairly branched venation. Their edges can be either solid or serrated, serrated, wavy. It occurs in trees (alder, aspen) and herbaceous plants (budra) (Fig. 6). A rounded shape, elongated in length, is called elliptical (large plantain, tarry, etc.). When describing plants, oval leaves are called leaves that have a shape, as in Fig. 7:

Fig.6. Round leaf shape. Fig.7. Oval leaf shape.

The ovoid shape of the leaves is quite common in nature, as, for example, in many trees of the Rosaceae family: quince, apple, cherry, shadberry, etc. Usually, the ovate leaves are expanded at the base and taper towards the top, if vice versa, then this shape is called obovate ( fig.8,9):

Fig.8. Egg-shaped leaf. Fig.9. Obovate leaf shape.

When rounded leaves have a pronounced indentation at the petiole or on top and the leaf blade resembles a heart in contour, they are respectively called heart-shaped and obverse heart-shaped. When the cut is deeper and all the edges of the leaf plate are rounded so that it resembles a kidney in shape, it is not difficult to guess that they are called kidney-shaped (Fig. 10):

Fig.10. Reniform leaf shape. Fig.11. Palmate form

The palmately divided leaf plate is dissected from the edge towards the petiole to half, two thirds or three quarters, etc. sheet diameter. The separate protrusions thus formed are called leaf lobes. The shape of leaf lobes is described according to the principles mentioned earlier, i.e. they may be lanceolate, linear, spear-shaped, pointed or blunt at the ends, etc. Each leaf share has its own central, usually well-marked vein, which branches into smaller ones. The main veins radiate from the base of the leaf to its edges (Fig. 12). The border of leaf lobes, as well as in whole leaves, can be smooth, wavy, serrated, serrate.

The palmately lobed form of the leaf is similar to the palmately divided, but the leaf lobes are wider and, accordingly, fewer in number. If the leaf plate is radially divided into lobes almost to the very base, then such leaves are called palmately dissected (Fig. 13).

Fig.12. Palmate leaf shape. Fig.13. palmately dissected

The group of pinnate leaf forms, in contrast to the palmate ones, has only one main, largest, vein that branches into several orders of smaller veins in the leaf lobes and passes into the petiole, and the outlines of such leaves resemble bird feathers. The most characteristic forms of pinnate leaves are: pinnate (Fig. 14), pinnate (Fig. 15) and lyre-shaped (Fig. 16), which has a wide rounded plate at the top and narrower and smaller in length, gradually decreasing towards the base.

Fig.14 Fig.15 Fig.16

The leaf lobes of the palmate and pinnate leaves, in turn, can be once again deeply dissected into smaller, and sometimes the same size leaf lobes of the second and third order. In such cases, the leaves are defined as twice - or thrice palmately divided (- palmately lobed, - palmately dissected, - pinnatipartite, and so on).

The following is another scheme for classifying simple leaves according to shape, which is found in some sources:

1. Broadly ovate leaf

2. Rounded

3. Reverse broad ovoid

4. Ovate

5. Elliptical

6. Obovate

7. Narrow ovoid

8. Lancet

9. Oblong

10. Reverse narrow ovoid

11. Linear

General conclusion

The size of the leaves most often ranges from 3 to 10 cm, however, giant leaves of some palm trees up to 15 m long are known. The largest leaves of the famous Amazonian water lily Royal Victoria (Victoria regia) reach 2 m in diameter. The size, shape and degree of dissection of the leaves, although they are hereditary features of a particular species, are very variable and also depend on the living conditions of its individuals.

Botanists unanimously recognized the smallest plant on Earth as rootless wolf, which is found in freshwater bodies of Australia, the tropics of the Old World and the temperate zone of the northern hemisphere. Several reduced wolfia leaves, together with a single-stamen flower, have a total size of 0.5-2 mm.

The largest leaves.

Here, of course, palm trees are beyond competition. In Sri Lanka, it is the umbrella coryphe palm. The blades of its fan-shaped leaves reach 8 m in length and 6 m in width. One such sheet can cover half of the volleyball court. Even larger are the feathery leaves of the Brazilian raffia tedigera palm. On a petiole 4-5 m long, a "giant feather" sways over 22 m long and almost 12 m wide. One such leaflet can serve as a blanket for 10 people at the same time. And if you put it on the ground vertically, it will rise above a six-story building.

1. Korovkin O.A. Anatomy and morphology of higher plants: a dictionary of terms. - M.: Bustard, 2007. - 268, p. - (Biological sciences: Dictionaries of terms). - 3000 copies. - ISBN 978-5-358-01214-1

2. Lotova L.I. Botany: Morphology and anatomy of higher plants: Textbook. - 3rd, correct. - M.: KomKniga, 2007. - S.221-261.

3. Lyubimenko V. Influence of light on the assimilation of organic substances by green plants // Proceedings of the Imperial Academy of Sciences. VI series. - 1907. - No. 12. - S.395-426, from 6 tab.

4. Malinovsky V.I. Physiology of plants. Proc. allowance. - Vladivostok: FENU Publishing House, 2004.

5. Fedorov Al.A., Kirpichnikov M.E. and Artyushenko Z.T. Atlas on the descriptive morphology of higher plants. Liszt / Academy of Sciences of the USSR. Botanical Institute named after V.L. Komarov. Under total ed. member - cor. Academy of Sciences of the USSR P.A. Baranov. Photos by V.E. Sinelnikov. - M. - L.: Publishing House of the Academy of Sciences of the USSR, 1956. - 303 p. - 3,000 copies.

6. Hall D., Rao K. Photosynthesis: Per. from English. - M.: Mir, 1983.

7. http://www.floriculture.ru/rast/razn/morf/list. shtml

8. http://ru. wikipedia.org/wiki/Sheet

LEAF - LATERAL SHOOTING organ

General characteristics of the sheet

Sheet- flattened lateral organ of the shoot with bilateral symmetry; it is laid in the form of a leaf tubercle, which is a lateral protrusion of the shoot. The leaf rudiment increases in length due to the growth of the apex and in width due to marginal growth. In seed plants, apical growth quickly stops. After the deployment of the kidney, there is a multiple division of all leaf cells (in dicotyledons) and an increase in their size. After differentiation of meristem cells into permanent tissues, the leaf grows at the expense of the meristem at the base of the leaf blade. In most plants, the activity of this meristem ends quickly, and only in a few, such as clivia, amaryllis, continues for a long time.

In annual herbaceous plants, the life span of the stem and leaf is almost the same - 45-120 days, in evergreens - 1-5 years, in conifers, such as fir - up to 10 years.

The first leaves of seed plants are represented by the cotyledons of the embryo. The next (true) leaves are formed in the form of meristematic tubercles - primordians, arising from the apical meristem of the shoot.

The leaf performs three main functions: photosynthesis, gas exchange and transpiration. In addition, it can be an organ of protection (scales, spines), attachment to a support (antennae), a supply of nutrients and water, as well as vegetative propagation.

The main functions of a leaf are photosynthesis, transpiration and gas exchange.

leaf morphology.

The main part of the sheet is leaf blade. The lower part of the leaf, articulated with the stem, is called basis sheet. Quite often, a stem-like cylindrical or semicircular in section is formed between the base and the plate. petiole sheet. In this case, the leaves are called petiolate, Unlike sedentary leaves without petiole. The role of the petiole, in addition to supporting and conducting, is that it retains the ability to intercalate growth for a long time and can regulate the position of the plate, bending towards the light.

The base of the sheet can take a different shape. Sometimes it is almost imperceptible or looks like a slight thickening ( leaf pad), for example, sour. Often the base grows, covering the entire node and forming a tube called vagina sheet. The formation of a sheath is especially characteristic of monocots, in particular for cereals, and from dicots, for umbrellas. The sheaths protect the interstitial meristems at the base of the internodes and the axillary buds above the nodes.

Often the base of the leaf gives paired lateral outgrowths - stipules. The shape and size of the stipules are different in different plants. In woody plants, stipules usually look like membranous scaly formations and play a protective role, constituting the main part of the kidney integuments. At the same time, they are short-lived and fall off when the buds expand, so that stipules are not found on an adult shoot in fully developed leaves (birch, oak, linden, bird cherry). Sometimes the stipules are green in color and function along with the leaf blade as photosynthetic organs (many legumes and rosaceae).

All representatives of the buckwheat family are characterized by the formation bells. The bell is formed by the fusion of two axillary stipules and surrounds the stem above the node in the form of a short membranous tube.

The main part of the assimilating leaf is its lamina. If a leaf has one plate, it is called simple. At complex leaves on one petiole with a common base there are two, three or more separate plates, sometimes with their own petioles. Individual records are called leaflets complex sheet, and the common axis carrying the leaves is called rachis. Depending on the location of the leaves on the rachis, they distinguish pinnate- and palmately complex leaves. In the first, the leaves are arranged in two rows on both sides of the rachis, which continues the petiole. The palmately compound leaves do not have rachis, and the leaflets extend from the top of the petiole. A special case of a complex sheet - ternary.

Rice. Sheet parts (diagram): 1 - petiolate leaf; 2 - sessile leaf; 3 - sheet with a small pillow at the base; 4 - vaginal leaves; 5 - leaf with free stipules; 6 - leaf with stipules adhering to the petiole; 7 - leaf with axillary stipules; Pl- plate; os- base; Vl- vagina; Etc- stipules; H- petiole; PP- axillary kidney; THEM- intercalary (intercalary) meristem.

Rice. Compound leaves (diagram): A - unpaired pinnate; B - paired pinnate; B - ternary; G - palmately complex; D - doubly paroperistoslozhny; E - twice unpaired pinnate; 1 - leaflet; 2 - petiole; 3 - rachis; 4 - petiole; 5 - stipules; 6 - rachis of the second order.

The process of forming a complex leaf resembles branching, which can go up to the second or third order, and then twice and thrice pinnate leaves. If the rachis ends with an unpaired leaf, the leaf is called unpaired pinnate if a couple of leaves - paired pinnate.

When characterizing a leaf blade, a number of features are taken into account: the general outlines (contours) of the leaf, the shape of the base and top, the shape of the edge, venation, the nature of the surface, consistency and other features.

The leaf blade or leaflet may be whole or dismembered more or less deep blades, shares or segments, located at the same time pinnate or palmately. Distinguish pinnate- and palmate-lobed, pinnate- and palmately divided and pinnate- and palmately dissected leaves . There are twice, thrice and repeatedly dissected leaf blades.

The forms of whole leaf blades and dissected leaves in general outline are distinguished depending on two parameters: the ratio between length and width and in which part of the blade its greatest width is located.

Rice. Forms of leaf blades: 1 - needle; 2 - heart-shaped; 3 - kidney-shaped; 4 - swept; 5 - spear-shaped; 6 - crescent.

When describing, also pay attention to the shape of the top, base and edge of the plate. .

Rice. The main types of tops, bases and edges of leaf blades: A - tops: 1 - sharp; 2 - pointed; 3 - dull; 4 - rounded; 5 - truncated; 6 - notched; 7 - pointed; B - bases: 1 - narrow wedge-shaped; 2 - wedge-shaped; 3 - wide wedge; 4 - descending; 5 - truncated; 6 - rounded; 7 - notched; 8 - heart-shaped; B - edge of the sheet: 1 - serrate; 2 - doubly serrated; 3 - gear; 4 - crenate; 5 - notched; 6 - solid.

Leaves

It is easier to identify trees and shrubs by leaves than by other organs. The flowers and fruits of many tree species are inconspicuous, located high. Their flowering time often coincides with school holidays, which makes it difficult to display and collect natural material. The leaves of the trees are usually large with clear morphological features. The shape of the leaves is more or less characteristic of each plant species.

Classes can be held partially in the classroom when studying the external structure and shape of leaves, during extracurricular activities, before and after excursions to the forest, parks, squares, as well as on excursions, in summer pioneer camps.

Purpose of the lesson

Observe, describe and compare the morphological characteristics of leaves in various trees and shrubs.

To instill in schoolchildren some skills in using determinants (acquaintance with signs, terms). Develop observation.

Equipment

For every student: sets of dry leaves under the numbers in the folders; description plan; lists of plants; tasks; simple pencils with an elastic band; tweezers, magnifiers.

For the whole class: instructive visual aids - drawings of the forms of simple and complex leaves, bases, tops, edges, venation, dismemberment of the leaf blade; herbaria and collections of leaves and shoots.

hardwood

In autumn, without damaging the plants, you can easily collect fallen leaves, dry them in presses, under an iron. This will be a good material that can be used throughout the school year, especially in winter when going through the topic "Leaf". It is better to distribute the leaves to the students not sewn in order to see the underside of the sheet. Sets of leaves are well placed in folders with pockets.

You need to get acquainted with the basic concepts of leaf morphology in the previous lesson. When describing leaves, it is necessary to analyze as many morphological features as possible for the development of observation, taking into account that often leaves in shape and other features even on the same annual shoot, but in different places can differ significantly from each other. The variability of the form of aspen leaves is shown in fig. 2.

Plan for describing trees and shrubs by leaves

1 - sheet simple or complex; 2- sheet petiolate or sessile; 3- leaf blade shape: a) simple leaves - round, oval, oblong, lanceolate, linear, ovate, obovate; b) compound leaves - pinnately compound (paired and unpaired), palmately compound; four - leaf base shape: wedge-shaped, rounded, heart-shaped; 5 - leaf tip shape: dull, acute; 6- venation: pinnate, palmate; 7- dissection of the leaf blade: whole, lobed, separate, dissected; eight - blade edge shape: entire, serrated, serrate, crenate, notched; 9 - color, shine, pubescence and other features (Tables VI, VII).

To describe the leaves, it is necessary to have special notebooks in which to write down only the answers to the questions of the plan, putting down their numbers. In this case, it is necessary to give drawings of leaves from nature. Answers can be arranged in the form of a table; then the same characters in different plants fall into the same column and can be easily compared with each other. Assignments for independent work are best given in writing.

Let us give examples of the description of leaves in the order of the questions of the plan (see tables III, IV, V).

Linden small-leaved. 1 - simple; 2 - petiolate; 3 - ovoid; 4 - heart-shaped; 5 - pointed with an oblique top; 6 - palmate; 7 - whole; 8 - crenate-toothed, entire in the lower half; 9 - dark green above, glabrous, soft-haired below.

Oak summer, ordinary, or pedunculate. 1 - simple; 2 - petiole 3 - 7 mm; 3 - oblong-obovate; 4 - narrowed into petiole; 5 - blunt or notched; 6 - pinnate; 7 - bladed, 4 - 7 blunt blades; 8 - whole; 9 - dark green above, shiny, bluish-green below, glabrous on both sides.

Birch warty, or drooping. 1 - simple; 2 - petiole half as long as leaf blade, 15 - 30 mm; 3 - triangular-ovate or rhomboid, leaf blade length 30 - 70 mm, width 25 - 50 mm; 4 - straight cut or at an angle of 120 °, sometimes slightly heart-shaped; 5 - acute; 6 - pinnate; 7 - whole; 8 - solid-extreme at the bottom, double-serrated at the top; 9 - naked on both sides.

Mountain ash. 1 - complex, pinnate, leaflets 11 - 21; 2 - petiole 80 - 170 mm, naked or hairy; 3 - oblong; 4 - unequal at the base; 5 - acute; 6 - pinnate; 7 - whole; 8 - solid in the lower part, serrated above; 9 - dark green above, bare, gray below.

Acacia yellow, or caragana. 1 - complex, paired, 4 - 8 pairs of leaflets; 2 - petiolate, common petiole 50 - 80 mm, there are stipules leathery, prickly; 3 - oval; 4 - wedge-shaped; 5 - sharp with a bristle; 6 - pinnate; 7 - whole; 8 - whole; 9 - naked, hairy in youth.

Comparison tasks

1. Let's compare the leaves of viburnum ordinary and Siberian hawthorn. What are the similarities and differences? (Table VIII).

similarity Leaves are simple, petiolate. Leaf blades are ovoid (hawthorn is obovate); with pinnate venation, lobed. difference: the base of the leaf blade in hawthorn is wedge-shaped, in viburnum it is rounded. The hawthorn has more blades, the viburnum often has three. In hawthorn, the leaf is covered on both sides with short hairs; in viburnum, it is naked, wrinkled from above, and fluffy from below. In hawthorn, stipules are larger, in viburnum - filiform.

2. Let us compare the compound leaves of common ash, ash-leaved or American maple, and red elderberry (see Table VIII).

similarity Leaves are compound, pinnate, with pinnate venation. difference: ash has the largest leaf, 7-15 leaves; leaf length is up to 40 cm, common petiole up to 15 - 25 cm. Lateral leaves almost sessile. Ash-leaved maple has 3-5, less often 7 leaves. Common petiole 10 - 22 cm and lateral leaflets have petioles. The red elderberry has 5 - 7 leaves, the common petiole is 5 - 11 cm with two stipules. The leaves are almost sessile. Leaves with a slight odor.

Common ash has an obovate upper leaflet. Lateral leaflets lanceolate, cuneate at base. In the ash-leaved maple, the upper leaflet is ovate-lanceolate, unequal; wedge-shaped base. In the first pair, the leaves are lanceolate, cuneate at the base, they are especially similar to ash leaves. In the second pair, leaflets are broadly ovate-lanceolate. The red elderberry leaves are almost sessile, oblong-oval with an oblique pointed apex, unevenly rounded at the base.

Let us compare the dissection and shape of the edge of the leaf blades: in the common ash and the red elderberry, the leaf blade is intact, while in the ash-leaved maple the middle leaflet and the lower lateral ones are often lobed. The shape of the edge of the leaf blades: in ash, serrated or crenate-serrated; in elderberry - serrated; in the ash-leaved maple, the lateral leaves are whole or with sparse teeth; upper - large-toothed.

3. Compare the leaves of the common elm, hazel, gray alder, hornbeam (see Table VIII).

What do these leaves have in common and what is the difference?

similarity: leaves are simple, petiolate, with pinnate venation, with a whole leaf blade (sometimes almost lobed in hazel), with a sharp apex, not entire. difference: Elm has the shortest hairy petiole 4 - 5 mm; at hazel 10 mm with glandular bristles; at the hornbeam 10 - 15 mm, long-haired, often glandular; in gray alder 10 - 25 mm, naked. Leaf blade of gray alder 40 - 90 mm(oblong-ovoid), in smooth elm oval or obovate. Lack of equilateralness at the base of the leaf blade is most often and stronger in the elm, and also occurs in the hornbeam. In gray alder, the leaf base is rounded or wedge-shaped. The edge of the leaf in the smooth elm is serrated, in hazel, gray alder and hornbeam - serrated (in alder with large prominent teeth). The upper side of all leaves is dark green, but in gray alder and hornbeam it is naked, in hazel it is finely hairy, rough with depressed nerves, in elm it is rough. The underside of the leaves of gray alder is covered with gray felt over the entire surface; at the hornbeam - naked; in hazel it is hairy, sometimes with glandular bristles, in elm it is soft hairy.

Exercise: draw from memory the leaves of birch, maple, elm, hawthorn, viburnum. Who will draw faster and more correctly. Write the name of the plants under the drawings of the leaves.

Review questions

1. What tree and shrub species have simple leaves?

Answer: poplar, linden, aspen, hazel, Tatar maple, hawthorn, viburnum, etc.

2. What tree and shrub species have compound leaves?

Answer: pinnate: ash-leaved maple, common ash, common mountain ash, common rosehip, red elder, white acacia, etc.; parenpinnate: yellow acacia, honey locust.

3. Name simple leaves with palmate venation.

Answer: balsam poplar, small-leaved linden, maple, holly, etc.

4. Name simple leaves with pinnate venation.

Answer: oak, birch, Tatar maple, hornbeam, alder, hazel (hazel), etc.

5. Name the leaves simple with a whole leaf blade.

Answer: balsam poplar, small-leaved linden, elm, warty birch, Tatar honeysuckle, hornbeam, aspen, alder (hazel), etc.

6. Name the leaves simple lobed.

Answer: summer oak, Norway maple, ginnala maple, Siberian hawthorn, common viburnum, etc.

7. Name the leaves simple, entire.

Answer: oak, Tatar honeysuckle, brittle buckthorn, etc.

8. Name the leaves with a serrated edge of the leaf blade.

Answer: balsam poplar, small-leaved linden (entire-edged in the lower half, crenate-toothed above), aspen, etc.

9. Name the leaves with a notched-toothed shape of the edge of the leaf blade.

Answer: Norway maple, etc.

10. Name the leaves with a serrated edge of the leaf blade.

Answer: warty birch, mountain ash, red elderberry, ginnal maple, Tatar maple, etc.

11. What are the forms of leaf blades of summer oak, warty birch, Norway maple, small-leaved linden?

Answer: obovate, triangular-ovate, rounded, ovoid.

12. In which leaves does the base of the leaf blade have a heart-shaped shape?

Answer: in small-leaved linden, Norway maple, etc.

13. Which leaves are unequal at the base?

Answer: smooth elm leaves, etc.

14. What are the similarities and differences between the leaves of warty birch and downy birch?

Answer: similarity - leaves are simple, petiolate, with pinnate venation, the length is the same; the difference is that the shape of the leaf blade in the warty birch is often triangular-ovate or rhombic, the base is wedge-shaped or truncated, less often rounded, and in the fluffy birch the shape of the leaf blade is ovoid or oval, the base is round, heart-shaped, less often narrowed. The shape of the top of the leaf of the warty birch is long-pointed, and that of the downy birch is short-pointed. The shape of the edge of the warty birch is sharply serrated, and that of the downy birch is coarsely serrated. The warty birch has bare leaves, while the fluffy birch has young leaves densely pubescent and the pubescence on the petiole remains for a long time.

conifers

The leaves of conifers are most often in the form of needles, less often in the form of scales (cypress, thuja). They can be on the run spirally(singly, in pairs, in bunches, in two rows), for example: spruce, pine, Siberian cedar, fir; opposite(crosswise), for example: cypress, western thuja; whorled(three-four-membered whorls), for example: juniper. In some conifers, the shoots on which the leaves are located are divided into elongated and shortened ones, for example, pine, Siberian cedar, larch); other species (spruce, fir) have only elongated shoots. Shortened shoots grow insignificantly during one summer, and elongated shoots grow by 35 cm and even more. Sometimes shortened shoots develop into elongated ones.

The needles are annual, soft, dying off in the autumn of the first year (for example, in larch) and hard, long-term, it dies off no earlier than the autumn of the second year.

The plan for the description of conifers by needles

1 - arrangement of needles: spiral (singly, in pairs, bundles, two-row), opposite (crosswise), whorled (three-four-membered whorls); 2- shape, size and etc.; 3- color, shine and other features (see Table II).

We give examples of the description of the leaves of conifers in the order of the questions of the plan.

Scotch pine. 1 - spiral, steam needles, coming out of the brown-gray leathery sheath; 2 - semi-cylindrical or semi-circular, sharp at the end, finely serrated along the edges, rigid, strongly twisted; 3 - dark green on the upper convex side, and on the lower grooved side - bluish or whitish; stomata are located on the lower side.

Siberian cedar. 1 - spiral, 5 pieces in bundles, which are surrounded by a yellow-brown early falling sheath; bundles are close to each other; the needles are densely located on the shoot; 2 - trihedral, serrated along the edges, size 11 cm; 3 - bright or dark green, hard.

Siberian larch. 1 - spiral, on shortened shoots and old trees - in bunches from 25 to 50 pcs. in a bunch, and on elongated and young trees singly along the entire shoot; the size of the needles increases from the top to the base of the shoot, which is often surrounded by a crown of the longest needles; needle size 30 - 35 mm; 2 - narrowly linear, flat, slightly widened towards the apex, with blunt ends; 3 - bright green with a bluish bloom, the needles are soft, tender; stomata are arranged in rows on both sides.

Norway spruce. 1 - spiral, singly around the shoot and directed in all directions; 2 - tetrahedral, short, hard, thin, prickly, length - 15 - 25 mm; 3 - dark green, shiny, sits densely, raised up.

Siberian fir. 1 - spiral, singly, directed to two opposite sides in a comb-like manner; 2 - flat, with a rib in the middle and two white stripes of stomatal rows; length up to 30 mm; 3 - the upper side is dark green, shiny, the lower side is paler; young fir shoots have a light, yellowish-green color; the needles are soft, narrow, sitting densely; the end is blunt with a notch, so the needles are not prickly.

Review questions

What is the difference between the needles of Siberian cedar and Scotch pine?

Answer: cedar needles are much longer, softer than those of pine, and are arranged in bunches of five needles (in pine - of two needles).

2. With what coniferous species does Siberian larch have some similarity in the form of needles?

Answer: with spruce, but larch needles are much narrower and longer, and besides, they are soft and have a lighter tone.

3. What is the difference between fir and spruce needles?

Answer: fir needles have pronounced upper and lower sides of different colors, it is flat, wide, while spruce needles are tetrahedral and the sides are difficult to distinguish; if fir needles are rubbed between the fingers, it gives off a balsamic smell reminiscent of the smell of lemon peel. The needles are located on the shoot of the fir scallop-shaped on two opposite sides, and of the spruce in all directions.

4. From the needles of which tree is a valuable essential oil for the perfume industry produced?

Answer: from fir needles.