Plant shoots are striking in their diversity and originality. But environmental conditions often require new adaptations from representatives of this kingdom. Modified shoots are able to perform additional functions. Thus, they provide a higher viability of organisms.
Modifications of underground shoots
These metamorphoses can be above ground or underground. Modified underground shoots are the most common and widely represented in nature.
One of them is the rhizome. By its name and appearance, it resembles a root. But, unlike the underground organ, it consists of elongated internodes and nodes. On the stem of the rhizome there are accessory buds, from which, with the onset of favorable conditions, leaves grow. In the nodes are also accessory roots. An elongated horizontal stem is located underground, where temperature differences and drought have less effect on the life of the plant. And the supply of water and nutrients significantly increases the chances of the plant organism to survive.
Many were faced with a situation when you need to get rid of annoying wheatgrass, overgrown lilies of the valley or other plants that have rhizomes. This is not so easy. Modified shoots grow greatly, their parts often remain in the ground, forming new shoots. But, on the other hand, this ability is often used for the vegetative propagation of plants.
Tuber
A tuber is a modified shoot that is also located underground and stores nutrients. Everyone knows potato tubers of important economic importance. They accumulate a large amount of starch.
Some mistakenly consider this altered shoot to be a fruit. In fact, the fruits of potatoes are formed on aboveground shoots after flowering. The tuber is a thickened stalk with apical and lateral buds - eyes. Sprouting, the eyes form young shoots.
Elongated elongated and short-lived shoots are also called stolons.
Plants such as saffron and gladiolus have a corm - a thickened stem with subordinate roots. A layer of dead leaves protects the inner contents of the corm.
Bulb
Onions, garlic, tulip and lily have another modification - the bulb. On the flat stem, which is called the bottom, are the kidneys. Of these, several species of scaly leaves develop. Some of them are thick and fleshy. They store water with nutrients, providing life to the plant. Dry membranous leaves protect them from above. From sleeping buds on the bottom, young onion leaves, the so-called green onions, grow. Bulbs are also characteristic of plants in the steppe natural zone. In the conditions of cold, little snowy winters and hot, dry summers, this modification makes it possible for a plant underground to survive an unfavorable period in this form.
Overhead modifications of shoots
Modified shoots of plants can also be located above the ground. So, on the branches of hawthorn and thorns there are thorns - shortened and lignified modified shoots. They are the result of branching and sharpening of the stem, reliably protecting their owners from eating animals. Plants with thorns have tasty, juicy fruits with bright colors, so they need additional protection.
Strawberries and strawberries have an additional adaptation for vegetative propagation - elongated shoots of mustache. They are fixed in the soil, forming a new plant.
Mustache should not be confused with the mustache of grapes. They have a completely different functionality. With the help of antennae, the plant is attached to the support, occupying the most advantageous position in relation to the sun. This adaptation is also characteristic of pumpkins, cucumbers, watermelons.
Modifications of shoots in the direction of growth
Depending on the growing conditions, the shoots can also be modified. In woody and herbaceous plants, erect stems directed towards the sun are most often found. Creeping and creeping stems grow very quickly, cover the surface of the soil with shoots with leaves. This provides them with a prosperous life. Plants with climbing stems are called vines. They are characteristic of tropical and humid equatorial forests, although they are often found in temperate zones. For attachment to the support, creepers use special devices: hooks, trailers, bristles.
The internal structure of the modifications of the escape
Despite the external differences, various modifications retain all the features of the internal structure. For example, a potato tuber, being a thickened stalk, is covered with bark on top. It is we who clean it when we peel potatoes. On the longitudinal section of the tuber, a dark strip is clearly visible - wood. And in the core, friable main tissue, reserve nutrients are actively deposited.
If potato tubers are left in the light for a long time, they will begin to turn green. This indicates that the colorless plastids of the leukoplasts, in which starch accumulates, in the light turn into green chloroplasts. Such a product should not be eaten, because it contains a toxic alkaline alkaline solanin, which causes poisoning.
Modified shoot functions
It is the modified shoots that determine the survival of plants in adverse conditions. Storing valuable nutrients, they allow plants to survive during a drought. Biennials and perennials survive only due to the presence of bulbs and rhizomes. Their leaves, which appear on the surface in spring and develop all summer, die off with the onset of cold autumn. And the underground part lives, eating reserves of thickened stems. With the onset of heat, the plant resumes growth again.
Many modifications of the shoot are used for vegetative propagation, quickly enough increasing the number of valuable plants. This property is actively used by people in agriculture.
Origin of flower
A flower is a modified shoot. To prove this fact is very simple. It develops from a specialized generative kidney. This part of the shoot acquires characteristic features to perform the most important additional function - the implementation of sexual reproduction of plants. For this, you need a flower. The modified shoot is significantly shortened compared to ordinary stems. Its main parts are the stamen and pistil, in which the germ cells are located - sperm and egg, respectively. Bright color of the flower petals is needed to attract pollinating insects. Small flowers are collected in groups - inflorescences. So they are much more noticeable, and their aroma spreads more.
After pollination and fertilization, a fetus is formed in place of the flower. It consists of seeds and pericarp. The seeds give rise to a new plant, and the pericarp feeds and warms them.
In addition, a flower is a modified escape that for many centuries has been delivering aesthetic pleasure to people, inspiring poets and musicians.
Modified shoots are one of the main adaptations of higher plants to environmental conditions. In the process of evolution, they appeared to increase the viability of plant organisms in connection with the need for new functions in constantly changing living conditions.