What are the characteristics of the roots and stems of plants?

Dicotyledon.

The primary structure of rhizomes is composed of three parts: epidermis, cortex and vascular column. 1. The epidermis is developed from the original epidermis. Roots (generally composed of a single layer of cells, without stomata. Epidermal cell wall.

protruding outwards and extending to form root hairs); Stems (composed of living cells, with stomata. The outer wall of epidermal cells is thicker and usually keratinized and forms a stratum corneum.

2: The cortex, located in the inner epidermis, is developed from basic meristems.

Roots (composed of multi-layered corbored cells, the cells are loosely arranged, often with significant intercellular space, and occupy a considerable part of the root. It can usually be divided into the outer cortex, cortical parenchyma and endothelium); Stem (composed of multiple layers of living cells. It is not as well developed as the cortex of the root, accounting for only a small part of the stem, and the cortex cell wall is thin and large, loosely arranged, with intercellular space, and the cells near the epidermis often contain chloroplasts.

Therefore, the young stems are mostly green and can carry out photosynthesis.

The basic component is parenchyma, which often has thick horns in the area immediately adjacent to the epidermis. Some plants also have fibers, stone cells, or secretory tissues in the cortex). Three:

The vascular column, all the tissue structures within the endothelial layer of the root are collectively called vascular columns, and the structural table is more complex, including three parts: the middle column sheath, the primary xylem and the primary phloem, and some plants also have the medulla. The development and maturation of the primary phloem is also the external initiation style, that is, the primary phloem is on the outside and the posterior phloem is on the inside. Between the primary xylem and the primary phloem is parenchyma.

The vascular columns of the stem are located within the cortex and occupy a larger part of the stem, including the vascular bundles arranged in a ring.

medullary rays and medulla, etc. Vascular columns used to be referred to as the middle column.

There are a large number of wood fibers and bast fibers in the stem, so it is relatively strong, and these cells are slender in shape, and the composition of the wall is particularly thick, which is similar to the support of human bones, and is a mechanical tissue.

The stem tip is similar to the root tip and has the ability to grow indefinitely; The tips of the stems continue to grow, producing leaves and lateral branches, which, with the exception of a few underground stems, together form a large branch system of the aboveground part of the plant body.

The morphological stem is a general term for the main stem and the branches with it as the main axis. The shape of the stem of the seed plant is cylindrical, and the stems of many plants show other shapes, such as the triangular stem of the sedge, the square cylindrical stem of plants such as mint and broad bean, and the flat stem of the cactus.

As the plant grows, a variety of lateral organs develop on the stem, including leaves, branches, buds, flowers, or fruits. In addition to the main components mentioned above, the branches have many special morphological characteristics.

1. Epidermis: The stem epidermis is usually keratinized, with cuticles and stomata. The root epidermis is not keratinized, there are no stomata, and some of the root apical epidermis produce root hairs.

2. Cortex: The stem cortex is very thin, except for parenchyma, it includes various tissues, and most of the endothelial layer is inconspicuous or absent. The root cortex is thick, mostly thin-walled, and sometimes has various tissues.

3. Vascular column: the stem usually does not contain a middle sheath, the boundary between the vascular column and the cortex is not obvious, and the differentiation of the vascular system is related to the occurrence of leaves, protoxylem and protophloem. The inner and outer are arranged to form vascular bundles, the order of differentiation, with the main xylem starting internally and the main phloem being external, usually the bone marrow.

Stem characteristics of plants: according to the texture of the stem, there are woody stems and grassy stems.

Xylotic stem In the internal structure of the stem, there are many lignified cells, and the texture of the stem is firm and usually tall, which is called a woody stem. Plants with woody stems are called woody plants. Woody plants are all perennials.

It can generally grow for decades to hundreds of years. It does not die throughout its life, either above ground or underground.

Grassy stem In the internal structure of the stem, there are no or very few lignified cells, and the stem is weak and often remains green, which is called the grassy stem. Any plant that has a grassy stem is called a herbaceous plant. The stems of herbaceous plants do not grow very thick, and the lifespan is short, generally annual and biennial, and a few are perennial.

According to the growth mode of the stem, there are seven types: erect stem, winding stem, climbing stem, reclining stem, oblique ascending stem, lying stem and stolon.

According to the change of stems, there are stem tendrils, stem thorns, rhizomes, tubers, bulbs, bulbs, etc.

The morphology of the stem is varied, there are thick and thin, long and short, and it varies greatly, with a height of more than 150 meters and a diameter of more than 10 meters; The low ones are only a few centimeters; Plants that can grow up to 200 300 meters long and have no stems are extremely rare. The phrase "no above-ground stems" is usually referred to as "no above-ground stems", which is essentially very short or inconspicuous above-ground stems, and by no means no above-ground stems. Most of the stems are round, but some plants have square stems, such as broad beans, desmodium and other herbaceous plants; The stems of a few plants are flattened, such as cacti and knotweeds.

On the stem of any plant, knots can be seen, which is crucial and is the most essential feature of the stem. knots, which are evident on the stems of certain plants, such as moso bamboo, corn, sugar cane. On the stems of these plants, at intervals, you can see a ring of protrusions, which are called knots.

These nodes are always noticeable on young stems and old stems. However, there are a considerable number of plants whose nodes on the stems are not as clear as those of the above-mentioned plants, especially on the old stems, and it is not clear where the nodes are. Between knots is called internodes.

The length of the internodes varies even at different growth stages of the same plant. The extremely short internodes make the whole stem shrink into a flat disc, and there seems to be no stem on the outside, such as the internode of the onion stem is extremely short, the nodes are very close, and the stem appears very short.

The stem is the aboveground part of the organ formed by the long-term adaptation of higher plants to land life, and it generally has the habit of growing to the ground. The lower part of the stem connects the roots, and there are nodes and internodes on the stem, and leaves and flowers and fruits are born on the nodes. There are buds at the top of the stem, called the apical bud, and the buds on the side are called lateral buds.

The main function of the stem is to play a role in transport and support, through which the stem can transport the substances absorbed by the root to all parts of the plant body, and at the same time, it can also transport the products of the plant in the process of photosynthesis to various places required by the plant body.

The stem also plays a supporting role, supporting the leaves, flowers, and fruits of the plant body to stretch out to the space on all sides, and supporting the plant body to resist adverse natural conditions such as wind, rain, and snow. In addition, stems also have a storage and propagation function.

1. The plant infrastructure is different.

The roots do not grow leaves, there are no nodes and internodes, and there are generally no buds. Stems have rhizomes, tubers, bulbs, etc.

2. The growth environment is different.

The stems grow on the upper end of the plant, while the roots grow on the lower end of the plant and depend on the nutrients of the soil to survive.

3. The surface texture and shape of the rhizome are different.

The surface of the root is often textured, and some of the skin pores are visible, and the structure of the "Kjeldahl zone" of plant cells on the surface affects the texture structure of the epidermis.

The upper part of the stem generally has a thicker root node, and the root node is commonly known as "reed head", and the texture of the reed head is relatively rough. The stem must have knots, and no matter what kind of stem it is, knots can be found, while there are no knots in the roots. Of course, some of the roots also appear to have nodes, but it can be observed that these "nodes" are formed by the scaly surface of production.

The stem has long leaves, and no matter what type of rhizome, it will grow leaves, and there are buds in the leaf axils, and some of these buds will grow branches, so the branches will always grow on the buds.

Definition of stem.

The backbone of the aboveground part of a vascular plant with leaves, flowers, and fruits. It has the function of transporting nutrients and water and supporting leaves, flowers and fruits in a certain space. Some stems also have the functions of photosynthesis, nutrient storage and reproduction.

The position of the leaves on the stem is called the node, and the part between the two nodes is called the internode. There are buds at the tip of the stem and in the axils of the leaves on the nodes, and when the leaves fall off, there are traces left on the nodes called leaf marks. The morphological characteristics of these stems can be distinguished from those of roots.

Most seed plant stems are cylindrical in shape, but a few plants have other shapes, such as the sedge family, the Lamiaceae stem, and some cacti with oblate or polygonal columnar stems. On the shape of the stem of the woody plant, you can also see the marks of bud scales, which can be seen when the sapling or branch develops every year, so that the age of the sapling or branch can be calculated.

root root

Concept The root is the underground part of the axis of the vascular plant body (in this picture, the aerial root), which mainly plays the role of fixation and absorption, as well as the synthesis and storage of organic matter, as well as the function of vegetative reproduction. Leaves and flowers do not grow on the root, and although it has branches like the stem, the branches (lateral roots)** are different. Algae and bryophytes have no roots, and the most primitive of ferns, the pine-leaved fern, the Macy's fern, and the earliest terrestrial fossil of antiquity, the Lenny fern, have no real roots, and only have false roots with absorption function on the rhizomes underground; Most extant ferns, gymnosperms, and angiosperms have a true root structure.

Roots are the organs of terrestrial plants that absorb water and inorganic salts from the soil, and are also the organs that fix the body of above-ground plants.

Most plant stems are cylindrical in shape, but a few plant stems have other shapes. The root is the underground part of the plant body, and the root does not grow leaves and flowers, although it has branches like the stem, but the branches are different.

Because the high speed of the root will not spill the group, the external users have good and bad mouths, and the quasi-hqaq Hu Olympic Committee should pay attention to the dead sights.