The shoots of plants amaze with 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 a rhizome. Both in name and in appearance, it resembles a root. But, unlike the underground organ, it consists of elongated internodes and nodes. Adnexal buds are located on the stem of the rhizome, from which, with the onset of favorable conditions, leaves grow. The nodes also contain adventitious roots. The elongated horizontal stem is located underground, where temperature changes and drought have less effect on the vital activity of the plant. And the supply of water and nutrients greatly increases the chances of the plant organism to survive.
Many have come across a situation where you need to get rid of the annoying couch grass, overgrown lilies of the valley or other plants with rhizomes. It is not so easy to do this. Modified shoots grow strongly, their parts often remain in the ground, forming new shoots. But, on the other hand, this ability is often used for vegetative propagation of plants.
Tuber
Tuber is a modified shoot that is also underground and stores nutrients. Everyone knows potato tubers, which are of great economic importance. They accumulate large amounts of starch.
Some mistakenly believe this modified shoot is a fruit. In fact, potato fruits are formed on above-ground shoots after flowering. The tuber is a thickened stem with apical and lateral buds - eyes. Germinating, the eyes form young shoots.
Elongated oblong and short-lived shoots are also called stolons.
Plants such as saffron and gladiolus have a corm - a thickened stem with adventitious roots. Protects the inner contents of the corm with a layer of dead leaves.
Onion
Onion, garlic, tulip and lily have another modification - an onion. On a flat stem, which is called the bottom, are the kidneys. Several types of scaly leaves develop from them. Some of them are thick and fleshy. They store water with nutrients, providing life to the plant. They are protected from above.dry membranous leaves. Young onion leaves, the so-called green onions, grow from dormant buds on the bottom. Bulbs are also typical for plants of the steppe natural zone. In conditions of cold winters with little snow and hot dry summers, this modification enables the plant underground to survive the unfavorable period in this form.
Above-ground modifications of shoots
Modified shoots of plants can also be above the ground. So, on the branches of hawthorn and blackthorn there are thorns - shortened and lignified modified shoots. They are the result of branching and sharpening of the stem, reliably protecting their owners from being eaten by animals. Plants with thorns have tasty, juicy fruits with bright colors, so they need extra protection.
Strawberries and wild strawberries have an additional device for vegetative propagation - elongated mustache shoots. They are fixed in the soil, forming a new plant.
Mustache should not be confused with grape tendrils. They have a completely different functionality. With the help of tendrils, the plant is attached to the support, occupying the most advantageous position in relation to the sun. Such a device is also characteristic of pumpkin, cucumber, watermelon.
Modifications of shoots in the direction of growth
Depending on the growing conditions, the shoots can also change. In woody and herbaceous plants, erect stems are most often found, directed towardssun. Creeping and creeping stems grow very quickly, cover the surface of the soil with shoots with leaves. This provides them with a prosperous existence. Plants with climbing stems are called vines. They are typical for tropical and humid equatorial forests, although they are often found in the temperate zone. To attach to the support, creepers use special devices: hooks, trailers, bristles.
Internal structure of shoot modifications
Despite external differences, various modifications retain all the features of the internal structure. For example, a potato tuber, being a thickened stem, is covered with bark on top. This is what we peel off when we peel potatoes. On the longitudinal section of the tuber, a dark strip is clearly visible - wood. And in the core, loose basic 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 leukoplasts, in which starch accumulates, turn into green plastids chloroplasts in the light. Such a product should not be eaten because it contains the alkaloid solanine, which is poisonous to the body and causes poisoning.
Functions of modified shoots
It is the modified shoots that determine the survival of plants in adverse conditions. By storing valuable nutrients, they allow plants to survive during periods of drought. Biennial and perennial plants survive only thanks 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, feeding on stocks of thickened stems. With the onset of heat, the plant resumes growth again.
Many modifications of the shoot are used for vegetative propagation, quickly increasing the number of valuable plants. This property is actively used by man in agriculture.
Origin of flower
A flower is a modified shoot. It is very easy to prove this fact. It develops from a specialized generative kidney. This part of the shoot acquires characteristic features to perform the most important additional function - the sexual reproduction of plants. That's what a flower is for. The modified shoot is significantly shortened compared to ordinary stems. Its main parts are the stamen and pistil, which contain the sex cells - sperm and egg, respectively. The bright color of the flower petals is needed to attract pollinating insects. Small flowers are collected in groups - inflorescences. This way they are much more noticeable, and their aroma spreads more strongly.
After pollination and fertilization, a fruit is formed in place of the flower. It consists of seeds and pericarp. Seeds give rise to a new plant, and the pericarp nourishes and warms them.
In addition, a flower is a modified shoot that has been giving people aesthetic pleasure for many centuries, inspiring poets and musicians.
Modified shootsare 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 due to the need for the emergence of new functions in constantly changing living conditions.
