The organs of flowering plants, the most evolutionarily developed representatives of this kingdom of wildlife, have a fairly diverse structure and functions. The underground part of the plant is called the root, the aboveground part is called the shoot. It is the shoot of plants that performs the most important functions: gas exchange, photosynthesis, transpiration, vegetative reproduction and its optimal location in relation to the sun.
The origin of the escape
In the process of evolution, this organ appears in the first land-dwellers - rhinophytes. Its stems were creeping and forked, because the mechanical tissues were still poorly developed. But even with such a primitive structure, the photosynthetic surface increased, which means that the plant organism was better provided with carbohydrates.
What is plant shoot
Escape is called the aerial part of the plant, consisting of the stem and leaves. All of these organs are vegetative, providing growth, nutrition and asexual reproduction.
Escape of plants also contains rudimentary organs - kidneys. There are two types of kidneys: vegetative and generative. The first type consists of a rudimentary stem and leaf, on top of which there is an educational tissue (meristem), represented by a growth cone. If, in addition to the stem and leaves, the bud contains the beginnings of flowers or inflorescences, it is called generative. In appearance, such kidneys are distinguished by larger sizes and a rounded shape.
The place to which a leaf is attached on a stem is called a node, and the distance between nodes is an internode. The angle between the stem and the leaf is called the axil.
In the process of development, organs responsible for generative (sexual) reproduction appear on the shoot: flower, fruit and seed.
Development of shoot from the kidney
With the onset of favorable conditions in the spring, the meristem cells of the growth cone begin to actively divide. Shortened internodes increase in size, resulting in a young shoot of plants. At the very top of the stem are the apical buds. They provide the growth of the plant in length. Axillary and adnexal buds are located in the leaf axil or internode, respectively. Due to them, the stem forms side shoots, i.e. branches.
Methods of branching plants
Depending on the structure, there are several ways of branching shoots:
- Dichotomous. The most primitive type of branching, in which two grow from one point of growth, two from each of them, etc. This is how some algae and higher spore plants grow: club mosses and ferns.
- Primopodial. Such branching can be seen both in gymnosperms (pine, spruce) and angiosperms (oak, maple). For a long time the stem of these plants grew inlength, followed by the formation of lateral branching.
- Sympodial. With this method, apical growth, on the contrary, stops. And the lateral buds are actively growing, forming more and more lateral shoots. Pear, cherry and other flowering plants are typical examples of this type of growth.
Modifications of shoots
What is a plant shoot and how does it look, of course, everyone knows. But environmental conditions often require the appearance of additional functions. This is easily provided by the organs of flowering plants. The shoot is modified, acquiring new structural features, while it consists of parts of a standard shoot.
The main modifications of the escape include:
Rhizome - located underground, where it most often grows horizontally. It has elongated internodes and buds, from which leaves appear on the surface of the earth in a favorable period. Therefore, plants with rhizomes (lily of the valley, wheatgrass, valerian) are very difficult to get rid of. After tearing off the leaves, the shoot itself remains in the ground, growing more and more
- Tuber is a thickened internode with buds - eyes. The most prominent representative of plants that form tubers is potatoes. Since it grows in the ground, it is often confused with a modified root. However, there are also above-ground tubers, for example, kohlrabi.
- Bulb - a modified shoot of plants with well-developed leaves located on a flat stem - the bottom. Typical for garlic, onion, tulip, lily. In internal juicyleaves accumulate nutrients, and the outer dry ones protect them from damage.
- Thorns are a protective device of pear, sea buckthorn, hawthorn and other plants. Being in the axil of the leaf, they reliably protect the plant from animals that want to feast on them.
- Antennae are modified climbing shoots that fix plants in a certain position. Cucumber, grapes, pumpkin are the most common plants that use this device.
Mustache - thin shoots with long internodes. Strawberries and strawberries reproduce vegetatively with the help of whiskers
As you can see, the shoot of plants consists of parts that are functionally interconnected, can be modified depending on environmental conditions and give each plant its own unique look.
