Escape is the aerial part of any plant. It consists of the axial part - the stem, and the side - the leaf. It is the stem that performs the functions of locating the body in space and transporting substances. What structural features allow this body to ensure plant viability?
What is a stalk?
The stem is the axis of the shoot, its central and main part. In the process of evolution, it arose as a factor in the adaptation of plants to the terrestrial habitat. Thanks to the appearance of mechanical tissues, plant organisms were able to settle vertically in space. The developed system of conductive tissues led to the process of continuous flow of water from the soil and organic substances from photosynthetic organs.
Stem functions
But the stem is not only an organ that is the axial skeleton of plants and provides an upward and downward flow of essential nutrients. For example, in higher spore plants, horsetail, it is chlorophyll-bearing. And cacti significantly increases in size, storing water. The process of photosynthesis is also carried out by this organ, since the leaves of this plant turned into needles in order to lose less moisture.
On each stem are not only leaves, but also buds. These are future organs that are in their infancy. They are vegetative and generative. The first give rise to the vegetative organs of plants - leaves and shoots. The second contains the rudiments of the generative organ that provides sexual reproduction, the flower.
The external structure of the stem
On the stem with a naked eye it is easy to notice the places of attachment of leaves or scars that they left. They are called nodes. And the distances between them are internodes. The stem and leaf blade form an angle - the sinus of the leaf. It has axillary (lateral) kidneys. Due to them, the escape branches. Growth in height is provided by the apical buds of the plant.
In nature, frequent modifications of the stem. They contain the same structural elements, but visually look different. For example, the peppermint rhizome has rather elongated internodes and, being underground, keeps the plant viable longer.
Internal structure
The functions of the stem are determined by the features of its internal structure. Outside the organ is covered with cells of the integumentary tissue. They can be alive (peel) or dead (cork). They protect the contents of the stem from mechanical damage.
The peel exists in young plants whose age does not exceed one year. It contains special structures - stomata, due to which gas exchange occurs.
Later, this living tissue is replaced by a multilayer cork, and the stomata are replaced by small lentil tubercles. As the plant grows, its thickness also increases. It provides a protective function more effectively, since its dead cells are empty, only air is in them. Tightly adjacent to each other, they create a serious barrier to negative environmental factors: dangerous microorganisms, dust. excessive transpiration.
The next layer is represented by bark. It consists of sieve cells and satellite cells, providing movement and storage of substances. In the same layer are bast fibers - elements of mechanical tissue that make the stem strong. It is thanks to them that during strongest hurricanes, tree trunks remain safe and sound.
Next is the lateral educational tissue of the stem - cambium, due to which the stem grows in thickness, sometimes reaching significant sizes. Their work is especially intensified in the spring and summer.
The largest part of the stem is wood. The conductive elements of this part transport substances, mechanical ones provide strength, and the main ones store the necessary substances. This layer is the widest, densest and most valuable for human use in its economic activities.
In the center is the core, the large and loose cells of which perform a storage function.
Diversity
The shape of the axis of the shoot and its location in space can be very diverse. Most plants have erect stems. Well-developed mechanical tissues and the root system, which firmly holds the plant in the soil, allow them to reach the sun. Similar stems can lignify or remain grassy.
Creeping and clinging stems allow their owners to quickly develop new territories, crowding out other plants. They have special devices for vegetative propagation, for example, strawberry mustache. But ivy with the help of special trailers can grow even on a vertical and rocky surface. A winding hop stem encircles any support, mastering a decent area for photosynthesis.
The shape of the stem of representatives of the plant world can vary. So, in cereals it is rounded, and in sedge - trihedral. Representatives of the Umbrella and Pumpkin families have a hollow stem.
What is a trunk?
There are several life forms of plants: grasses, shrubs and trees. The latter are distinguished by the presence of one well-developed stem. Intensive cell division of the lateral educational tissue - cambium - leads to a thickening of the axis of the shoot and the formation of the trunk.
Cambium cells divide annually, forming a layer of a certain thickness - annual rings. By their number, you can determine the age of the plant.
The best
In the photo below - the stem of the largest tree in the world - sequoias. The trunk of this representative of the plant world can reach a height of more than 80 m.
Sequoia General Sherman is also a long-liver. Presumably her age is about 2500 years.
Most of the water is stored in the baobab trunk. This tree is also the largest trunk in the world. But the stem of the orchid has a length of 0.5 mm, being the smallest.
Modifications
Depending on what functions the stem performs, it can acquire new structural features, forming modifications of the stem. These include potato tuber. It consists of a thickened stem with vegetative buds called eyes. By the way, tubers are not only underground, like the aforementioned potatoes and earthen pears - Jerusalem artichoke. Kohlrabi cabbage forms an elevated tuber rich in valuable minerals.
Modifications of the stem have wheatgrass, physalis and lily of the valley. They are called rhizomes. On their long internodes are the rudiments of leaves and buds, from which the adventitious roots and green leaves of shoots develop.
The stem is also the bulb of garlic, lily and tulip. Their flat and underdeveloped stem is called the bottom. The root system of such plants is fibrous, represented by a bunch of adventitious roots. From buds located at the bottom, leaves develop. They can be of several types. So, onions juicy and fleshy leaves protect dry and membranous. And when favorable conditions occur, a young green shoot grows from the buds.
Modifications also serve for the vegetative propagation of plants. An example of this is a strawberry mustache. The cucumber tendrils help this plant cling to the support, allowing it to occupy the most advantageous position in space in relation to the sun.
The remedies are thorns of thorns, wild pears, barberries and hawthorn. These trees are famous for juicy fruits with bright colors, which many animals love to regale. Sharp thorns do not allow them to do this, and the fruits remain ripen on the branches.
A stem is an organ that is critical to plant life. A man uses it in economic activities; he makes household items from wood. Many modifications of the shoot are eaten, serve for vegetative propagation, providing increased viability of many plants.