Autumn is one of the most beautiful seasons. The diversity and richness of nature in this period simply amazes the mind, the leaves are so simple and complex. The leaf arrangement of each plant is special (it happens alternately or whorled), and it is from it that you can determine what species it belongs to. Let's take a closer look at the features and functions of each type of leaf.
Definition in Botany
Along with flowers, root, stem and shoots, 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 plant gutation. The following types of leaves are distinguished : simple and complex, each of them has its own characteristics and is found in a certain type of plant.
Very often, leaf blades are taken for leaves, but in fact it is an organ that consists of a leaf (veins pass along it) and a stem that originates at the base and connects the leaf blade with stipules. It always occupies 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 sunlight. Its sizes 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 shape, due to which the maximum contact of the plant surface with the air and sunlight is ensured. The shapes of simple and complex leaves differ in appearance. In simple cases, there is only one leaf blade, which connects to the base with the help of a petiole. Complex ones consist of several leaf blades located on one petiole. Remember what a maple leaf looks like : in the middle is the thickest vein, to which two or three stipules are attached on each side. Such a complex shape of the leaf is called opposite, because the leaf blades are arranged symmetrically to each other.
The main components are the plates and veins that pass along their surface, as well as the petiole, stipules (although not all plants have them) and the base with which the element connects to the stem of a tree or other plant.
In contrast to the shape of a simple sheet, complex ones can be found in several varieties that have their own distinctive properties and features.
Internal structure
The upper surface of leaf blades is always covered with a 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 transfer. Due to the fact that its cells are transparent, sunlight freely passes through it.
The lower surface also consists of these transparent cells that fit tightly together. However, among them there are small paired green cells, between which there is a gap. This part is called stomata. Opening and reconnecting, green cells open and close the entrance to the stomata. During these movements, evaporation of moisture and the gas exchange process occur. It is known that on the surface of one sheet plate accounts for from 90 to 300 stomata per 1 mm 2 .
An interesting fact: green cells are almost always located on the side of the leaf on which the maximum air exchange occurs. So, for example, in plants floating on the water, egg capsules or water lilies, stomata are on the outside facing the air.
Varieties
Scientists distinguish two main types of leaves: this is a simple and complex leaf. 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 types, if selected by external signs:
- fan-shaped (the shape resembles a semicircle);
- spear-shaped (acute, sometimes spines are present on the surface);
- lanceolate (quite wide, with narrowed edges);
- oval (ovoid, which is slightly sharpened closer to the base);
- cuneiform and lobed (they can sometimes be confused, since they both have several blades);
- palmate (plates diverge from the petiole, the appearance resembles 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 location of the leaf blades themselves.
Types of Complex Plants
At the edges of the plates it is very often possible to determine what species a particular plant belongs to. The following forms are most commonly found in nature:
- whole-edge - have smooth edges on which the teeth are completely absent;
- dentate - as the name implies, such leaves have denticles along the edges;
- fine-toothed - these resemble a saw, which has very sharp and small incisors;
- wavy - such have wavy cutouts that do not have a strict order or standard shape.
Features of each kind
It is worth talking in more detail about the distinguishing features of simple and complex leaves, as this can help determine what kind of plant it is and what kind it belongs to. So, one of the most noticeable features of each species is the number of plates. If there are three elements, then we have triple-shaped sheets. If five are palmate, and if more, then they are called cirrus divided. On each plate, a special venation system can be observed, due to which nutrients enter the internal tissues. In simple and complex varieties, they vary in shape and structure. Here are the most common types of vein arrangement:
- arcuate (when venation resembles a menorah in form - one of the symbols of Judaism);
- transverse;
- longitudinal;
- palmate;
- parallel;
- mesh;
- cirrus.
Another distinguishing 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 is petiole;
- without the handle, when the base grows and covers the stem, then we have a sitting plant.
Plant Leaves: Simple and Complex
If we classify plants according to the characteristics of leaves, then the following facts can be noted. Simple are usually common in all herbaceous plants, including shrubs and trees. Complexes are found both in shrubs and trees, however, unlike simple ones, during leaf fall they do not fall all at once, but in parts: first the plates themselves, and then the stalk.
Let's look at examples of the name of simple and complex leaves in plants. In most trees growing in Russia, the leaves are of a simple form. Aspen, birch and poplar have different shapes: lanceolate, rounded with serrated edges and spear-shaped, respectively. With the onset of autumn cold weather, each of them leaves completely crumble. They are also found in fruit trees such as apple, pear and cherry; Crops such as oats and corn also have simple leaves.
Complex forms are present on legumes, such as cirrus leaves in peas. The leaves of a palmate shape have the following trees: maple, chestnut, lupine, etc. Remember the meadow clover, its shape is called ternary with ciliary edges.
What are the functions of leaves?
The simple and complex forms of these organs are largely due to climatic conditions. In hot countries, trees have large leaves, which serve as a kind of protective fence from sunlight.
However, the main indispensable function is participation in photosynthesis. As you know, it is thanks to this process that trees can convert carbon dioxide into oxygen by absorbing solar energy.
The second most important process is cellular respiration. With the help of mitochondria, the leaves accumulate oxygen, and carbon dioxide is already exhaled through the stomata, which is then used during photosynthesis. Since photosynthesis occurs only in daylight, carbon dioxide is stored in the form of organic acids at night.
Transpiration is the evaporation of water from the surface of leaves. Thanks to this, the general temperature and humidity of the plant is regulated. The evaporation rate depends on the size and thickness of the plates and on the wind speed at a certain point in 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:
- the ability to produce wax, which lays on the surface and prevents the excessive evaporation of water droplets;
- form storages for water during rains, this is due to the fusion of the edges in such a way that a bag-like capacity forms (such forms can be found in many tropical vines);
- the ability to change the surface of the plates, rugged leaves impede the effects of strong winds, thereby protecting plants from damage.
Many facts related to the vital activity of these irreplaceable plant organs are still poorly understood. These beautiful jewelry of nature itself, in addition to the above functions, perform another aesthetic task - they delight people with their splendor and a variety of bright colors!