the embryo root appears first from the seed peel. At first it is slightly noticeable, but soon it stretches out and becomes large. Why is this happening?
The root of the embryo and the root of the adult plant, like all other organs, have cell structure. Germ root cells absorb seed nutrient solutions, grow and divide.
If one draws transverse dashes on the sprout of pea seedlings with mascara at a distance of 2 mm from each other and places the seedlings in a bottle with water poured on the bottom, in a day the distance between the marks located near the root tip will increase. This will happen because there is a site where young cells divide and grow. As a result of the division of these cells, new ones are formed - daughter cells. The daughter cells, in turn, divide and grow. So the small root gradually turns into a large root.
The root grows in the apex. It is not difficult to verify the validity of such a conclusion.
If you tear off or trim the tip root - its top, the growth of the root in length will stop. At the root with a torn tip, many lateral and adnexal roots are formed. The root system is becoming more powerful. Each of the lateral roots also grows with the apex. This root property is used when transplanting seedlings of cabbage, tomatoes, asters and other cultivated plants that have a root root system. Pinch the root during a dive.
Pick - this is pinching the root tip when planting young plants with a pointed peg resembling a peak.
From the name of the peg - peaks, pickets - this process got its name. Pickling seedlings causes the growth of lateral and subordinate roots and their growth in the upper, most fertile soil layer 25 . So, in corn, the root system grows away from the stalk almost 2 m, and onions - 60-70 cm.
Tree roots grow especially hard. For example, in an adult apple tree, they grow laterally up to 15 m from the trunk of the plant, and in depth up to 3-4 m. Most of the roots develop at a depth of 15-18 cm from the soil surface. Therefore, you can’t grow vegetables, field crops or any other crops under the crowns of fruit trees.
The total length of all the roots of one plant is very large. For example, carrot roots are about 7 times longer than the aerial parts of the plant. Due to the proliferation of root systems, plants receive more nutrients from the soil. The root systems of different plants grow differently in the soil. In some, they go far deeper, in others they spread in breadth at a shallow depth 26 .
1. In what section of the root does it grow? How can this be proved?
2. What happens to the root if it cuts off the top?
3. What is a pick? What is its purpose?
4. How do the roots of different plants grow in the soil?
5. Why can not grow vegetables under the crowns of fruit trees?
\u003e Grow a few bean or pea seedlings, place them in bottles with a small amount of water, attaching the seedlings to the corks with which the bottles are closed. Before this, half of the seedlings pinch off the third part of the root. Observe how the intact and pinched roots of the seedlings will grow. After a week, dry the seedlings, attach them to a piece of thick paper and draw conclusions.
Korchagina V. A., Biology: Plants, bacteria, fungi, lichens: Textbook. for 6 cl. wednesday school - 24th ed. - M .: Education, 2003 .-- 256 p.: Ill.
Lesson content lesson summary support frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-examination workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Artwork audio, video clips and multimedia photos, pictures, charts, tables, diagrams humor, jokes, jokes, comics parables, sayings, crosswords, quotes Additions abstracts articles chips for curious cheat sheets textbooks basic and additional glossary of terms other Improving textbooks and lessons correction of errors in the textbook updating a fragment in a textbook elements of innovation in the lesson replacing obsolete knowledge with new For teachers only perfect lessons annual schedule methodological recommendations of the discussion program Integrated lessonsThe roots differ in shape ( types of root systems):
- Rod, which are a direct continuation of the stem into the ground and characteristic of most dicotyledonous plants. By origin, this will be the main root. The root root may be: threadlike, fusiform, onions, branches (Fig. 57, 1 —4 ).
- Hairy the roots. In large numbers, they depart from the base of the stem, have more or less the same thickness. Fibrous roots are found in monocotyledonous plants (for example, cereals). By origin, these will be subordinate roots (Fig. 57, 5 ).
When developing from a seed, the root usually grows at first much, much faster than the aerial part of the plant. The depth of penetration of the roots into the soil is very significant. The total length of the roots far exceeds the length of the aerial parts of the plant. At butyak eg ( Cirsiumarvense), malicious weed of our fields, the root penetrates to a depth of over 6 m. at the camel spine (Alhagicamelorum) growing in the deserts of Central Asia, the roots go deeper into the ground to 20 meters or more, ensuring the delivery of water to the plant from deep subsoil layers. This gives her the opportunity to keep the leaves fresh in the hottest period, when other plants burn out. In ordinary onion roots penetrate to a depth of 1 m The diameter of its root system is approximately 60 cm.
The total length of the roots is also expressed by a solid figure. In the majority of cultivated cereals, it equals 500-600 m and in spring rye the total length of the roots of the 1st, 2nd and 3rd orders turned out to be 80 km The total surface of the root system of winter rye reaches 237 m 2 and exceeds the surface of the aerial parts by almost 130 times.
The root grows its the top. When cutting off the root, a powerful development of lateral roots is observed. This root feature is used when picky plants (in horticulture and truck farming). When picking, the plant is transplanted and the main root is shortened by 1/2 - 1/3 of its length, which causes abundant branching of the remaining part, providing powerful growth of the root system.
The endings of the main, lateral and subordinate roots and their smallest branches are dressed outside with the so-called root covers - a complex of cells, constantly erasing and desquamating. In their place there are new cells. Due to the mucilage of the shells of the outer cells of the cap, the root growth among the solid particles of the soil is facilitated. Cells of the cap protect the root growth cone from damage (Fig. 58). The root cap is present in all land plants. In aquatic plants, when their roots grow in water, a cap is not formed. When they are rooted in the soil, a cap develops at the ends of the roots. Material from the site
Slightly above the tip of the root in a narrow space of several centimeters are located on the entire outer surface of the root the so-called root hairs, which are outgrowths of cells of the epidermis of the root. Through them, water and nutrient salts enter the plant. Root hairs with thick felt cover this so-called root absorptive zone. The total length of root hairs in one plant reaches a huge value. According to the calculations, the length of all root hairs of one specimen of wheat reaches 20 km As a result, the absorbing surface of the root increases 10–15–20 times.
The main root grows steeply down, perpendicular to the surface of the earth. This phenomenon is called positive geotropism. The lateral roots grow almost horizontally (they transversely geotropic) Smaller root branches do not have geotropicity. Roots never form or carry leaves and their primordia.
The root grows in length using the apical point of growth. A growth point (meristem) is a group of cells capable of active cell division. It is located not at the very end of the root, but under the root cover, which protects it from
damage and facilitates the advancement of the root in the soil during growth. The latter function is carried out due to the property of the outer walls of the root cap covered with mucus, which reduces friction between the root and particles of soil. In some plants, the cells of the root cap are very strong and able to push apart soil particles. The root cap is present on the roots of all land plants and is absent in many hydrophytes.
Root cap cells are live, often containing starch grains. Cells of the outer layer of the cap are desquamated. As they die, the cap is restored from the inside due to cells formed by the growth point (in dicotyledons) or by its separate meristem (in monocotyledons).
The cells of the root growth point (apical meristem) actively divide, the length of this zone in different species and in different roots of the same plant is not the same. So, the meristematic zone of the growth roots of pedunculate oak is 250-2000 microns, and for sucking roots - 45-65 microns; in maple acutifolia, respectively - 200-300 and 50-150 microns.
Behind the division zone there is a stretch zone (it is called a growth zone). The length of this zone does not exceed several millimeters (for tobacco - 320 microns; for corn - 7; for beans - 5 mm).
As linear growth is completed, the third stage of root formation begins - its differentiation, a zone of differentiation and specialization of cells (or zone of root hairs and absorption) is formed. In this zone, the outer layer of the epiblema (rhizoderm) with root hairs, the layer of the primary cortex and the central cylinder are already distinguished (Fig. 1).
The epilemma consists of one layer of thin-walled and tightly closed cells, capable of forming root hairs. The length of root hairs is 0.15–8 mm (for orchids — up to 3, for cereals — 1.2–1.5, for misfits — 2.4 mm); especially large hairs on the roots of the cuttings, are larger in herbaceous plants than in woody ones. The shell of the hair is very thin (0.6-1 microns), which facilitates the absorption of nutrients). Almost the entire hair cell is occupied by a vacuole surrounded by a thin layer of cytoplasm. The nucleus is at the top of the cell. A mucous membrane forms around the cell (due to pectin shell materials), which promotes the bonding of root hairs with soil particles, which improves their contact and increases the hydrophilicity of the system. Absorption is also promoted by the allocation by the root hairs of acids (carbonic, malic, citric, oxalic), which dissolve the mineral salts.
Root hairs also play a mechanical role - they serve as a support for the apex of the root, which passes between the particles of soil. Root hairs form very quickly (in young apple seedlings in 30-40 hours). Their number per 1 mm 2 of the root surface under the conditions of a wet chamber in corn is 425, in an apple tree - about 300, in peas - 230, which, in terms of the entire plant, amounts to billions. Root hairs do not function long. As the root grows, dead hairs are replaced with new ones.
The primary cortex consists of many layers of living cells. The membranes of the cells of the outer layers (exoderm) are able to thicken. After the death of the epiblema, these layers of the cortex perform a protective function. The inner layer of the cortex (endoderm) also has thickened shells. The endoderm consists of one row of cells forming a dense ring without intercellular spaces around the central part of the root. Sometimes there is a two-row endoderm (Schisandra chinensis). The thickenings on the thin radial walls of its cells (Caspari belts) form a continuous system of thickenings around the central cylinder.
The central cylinder consists of a conductive system, surrounded on the outside by a ring of living cells that are capable of dividing and are called the pericycle. Due to the division of pericycle cells, lateral roots are formed. In the pericycle, additional buds can also be laid, which then develop into aerial shoots - root sprouts (such sprouts form poplar, aspen, willow, lilac, raspberry, blackberry and other plants).
The root conduction system conducts water and minerals from the root to the stem (upward current) and organic matter from the stem to the root (downward current). It consists of vascular-fibrous bundles. The main components of the beam are phloem sections (along which substances move to the root) and xylem (along which substances move from the root). The main conductive elements of the phloem are sieve tubes, xylem - trachea (vessels) and tracheids. Parenchymal cells and cells of the mechanical tissue of the sclerenchyma are associated with the conductive elements of the phloem and xylem.