Autumn is one of the most beautiful seasons. The variety and richness of nature during this period simply amaze the mind, the leaves are so simple and complex that they are so different. The leaf arrangement of each plant is special (it is alternate or whorled), and it is from this plant that it can be determined to which species it belongs. Let's take a closer look at the features and functions of each leaf type.
Definition in botany
Along with flowers, roots, stems and shoots, the leaves are the most important vegetative organs in plants, which are also responsible for the function of photosynthesis. In addition, they perform many other works, for example, participate in the processes of respiration, evaporation and guttation of plants. Distinguish the following types of leaves: simple and complex, each of them has its own characteristics and occurs in a particular plant species.
Very often, leaf blades are taken for leaves, but in fact it is an organ that consists of a plate (veins pass through it) and a stem that originates at the base and connects the leaf blade to the stipules. It always takes a lateral position on the stem, and all the leaves are located on it in a certain sequence in such a way as to provide optimal access to the sun's rays. Its size can vary from 2 cm to 20 m (in tropical palm trees).
External structure and forms
One of the features of these organs is their flat form, which ensures maximum contact of the surface of the plant with the air medium and sun rays. The forms of simple and complex leaves differ from each other in appearance. At simple there is only one leaf plate, which is connected with the base by means of petiole. Complex ones consist of several leaf blades located on one petiole. Remember how the maple leaf looks : in the middle is the thickest vein, to which are attached two or three stipules on each side. Such a complex shape of the sheet is called opposite, because the leaf blades are arranged symmetrically to each other.
The main components are the plates and veins that run along their surface, as well as the petiole, stipules (although they do not occur in all plants) and the base by which the element connects to the stem of a tree or other plant.
Unlike the shape of a simple sheet, complex ones can be found in several varieties that have their own distinctive features and characteristics.
The upper surface of the leaf blades is always covered with the skin, which consists of a layer of colorless cells of the integumentary tissue, the epidermis. The main functions of the skin are protection against external mechanical damage and heat exchange. Due to the fact that its cells are transparent, the sunlight passes through it unhindered.
The lower surface also consists of these transparent cells, closely adjacent to each other. However, among them there are small green-colored paired cells, between which there is a gap. It is this part that is called the stomata. Unfolding and reconnecting, the green cells open and close the entrance to the stomata. During these movements, moisture evaporates and the gas exchange process takes place. It is known that 90 to 300 stomata per 1 mm 2 fall on the surface of one sheet plate.
An interesting fact: green cells are almost always located on the side of the sheet on which the maximum air exchange takes place. So, for example, in floating on water plants, capsules or water lilies, the stomata are on the outer side facing the air.
Scientists distinguish two main types of leaves: this leaf is simple and complex. The structure of each of them has its own characteristics. Depending on the appearance, the number of plates and the shape of their edges, complex leaves can also be divided into several types. So, here are the most common species, if selected according to external signs:
- Fan-shaped (the shape resembles a semicircle);
- Spear-shaped (sharp, sometimes there are spines on the surface);
- Lanceolate (rather wide, with narrow margins);
- Oval (egg-shaped, which is slightly tapered closer to the base);
- Lobed and lobed (they can sometimes be confused, since they both have several blades);
- Thumb (the plates diverge from the petiole, the appearance looks like fingers);
- Needle (thin and rather sharp).
This list can be continued for a long time, however, the complex shape of the sheet has several more types depending on the shape of the edges, as well as the arrangement of the leaf blades themselves.
Types of Complex Plants
On the edges of the plates very often it is possible to determine to which species this or that plant belongs. The following forms are found most often in nature:
- All-edged - have smooth edges, on which there are no teeth completely;
- Jagged - as is clear from the name, such leaves have denticles along the edges;
- Finely toothed - they resemble a saw with very sharp and small incisors;
- Wavy - they have undulating cutouts that do not have strict order or standard shape.
Features of each type
It is worthwhile to talk in more detail about the distinctive features of simple and complex leaves, as this can help to determine what kind of plant it is and what kind of plant it belongs to. So, one of the most noticeable features of each kind is the number of records. If there are three elements, then we have triple-shaped sheets. If five - palpate, and if more, they are called pinnately divided. On each plate, you can observe a special system of venation, through which nutrients enter the internal tissues. In simple and complex species, they differ in shape and structure. Here are the most common types of veins:
- Arcuate (when venation resembles the shape of a menorah - one of the symbols of Judaism);
Another distinctive feature is how the leaves are arranged on the stem. Simple and complex - all without exception are attached to the stems of plants in two ways:
- With the help of a handle, in this case the plant belongs to the petiolate;
- Without a handle, when the base grows and covers the stem, then in front of us is a sedentary plant.
Plant leaves: simple and complex
If the plants are classified according to the characteristics of the leaves, the following facts can be noted. Simple are common in all herbaceous plants, including shrubs and trees. Complex ones are found both in shrubs and in trees, however, unlike simple ones, during leaf fall, they fall not completely at once, but in parts: first the plates themselves, and then the stalk.
Let's look at examples of simple and complex leaves in plants. Most of the trees that grow in Russia, the leaves are a simple species. Aspen, birch and poplar have different forms: lanceolate, rounded with jagged edges and spear-shaped, respectively. With the onset of autumn cold weather, each of them leaves the whole. They are also found in fruit trees such as apple, pear and cherry; Agricultural crops, such as oats and corn, also have simple leaves.
Complex forms are present on legumes, for example, pinnatulous leaves in peas. Leaves of palm-shaped form have the following trees: maple, chestnut, lupine, etc. Remember clover meadow, its shape is called troyatosyllabic with ciliary margins.
What are the functions of the leaves?
The simple and complex forms of these organs are largely conditioned by climatic conditions. In hot countries, trees have large leaves that serve as a kind of protective shield against sunlight.
However, the main irreplaceable function is participation in photosynthesis. As is known, it is through this process that trees can convert carbon dioxide to oxygen by absorbing solar energy.
The second most important process is cellular respiration. With the help of mitochondria, the leaves pick up oxygen, and through the stomata they exhale already carbon dioxide, which is then used during photosynthesis. Since photosynthesis occurs only by light, at night carbon dioxide is stored in the form of organic acids.
Transpiration is the evaporation of water from the surface of leaves. Due to this, the general temperature and humidity of the plant are regulated. The intensity of evaporation depends on the size and thickness of the plates and on the wind speed at a certain time.
Adaptation and modification
Many leaves - simple and complex - have the ability to adapt to environmental conditions. In the process of evolution, they acquired the ability to change. Here are the most amazing of them:
- Ability to produce wax, which falls on the surface and prevents the excessive evaporation of water droplets;
- Form storage for water during rains, it occurs due to the merging of the edges in such a way that a sack-shaped container is formed (such forms can be found in many tropical lianas);
- The ability to change the surface of the plates, rugged leaves prevent strong winds, thereby protecting plants from damage.
Many facts related to the vital functions of these irreplaceable plant organs are still poorly understood. These beautiful decorations of nature, in addition to the above functions, perform one more aesthetic task - they make people happy with their splendor and variety of bright colors!