All plants are composed of vegetative and generative organs. The latter are responsible for reproduction. In angiosperms, this is a flower. It is the vegetative organs of the plant - the root system and shoots. Root system consists of a main root, lateral and additional. Sometimes main root may not be expressed. This system is called fibrous. Shoots are composed of stems, leaves and buds. The stems provide transport of substances and also support the position of the plant. The buds are responsible for the formation of new shoots as well as flowers. The leaf is the most important plant organ as it is responsible for photosynthesis.
How does it work
Consist of several types of fabrics. Let's take a closer look at them.
From the point of view of histology
Above is the epidermis. This layer is one or two cells thick with dense membranes located very close to each other. This fabric protects the sheet from mechanical damage, and also prevents excessive evaporation of water from the organ. In addition, the epidermis is involved in gas exchange. For this, stomata are present in the tissue.
On top of the epidermis there is also an additional protective layer, which consists of wax secreted by the cells of the integumentary tissue.
Under the layer of the epidermis there is a columnar, or assimilatory parenchyma. This is a leaf. The process of photosynthesis takes place in it. The cells of the parenchyma are arranged vertically. They contain a large number of chloroplasts.
Under the assimilation tissue is the leaf vascular system, as well as the spongy parenchyma. are xylem and phloem. The first consists of vessels - dead cells connected vertically to each other, without horizontal partitions. Through the xylem, water with substances dissolved in it enters the leaf from the root. Phloem also consists of - elongated living cells. On this conductive tissue, solutions are transported, on the contrary, from the leaf to the root.
The spongy tissue is responsible for the gas exchange and evaporation of water.
Below these layers is the lower epidermis. It, like the top one, performs a protective function. It also has stomata.
Leaf structure
A petiole departs from the stem, on which the leaf blade is attached - the main part of the leaf. Veins extend from the petiole to the edges of the leaf. In addition, stipules are located in its junctions with the stem. Complex leaves, examples of which will be considered below, are arranged in such a way that there are several leaf plates on one petiole.
What are the leaves
Depending on the structure, simple and complex leaves can be distinguished. Simple ones consist of one plate. A compound sheet is one that consists of several plates. It can be varied in structure.
Types of compound leaves
There are several types of them. Factors for dividing them into types can be the number of plates, the shape of the edges of the plates, as well as the shape of the leaf. There are five types of it.
Leaf shape - what it is
There are such types of it:
- arrow-shaped;
- oval;
- annular;
- linear;
- heart-shaped;
- fan-shaped (semicircular leaf);
- pointed;
- needle-like;
- wedge-shaped (triangular leaf, attached to the stem at the top);
- spear-shaped (sharp with thorns);
- spatula;
- lobed (the leaf is divided into several blades);
- lanceolate (long, wide leaf in the middle);
- reverse lanceolate ( top part the sheet is wider than the lower one);
- obverse-heart-shaped (heart-shaped leaf, attached to the stem with a sharp end);
- diamond-shaped;
- sickle.
A composite sheet can have plates of any of the listed shapes.
The shape of the edges of the plates
This is another factor that allows you to characterize a complex sheet.
Depending on the shape of the edges of the plates, the leaves are of five types:
- toothed;
- crenate;
- serrated;
- notched;
- all-edge.
Other types of compound leaves
Depending on the number of plates and their location, the following types of complex leaves are distinguished:
- finger-like;
- feathery;
- two-pinnate;
- three-leafed;
- perforated.
In complex finger-like leaves, all plates diverge along the radius from the petiole, resembling the fingers of a hand in their appearance.
Cirrus leaves have leaf plates along the petiole. They are divided into two types: paired and unpaired. The first ones do not have an apical plate; their number is a multiple of two. In pinnate, the apical plate is present.
In two-pinnate leaves, the plates are located along the secondary petioles. Those, in turn, are attached to the main thing.
Three-leafed have three plates.
Perstoned leaves are similar to pinnate.
Compound leaves - their venation
There are three types of it:
- go exactly from the base of the sheet to its edges along the entire plate.
- Arc. The veins are not straight, but in the form of an arc.
- Mesh. It is divided into three subspecies: radial, finger and pinnate. With radial venation, the leaf has three main veins, from which the rest branch off. Finger is characterized by the presence of more than three main veins, which are separated near the base of the petiole. With pinnate, the leaf has one main vein, from which the rest extend.
Most often, a composite leaf has a reticular venation.
Arrangement of leaves on the stem
Both simple and complex leaves can be arranged in different ways. There are four types of location:
- Whorled. The leaves are attached in three pieces to a narrow stem - a whorl. They can be cross, with each whorl being rotated 90 degrees relative to the previous one. Plants with this arrangement of leaves are elodea, raven eye.
- Rosette. All leaves are at the same height and are arranged in a circle. Agave, chlorophytum have such rosettes.
- Sequential (regular). Leaves are attached, one for each node. Thus, they are located near birch, pelargonium, apple, rose.
- The opposite. With this type of arrangement, there are two sheets at each node. Each node is usually rotated 90 degrees relative to the previous one. Also, the leaves can be arranged in two rows without turning the nodes. Examples of plants with such an arrangement of leaves are mint, jasmine, lilac, fuchsia, lamb.
The first two types of leaf arrangement are characteristic of plants with simple leaves. But the second two types can also refer to complex leaves.
Examples of plants
Now let's consider different kinds complex leaves with examples. They are allocated in sufficient quantity. Plants with complex leaves can be of various life forms. It can be both bushes and trees.
Ash trees are very common plants with complex leaves. These are trees of the olive family, dicotyledonous class, angiosperm division. They have odd-pinnate compound leaves with seven to fifteen plates. The shape of the edge is serrated. The venation is reticulated. Ash leaves are used medicinally as a diuretic.
A striking example of a bush with complex leaves is raspberry. These plants have odd-pinnate leaves with three to seven plates on long petioles. The type of venation is pinnate. The shape of the leaf edge is crenate. Raspberry leaves are also used in folk medicine... They contain substances that have an anti-inflammatory effect.
Another tree with complex leaves is rowan. Her leaves are paired. The number of plates is about eleven. Venation is peristonerous.
The next example is clover. It has complex, trifoliate leaves. The venation of the clover is reticulate. The shape of the leaf edge is whole-edged. In addition to clover, the legume also has trifoliate leaves.
Complex leaves also have a plant such as albicia. It has two-leafed leaves.
Another vivid example plants with complex leaves - acacia. This bush has a net venation. Edge shape - all-edge. Leaf type - two-pinnate. The number of plates is from eleven pieces.
Another plant with complex leaves is strawberry. Leaf type - three-leafed. The venation is reticulated. These leaves are also used in traditional medicine. Usually with atherosclerosis and other vascular diseases.
Conclusion
As a conclusion, we present a summary table of complex leaves.
| Complex sheet type | Description | Examples of plants |
| Finger leaves | The plates fan out from the petiole, resembling human fingers | Horse chestnut |
| Pinnate | The number of plates is odd, there is an apical one. All plates are located along the main petiole | Ash, rose, rowan, acacia |
| Paired | The number of leaf plates is odd, the apical one is absent. All of them are located along the main petiole. | Peas, sweet peas |
| Bifinous | The blades are attached to secondary petioles growing from the main petiole. | Albicia |
| Triplets (three-leafed) | They have three plates that extend from the main petiole | Clover, bean |
| Perstoning | The plates are arranged in a pinnate type, but not completely separated. | Rowan |
So we examined the structure of a complex sheet, which they possess.
Sheet- part of the escape. Outwardly, the leaves of different plants are very different, but they have a lot in common. The leaves of most plants are green in color and consist of leaf blade and petiole by which they are connected to the stem.
In some plants, the veins are parallel to one another. Such venation are called parallel. It is found in many monocotyledonous plants. Arc venation is also characteristic of monocotyledonous plants.
Have dicotyledonous plants veins branch many times and form a continuous network. This mesh venation.
But there are exceptions. For example, in a raven-eye monocot plant, the leaves have a net venation. 
If there is one leaf blade on the petiole, the leaf is called simple.
A leaf consisting of several leaf blades connected to a common petiole by small petioles is called complicated... In such leaves, each blade usually falls off independently of the others.
Let's get acquainted with the internal structure of the leaf blade. The leaf blade consists of many cells different sizes and forms, that is, it has cellular structure... On the upper and lower sides, the leaf is covered with more or less identical cells, tightly adjacent to one another. These are the cells of the skin that covers the leaf and protects it from damage and drying out. Skin- one of the types of plant integumentary tissue. The cells of the skin are colorless and transparent, but among the colorless cells are located in pairs green guard cells. There is a gap between them. These cells and the gap between them are called stomata... Through the stomatal gap, air penetrates into the leaf and water vapor, oxygen and carbon dioxide are released into the atmosphere.
In most plants, stomata are found only in the skin of the underside of the leaf blade.
Under the skin are the cells of the leaf pulp. The pulp of a leaf consists of several layers of cells. One of the layers is directly adjacent to the upper skin. Its cells resemble rather equal columns. They are especially rich in chloroplasts. The deeper lie the more rounded or irregular shape cells; they fit snugly together. The spaces between cells are called intercellular spaces... The intercellular spaces are filled with air. The cells of the pulp are green, because their cytoplasm contains green plastids - chloroplasts. The color of chloroplasts is explained by the presence of chlorophyll, a green green pigment. Chlorophyll in chloroplasts is formed only in the light. Chloroplasts of flowering plants are sometimes called chlorophyll grains because of their shape.
When viewed under a microscope internal structure leaf blade, in it you can see cut across veins... They contain transverse sections of cells - vessels, sieve tubes and fibers. Thus, the veins are conductive beams sheet. Strongly elongated cells with thick walls - fiber- give strength to the sheet. Water and minerals dissolved in it move through the vessels. Sieve tubes, unlike vessels, are formed by living long cells. Cross baffles between them are pierced by narrow channels and look like sieves. Solutions of organic substances move along the sieve tubes from the leaves.
Plants capture light mainly in leaf blades. In some plants with short stems, the leaves are collected in rosettes, and sunlight hits each leaf. The leaf petioles of many plants are capable of bending, turning the blade towards the light. This makes it possible to better absorb the sun's rays. For example, in ivy, the leaves always face the light, and if the plant is turned, after a while the leaf blades will also turn to the light and arrange themselves in the form of a leaf mosaic, almost without shading each other.
Water evaporates from the surface of the sheet. Inside the leaf, water vapor passes through the intercellular spaces to the stomata and evaporates mainly through them. Young leaves especially evaporate a lot of water. Different plants vaporize different amount water. Evaporation depends on environmental and stomatal conditions. If the plants have enough water, the stomata are open day and night. In some plants, the stomata are open only during the day and close at night. Thus, evaporation is regulated by the opening and closing of the stomata.
Plants of tropical rainforests - ficuses, begonias, philodendron - have large leaves that evaporate a lot of moisture. Appearance Dryland plants are also distinctive. The leaves of these plants are small. Sometimes, like cacti, they are replaced by thorns. The leaves of many plants in dry places are adapted to reduce evaporation. This is a dense pubescence, a waxy coating, a relatively small number of stomata, and other adaptations. For example, aloe, agave leaves are fleshy and juicy. They store water.
Leaves can also be modified because they play some other role that is not characteristic of typical leaves. For example, in barberry, some leaves turn into thorns. They evaporate less moisture and protect the plant from being eaten by animals. In peas, the tops of the leaves are turned into tendrils. They serve to keep the stem of the plant upright.
Interesting leaves carnivorous plants... A small sundew plant grows in peat bogs. Sundew leaves are covered with hairs that secrete a sticky liquid. Glittering like dew, sticky droplets attract insects. On a leaf, insects become bogged down in a sticky liquid. First, the hairs, and then the leaf blade, bend over and cover the victim. When the plate and hairs unfold again, only its integument will remain of the insect. The leaf will digest and absorb all living tissues of the insect.
In autumn, the leaves gradually turn yellow and turn red due to the destruction of chlorophyll. By autumn, the cells of the leaves accumulate substances that are unnecessary to plants, and sometimes harmful to them. Leaf fall begins. Leaf fall is also the adaptation of plants to reduce evaporation in autumn and winter.
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In botany, leaves are an integral part of the plant's stem system. The leaf of a tree consists of a leaf blade (a flattened part of a leaf), a petiole (stem) and stipules (appendages at the base of the leaf). The leaves on trees come in a variety of shapes and sizes. The entire crown of a tree must occupy a sufficiently large surface area of the tree, this is important for the absorption of light by chlorophyll during photosynthesis and carbon dioxide (CO2) for the production of organic molecules.
Such different leaves
Typically, a tree leaf consists of a wide blade (blade) attached to the stem. Leaves vary in size, shape, and some other characteristics, including the type of venation (location of veins). Different types venation is characteristic of different types Plants, for example, dicotyledons have a net venation; in monocotyledonous plants, leaf venation is parallel. Leaves can also be simple and compound.
The structure and function of the sheet
The leaves of trees have a number of important functions and also contain water, which is needed to convert light energy into glucose during photosynthesis. The leaves have two structures that minimize water loss - cuticle and stomata. The cuticle is a waxy bloom on the top and bottom of the leaves that prevents water from evaporating into the atmosphere.
The main function of the leaf is to produce food for the plant through photosynthesis. Chlorophyll, the substance that gives plants their characteristic green color, absorbs light energy. The inner part is protected by the epidermis. The central leaf, or mesophyll, consists of a soft wall; its cells are known as parenchyma. One fifth of the mesophyll consists of chlorophyll, which contains chloroplasts. They absorb sunlight to release oxygen and, in combination with certain enzymes, extract hydrogen from the water.
The oxygen released from the green leaves is used for the respiration of plants and animals. Hydrogen obtained from water, in combination with carbon dioxide, participates in the enzymatic processes of photosynthesis in the form of sugars, which are the basis of flora and fauna. Oxygen enters the atmosphere through special pores on the leaf surface.
Although the cuticle has an important function of protecting against excessive moisture loss, the leaves cannot be impenetrable because they must also allow carbon dioxide to be absorbed. After CO2 enters the leaf through the stomata, it moves to the mesophyll cells, where photosynthesis takes place, followed by glucose production.
What determines the color of the leaves?
Responsible for color are chlorophylls, green pigments that are usually present in much more, than others. In the fall, chlorophyll production slows down as the days get shorter and cooler. Chlorophyll gradually breaks down and disappears, and the colors of other pigments begin to appear. These include carotene (yellow), xanthophyll (pale yellow), anthocyanin (red, blue-violet), and betacyanin (red). Tannins, for example, give oak leaves their dark brown hue.
Leaf life
The tree leaf is basically a short-lived structure. Even when they last for two or three years, for example, conifers and broadleaf evergreens, after the first year they do not benefit the whole tree as much as in the beginning. Leaves begin to fall off at the base of the leaf petiole. This usually occurs in the fall, although other factors can influence this natural biological process, such as abscission due to insect damage, disease or drought.
Closer to autumn, the leaf of the tree undergoes some age-related changes, as the days are getting shorter and there is less sunshine. As a result, the petiole zone begins to soften until the leaf falls off. A healing layer forms on the stem, which tightens the wound, leaving a kind of scar.
Components of the sheet
The main leaf of angiosperms consists of the base of the leaves, stipules, petiole, and blade (plate). The base of the leaves is slightly widened where the leaf attaches to the stem. Paired stipules, if present, are found on each side of the base leaf and resemble scales, spines, or leaf-like structures. The petiole is the stem that connects the blade to the base of the leaves. The blade is the main photosynthetic surface of the plant.
Types and forms of leaves
The shape of the leaves of trees can be different. Simple and complex leaves can be found in nature. When only one blade is connected to the petiole, then the leaf is called simple, it can also, in turn, be cut along the edges of the most different ways... Such leaves can be whole and even, and they can also have jagged or serrated fields. Also, the edges can be rounded or scalloped. A wide variety is found at the top and bottom of the leaf. There are leaves that do not have a petiole and they attach directly to the stem, and some leaves may not have stipules.
By the type of arrangement, the types of leaves of trees can be distinguished as follows: alternate, paired (opposite) and whorled. With the next arrangement, the leaves are evenly distributed over the stem, alternately forming an ascending spiral. In a paired arrangement, the leaves of the plant are opposite each other. The plant has a whorled type of arrangement, when three or more leaves emanate from one node.
Needles are also leaves
The shape of the leaves is the main tool for identifying plant species. Conifers such as spruce, fir, and pine that grow in cold conditions have needle-shaped leaves. The needle-shaped leaves help in reducing water loss. In hot climates, plants like cacti have succulent leaves, which also help conserve water. Many aquatic plants have leaves with a wide blade floating on the surface of the water, while the thick waxy cuticle on the surface of the leaves repels water.
With regard to the distribution of plants on Earth, climate is a determining factor, which is why vegetation zones almost always correspond to climatic zones... From the characteristics of the climate and environment the variety of species and forms of vegetation fully depends. Leaves, which are primarily photosynthetic organs, also adapt to climatic conditions in the most optimal way.
People write poems and songs about them, admire them in spring, summer and autumn, look forward to their appearance in winter. They are a symbol of life and the rebirth of nature, a delicate dress that pleases the eye and gives pure oxygen to all living things on earth. These are leaves - what we see every day and what no plant, and indeed our entire planet, can live without.
- The yellow leaves are circling over the city, with a quiet rustle they fall under our feet ...
- Maple Leaf, Maple Leaf, dream about you in the middle of winter ...
- Green leaves ringing to all those who were in love ...
What are leaves, why are they needed, why they turn yellow in autumn and grow again in winter, what color and shape they are - you will learn all this and much more from this publication.
Functions of leaves, their role in the life of plants
Speaking dry scientific language, the leaf is one of the most important plant organs, the main function of which is to participate in the process of photosynthesis.
[!] Photosynthesis - transformation solar energy v organic compounds inside the plant. Simply put, through photosynthesis, plants get their food from the sun's rays.
In addition, with the help of the leaves, the plant breathes and evaporates moisture (gives off dew).
As you can see, plant life would be impossible without green covers, but not only plants depend on leaves. With the help of these peculiar lungs, the plant neutralizes carbon dioxide and releases oxygen, which is necessary for people, animals, and insects, that is, for all life on the planet.
In general, the sheet consists of several parts:
- Base - the place of attachment to the stem;
- Stipule - leaf-like elements at the base, in some cases fall off after the leaf is fully opened;
- Petiole - continuation of the main vein of the leaf plate, connecting the leaf and the stem;
- A sheet plate is a wide part of a sheet that performs its main functions.
Since each plant is individual, and the leaves are very different, some parts may not be there. For example, stipules are often absent, sometimes there is no petiole (in this case, the leaves are called sessile or pierced). In addition, all parts can be of various shapes, length and structure.
The classification and separation of the main parts helps botanists to correctly identify the plant and determine which family, genus and order it belongs to.
The structure, types and forms of the sheet plate
The lamina consists of the upper epidermis covered with cuticle, the palisade layer, the spongy layer, and the lower epidermis also covered with the cuticle. Each of the layers has a specific function:
- The cuticle and epidermis protect the plate from external influences, prevent excessive evaporation of water.
[!] The stomata are responsible for the process of retaining the necessary moisture inside the leaf - paired cells that can close and prevent moisture from evaporating. The stomata begin their work in drought, saving the plant from dehydration.
- The palisade layer, also called the columnar tissue, is responsible for the process of photosynthesis. Chloroplasts are also collected here, cells staining the leaf surface green.
- Spongy tissue is the basis of a sheet plate. Its functions are gas exchange, carbon dioxide absorption and oxygen evolution, and photosynthesis.
The entire plate is permeated with conductive bundles, called veins, through which organic matter is delivered from the root to the leaf (water and minerals) and vice versa (sugar solution). In addition, the veins form a solid skeleton that protects soft tissue from breaks.
Plate shapes
In general, all forms of leaves are divided into simple and complex, and complex ones into finger, pinnate, two-pinnate, three-leafed, pinnate, which, in turn, are divided into several more types. In total, botany has at least thirty-five varieties of forms.
Simple leaves consist of one leaf plate, while it can be the most different shapes: round, oval, diamond-shaped, elongated and so on. The shape of the tip of the plate and the place of attachment of the petiole also differ.
Complex leaves are those that consist of several parts, both articulated on a common petiole (lobed, dissected, separate), and having their own separate petiole (finger, pinnate, three-leafed).
[!] One of the signs of complex leaves is their fall at different times.
In addition to the general configuration of the leaf, its base (round, cordate, treelike, unequal, etc.) and apex (pointed, notched, antennae, obtuse, etc.) are distinguished.
Edge shapes
The edge of the sheet, as well as its general form, tells botanists that the plant belongs to one or another species. Depending on the depth of the dissection, the edges are divided into finger or toothed (shallow grooves), lobed, dissected, and separate (deep grooves). Smooth edges are called all-edge.
Types of venation
The venation pattern of the leaf plate can be very diverse and depends on the type of plant. In general, all types of venation are divided into two parts:
- several parallel veins pass through the leaf plate, while the central vein is absent (parallel venation),
- there is a main (central) vein, from which lateral (reticular) veins branch off,
- several curved veins diverging in the middle of the leaf and converging to the edge (arcuate venation).
In turn, the reticular venation is divided into several subspecies.
Types of stipules and petioles
The stipule usually looks like a small, underdeveloped leaf located at the base of the leaf. They may fall off after the leaf is fully opened, or remain on the plant. Depending on the method of attachment to the petiole, stipules are loose, fused with the petiole, interstitial, bell-shaped or encircling the base of the petiole.
The petioles can differ in the shape of the cut: a cylinder, a half-cylinder, with a recess, and others. In addition, as mentioned above, the petiole may not be at all; in this case, the leaf is attached directly to the stem.
As you can see vegetable world demonstrates an amazing variety of forms, while there are millions of their combinations.
So, the scientific and botanical part is over, it's time to move on to amazing facts about the leaves.
How Plants Adapt to Climate and Other Habitats Using Leaves
Each plant is forced to acclimatize to weather conditions, as well as to protect itself from external influences. All parts of the plant: roots, shoots, flowers and, of course, leaves, have adapted to various climatic phenomena: high or low temperatures, drought or excessive moisture, lack or excess of sunlight. In addition, plants are threatened by humans and animals, so many of them have learned to repel attacks in the process of evolution.
Consider how a plant resists an unfavorable environment with its green cover.
Arid or humid climates:
- The small size of the leaves and, accordingly, the small area of the leaf plate prevents excessive evaporation of water;
- Leaves are usually thick, juicy - thus the necessary moisture accumulates in them;
- The leaf plates of many plants are covered with hairs, which also prevents evaporation;
- A smooth waxy coating on the surface serves the same purpose.
- Large leaves are a sign of tropical plants, due to big size the plate evaporation process is much more intense.
Crassula, saintpaulia, philodendron Windy areas:
- The split, jagged shape of the edge allows air currents to pass freely, thanks to which gusts of wind do not injure the leaf.
Hanging birch "Dalecarlian", monstera, finger maple Locations with excessive or insufficient sunlight:
- If there is not enough sunlight, many plants can unfold their leaves in such a way that as much sunlight as possible hits their surface;
- Leaf mosaic is a phenomenon in which smaller leaves are located between larger cousins. In this case, each leaf captures the sun's rays and participates in the process of photosynthesis;
- Some plants that do not need a large number sun, filter light through special translucent windows located on the leaves.
Dandelion, ivy, fenestraria Aquatic plants- these representatives of the flora stand apart, because in order to survive, they had to adapt not even to the climate, but to a completely different element - water:
- The leaves of hydatophytes (plants completely submerged in water) are highly dissected. Thus, by increasing the surface area, the plant gains required amount oxygen;
- Leaves floating on the surface of the reservoir do not have stomata on the back of the leaf plate;
- The large surface area of floating leaves prevents them from sinking due to the distribution of the load.
- Special microscopic projections and a wax layer prevent water from penetrating into the leaf, excluding plant infection with microorganisms and protozoa. Water is not absorbed into the surface, but drips down the leaf in drops, at the same time clearing it of dust and dirt. This phenomenon is called the "lotus effect".
Hornwort, victoria amazon, lotus Protection from animals and people. Some plants in the course of evolution have learned to defend themselves against encroachments:
- The leaves produce strong-smelling pheromones and oils that repel animals;
- The leaf blade is sometimes covered with soft hairs or even hard spines that sting the aggressor.
Geranium, nettle, woolly chisel Fancy leaves
Nature has endowed certain plant species with such an extravagant appearance that sometimes it is difficult to determine where the leaves are in front of us.
Cactus have settled in areas with arid climates, where the loss of every drop of water is tantamount to death. Evolutionary selection did its job - specimens with a minimal evaporation area survived. Wide leaves are an unaffordable luxury for such conditions of existence. All external decoration of cacti, inhabitants of arid wastelands, are compact protective thorn leaves.
Opuntia, Trichocerius, Schlumbergera Other plants in arid regions, so as not to evaporate precious moisture, have decided to completely abandon the leaves. Rather, they still have leaves, but only in the form of small undeveloped scales. At the same time, shoots called cladodia or phyllocadia acquired the shape of the leaf and the function of photosynthesis. Fillocadia have adapted to the new role so much that they practically do not differ from an ordinary leaf, but in fact they are not.
There is also the opposite option - what seems to be shoots are actually leaves. One example is the tendrils of creeping plants. In this case, the antennae are the upper parts of the leaves that have adapted to cling to the support.
Butchery, asparagus, pickling peas Some of their most unusual leaves belong to tropical exotics. The hot, humid climate, the abundance of insects and animals forced the plants to adapt to the difficult conditions of existence and even go into the category of predators. With sticky secretions or special bubbles on the leaves, carnivorous plants catch gape insects, and then suck life juices out of them.
Another gimmick tropical plants- a bag formed by the intergrown planes of the sheet plate. Going into this trap rainwater, the stock of which, if necessary, is consumed during periods of drought.
Dewdrop, pemphigus, Rafflesa dyschidia Leaves of different colors
What color are the leaves? At first glance, the answer to this question is very simple - green in summer, yellow and red in autumn. In fact, they can be the most different colors not only in autumn, but also at other times of the year. You can find green, yellow, red, silvery burgundy and even purple shades of color of the natural decoration of completely healthy plants. In addition to unusual pigmentation, the leaves of some, especially southern, plants have beautiful patterns and ornaments.
Zebrina, fittonia, caladium
Leaves are not only pleasing to the eye and necessary for the life of the planet, some of the leaves are also edible and, moreover, make up a considerable part of the human diet. In cooking, they are also used as a vegetable component: spinach, Swiss chard, Peking cabbage, Chinese cabbage, and as salad ingredients: rucola, sorrel, lettuce, and, of course, as seasonings: dill, parsley, basil, mint, and so on.
Chinese cabbage, lettuce, basil Answers on questions
At the end of the article - answers to the most popular questions about leaves.
Why is the sheet flat?
This shape increases the area of the leaf plate, and, in turn, the large surface area increases the number of cells involved in the process of photosynthesis.
What determines the size of the sheet?
The size and, accordingly, the surface area of the leaf depends on the habitat of the plant. The leaves of plants from dry areas are usually small, while those from wet areas are large. The point is that what larger area leaf, the more stomata are on its surface and the more intensive is the evaporation of water. Where there is often drought, in order to survive, plants try not to evaporate a lot of moisture, and in a tropical climate, the evaporation process, on the contrary, should be as intense as possible.
Why are the leaves green?
Chlorophyll is responsible for the green color of the leaf, which is involved in the conversion of carbon dioxide into nutrients... The high content of chlorophyll in the lamina gives plants a fresh green hue.
[!] Chlorophyll of some plants is colored in other colors - red, brown, violet, so the leaves of such plants have corresponding shades.
Why do the leaves turn yellow?
In autumn, the chlorophyll in the leaves is destroyed, it becomes less. Due to the decrease in chlorophyll, the intensity of the green spectrum also gradually decreases. In the foreground are the yellow and red pigments (xanthophyll, carotene, anthocyanin) contained in the leaf cells.
[!] Leaves of individual plants do not change color and fall off green.
Why do leaves fall in autumn?
Seasonal changes in daylight hours and average daily temperatures, forced the plants to adapt to the changing conditions of existence. By the onset of winter cold most of flora sheds summer decoration and goes into a state of suspended animation, commonly called winter hibernation. Exchange processes in life systems the plants practically stop. Leaves, so necessary in the summer to evaporate excess moisture and collect life-giving sunlight, become simply unnecessary and fall off.
During spring and summer, leaves extract and process nutrients necessary for plant life. In the process of such processing, green lungs of nature produce and accumulate metabolites - excess mineral salts, thus playing the role of a kind of filter. Over time, the deposits become more and more and in the fall the plant gets rid of the leaf, which is no longer useful.
This is the way it is in nature, nothing is wasted. Fallen leaves shelter the ground from frost, protecting the soil. In the warm season, the carpet covering the soil gradually decomposes, overheats. Insects, bacteria and microorganisms process the formed humus into a nutritious soil for living plants, closing the cycle in nature.
The leaf is the most important organ of a plant, its main function is photosynthesis, that is, the synthesis of organic substances from inorganic ones. However, according to the external structure, the leaves of plants of different types are different. By the shape of the leaf, you can often determine which plant species it belongs to. The variety of external structure of leaves is mainly due to the fact that plants are adapted to different conditions life.
Plant leaves vary in size. The smallest leaves are less than a centimeter in size (wood lice, duckweed). Huge leaves are characteristic of some tropical plants. So have aquatic plant Victoria, the diameter of the leaves is more than a meter.
In external structure leaves of most plants secreteleaf blade and petiole... The leaf blade contains mainly photosynthetic tissue, and the petiole serves to connect the leaf blade with the stem. However, in some plant species, the leaves do not have petioles. Leaves with petioles typical for most trees (maple, linden, birch, etc.). Leaves without petioles characteristic of aloe, wheat, corn, etc.
With an external examination of the sheet, the so-called veins... They are best seen on the underside of the sheet. The veins are formed by conductive bundles and mechanical fibers. Water and mineral substances move along the conductive tissue from the roots, and in the opposite direction, from the leaves, organic substances. The mechanical fabric gives the leaves their strength and rigidity.
At parallel venation the veins in the leaf blade are parallel to each other and look like straight lines.
At arc venation the arrangement of the veins looks like a parallel one, but the farther from the central axis of the leaf blade, the more the vein has the shape of an arc, and not straight.
Parallel and arcuate venation is characteristic of many monocotyledonous plants. So many cereals (wheat, rye) and onions have parallel venation, and lily of the valley - arched.
At reticular venation the veins in the leaf form a branching network. This venation is typical for many dicotyledonous plants.
There are other types of leaf venation.
Simple and complex leaves
Depending on the number of leaf plates on one petiole, the leaves are divided into simple and complex.
Have simple leaves only one leaf blade develops on one petiole (birch, aspen, oak).
Have compound leaves several or many leaf plates grow from one common petiole; moreover, each such leaf has its own small petiole, which connects it with a common petiole. Examples of plants with complex leaves are mountain ash, acacia, strawberry.
Leaves arrangement
On the stem of the plant, nodes and internodes are distinguished. Leaves grow from the nodes, and internodes are the sections of the stem between the nodes. The arrangement of the leaves on the stem may vary depending on the type of plant.
If the leaves are arranged one at a time in the nodes, while all together the leaves give the appearance of an arrangement, as it were, in a spiral along the stem, then they speak of the next arrangement of leaves... This arrangement is typical for sunflower, birch, rose hips.
At opposite leaves grow two at each node, opposite each other. The opposite arrangement is found in maple, nettle, etc.
If more than two leaves grow in each node, then they speak of whorled leaf arrangement... It is typical, for example, for elodea.
There is also rosette arrangement of leaves, when there are almost no internodes, and all the leaves grow, as it were, from one place in a circle.