The "waist pole" of plants
As the saying goes, a healthy person has a tough waist. In other words, a healthy person's waist is straight and not hunched. In fact, plants are the same as people; Normal growing trees with straight and towering stems; Most of the crooked branches are not healthy trees. Therefore. It is no exaggeration to call the stem the "waist pole" of a plant.
The tallest tree in the world is Sequoia, with a height of over 100 m and a trunk diameter of over 10 m. Its grandeur is due to the decisive role played by the stem. Cephalotaxus fortunei in Xishuangbanna, China is a broad-leaved tree with a trunk as high as 40 meters.
Because looking up at its treetops is like looking up at the sky, people call it a tree looking up at the sky.
Sunflower is millet, which can reach more than 3 meters high, with thick stems and a large flowerpot (flower head) like a washbasin at the top-if there is no solid stem, it can't support such a large flowerpot anyway.
Even those small herbs have straight stems. Although the small stems look extremely slender, they stand upright without bending. For example, shepherd's purse, which grows on the grass in spring, will be full of flowers at the top of its stem, and at the same time of flowering, the stem will grow up and grow new flowers constantly.
Ranunculus is a plant that grows in water. Although its stems and leaves are not hard and both grow underwater, when it is about to bloom, it will produce straight stems and lift the flowers out of the water for insects to pollinate.
Whether tall and strong or short and slender, the stems of plants have the same function, that is, supporting the body and expanding the space as much as possible. There are branches on the trunk of plants, small branches grow on the branches, and leaves grow on the small branches, which can spread the leaves, get the nourishment of sunlight, carry out photosynthesis, and make nutrients for their own survival.
The reason why plants can stand the test of wind and rain lies largely in the structure of stems: there are powerful supporting mechanical tissues (composed of thick-walled cells) in the stems of plants.
The "transportation line" of plants
In addition to supporting the body, the stems of plants also have a very important function-transporting water and nutrients.
The water needed for plant growth and the inorganic salts in the water are all in the soil. Through roots, plants can absorb these water and inorganic salts, but to transport them to branches and leaves, they must pass through stems.
The roots of plants have root pressure, which can make water go up; Leaves have the ability to absorb water through photosynthesis, which makes the water in roots rise continuously. The lifting path is in the stem. There are vascular bundles in the stems of plants, and one of them (composed of vascular molecules) is like a tap water pipe, which can let water flow through and transport it upward to the branches and leaves for photosynthesis. Another kind of pipeline in vascular bundle is composed of sieve tube molecules, which is specially used to transport nutrients made by leaves and transport them down to the roots to meet the growth needs of various parts of plants.
All kinds of stems
Due to the complex external environment of plant growth, the shapes of plant stems are also strange, not all of them are straight and towering.
As we all know, the leaves of plants are germinated by buds on stems and branches. The sprouting place is the node on the stem. After the tree leaves, you can see a bud falling off at the petiole. When the buds germinate in the second year, branchlets can be produced, with leaves on the branchlets and buds in the axils. If this renewal continues, new leaves will be issued every year, new buds will be born, and life will continue. If there are no buds on the "branches" we see, it may not be stems, but roots, because leaves will not grow on the roots of plants.
In this way, we know that "there are nodes on the stem, leaves on the nodes, and buds in the axils of leaves".
Leafy stem
Acorn stems are similar to leaves, and its eggs are round and flat. Its shape is almost the same as the leaves of ordinary plants, but in fact, it is the stem of an acorn.
This "leaf" of oak is formed by flattening the stem and branches, which botanists call leaflike branches (branches are deformed into leaf shapes). The leaflike branches are oval and hard. This kind of stem of acorn tree is the result of adapting to dry environment. Flat branches contain chlorophyll, which can replace leaves for photosynthesis to make nutrients. Real leaves degenerate into tiny scales, which can hardly be seen without careful look. This degraded leaf has lost chlorophyll because it is not needed for photosynthesis.
The degradation of leaves can reduce the transpiration of water, which is beneficial to resist the drought environment, while the flattening of stems and branches can not only not carry out photosynthesis, but also lose the ability to make nutrients.
Acorn belongs to the genus Acorn in Liliaceae. It is a semi-shrubby plant, which grows in the arid area of the Mediterranean. The flowers of oak trees are unisexual and dioecious.
Perhaps some readers will ask: Why do botanists think that the leaves of fake trees are stems, not leaves? In fact, as long as you observe the growth position of flowers and fruits of oak trees, you will understand everything. Oak flowers and fruits are born in the center of leafy branches, that is, midvein, which proves that the central part is the branch itself (because flowers and fruits of plants are born on branches, not leaves), and objects with flat sides are the flat parts of branches.
Acorn trees are not only interesting in Ye Jia, but also have beautiful red fruits, which are rich in ornamental value. China has introduced it as a bonsai. Its reproduction can be carried out by branching.
The potato itself is the stem.
The potato that we often eat is itself a kind of stem. Botany calls this abnormal stem "tuber".
Some people may ask, how can potatoes be stalks? If you look closely, you will find some small depressions on the surface of potatoes. These depressions are called "bud eyes" and there are buds in them. If potatoes are planted in the soil, the buds in the potato depression will sprout and grow branches and leaves.
Under normal circumstances, plants have nodes on their stems and leaves on the nodes. Buds are born in the axils of leaves (the junction of leaves and stems), and buds can produce branches and leaves.
So, where is the potato festival? There is a trace on the edge of the potato depression, and there is a thin irregular thing on the trace. In fact, the depression of the potato is the node from which the bud grows. Then grow branches and leaves. Potato nodes originally had leaves, but the leaves have degenerated into residual thin slices, and there are no green cords. In this way, potatoes completely conform to the characteristics of stems.
Potato is a kind of deformed stem, and its expansion plays a role in storing nutrients.
Potatoes contain a variety of nutrients, rich in vitamins, especially vitamin C, which can resist scurvy. Sailors in ancient times often took potatoes with them to eat on the trip to prevent discord. In addition, potatoes also contain protein, phosphorus, iron and inorganic salts.
Potato belongs to Solanum of Solanaceae, which originated in the Andes of South America. It was introduced to Europe in the16th century and became the main food source for Europeans. Potato was first cultivated in China in the late Ming Dynasty, first in North China, and then gradually spread to all parts of the country.
rhizomatous root
The stems of plants are generally slender cylindrical and grow on the ground; If it grows in the soil. It is often mistaken for the root of a plant. But some plants have long stems in the soil, thin and long, just like roots. In botany, this underground stem is called rhizome or rhizome.
Many herbs have rhizomes, such as Polygonatum odoratum, whose rhizomes are white and have nodes and internodes like bamboo (the part between two nodes is called internodes), which completely conforms to the characteristics of stems. The underground part of another plant-seven leaves and one flower is mainly rhizome.
There are many fine hairs on the roots of the two plants mentioned above, which are their real roots.
In addition, the underground part of bamboo is called bamboo whip, which is also the rhizome. There are buds on the bamboo whip, which can grow bamboo.
Spherical stem.
The end of the underground stem of some plants becomes hypertrophy, which looks like a regular ball, oval or oblate. This sphere is deformed from the top of the underground stem and is often called a "ball".
Careful people will find that bulbs have many characteristics of stems: there are obvious nodes and internodes on bulbs, and there are membranous scales and a few buds on nodes.
The function of the ball is to store nutrients, which is convenient for plants to overwinter.
Typical bulbous plants are arrowhead and water chestnut. The former belongs to arrowhead of Alismataceae, and the latter belongs to Eleocharis tuberosa of Cyperaceae. Both are aquatic plants, and bulbs are edible.
Lily is a very interesting plant, and its underground part is a white or light brown sphere. This bulb is not the root of lily, but its stem, which is called "bulb" in botany.
Lily has many thick white scales on its bulb. If you peel off these scales one by one, you will find a conical thing in the center of the bulb, and all the scales grow on it. In fact, that cone-shaped thing is the stem of lily, and those scales are the leaves of lily. Deformed leaves grow on deformed stems, forming a unique lily bulb.
Lily belongs to Liliaceae, belonging to 80 species, all of which have bulbs, but different kinds of bulbs are large and small, and their colors are different. Bulbs not only have scales, but also buds. Lily can reproduce with bulbs.
Besides Lilium, Allium, such as onion, garlic and onion, all have bulbs. Some flowers, such as daffodils and tulips, also have bulbs.
Bulbs play an important role in plants. Lily plants usually grow in shallow soil on cliffs. Because they can store nutrients and water through bulbs, plants can grow in places where water and nutrient conditions are not ideal. What is even more amazing is that even if the flower branches on the ground are damaged, as long as the underground bulbs are intact, new branches and leaves can still grow and flowers will bloom. It can be seen that bulb is the reproductive organ of Shandan flower.
Compared with lily bulbs, arrowhead bulbs and water chestnut bulbs are not as thick as scales, and their leaves are thinner. But both bulbs and corms can be used for reproduction, and in this respect, they are similar.
Spiny stem
There are many hard thorns on the trunk of Gleditsia sinensis, and there are branches on the thorns. In fact, these thorns on the Gleditsia sinensis tree are branches, and their properties are the same as those of the stems. They are a kind of deformation of the stem.
Gleditsia sinensis has sharp thorns, which has certain protective effect on trees.
Gleditsia sinensis belongs to Leguminosae, a deciduous tree with pinnate compound leaves, yellow-white flowers and fleshy fruit, which can reach 30 cm long. Gleditsia sinensis is almost all over the country, and its juice can be used as soap; Hard thorn can be used as medicine, which has the function of promoting blood circulation and reducing swelling, and is called "Gleditsia sinensis". In autumn, people often cut off the hard thorns on the soap feet, cut them into pieces and dry them in the sun for later use.
It should be noted that the thorns on plants are not all branches, that is, deformed stems. For example, there are thorns on the branches of roses, Chinese rose and Chinese rose, but these thorns are skin thorns, which are formed by epidermal cells of stems and branches, not branches, which are very different from Gleditsia sinensis. The thorns are small and easy to remove by hand, while the hard thorns on the Gleditsia sinensis tree are not easy to remove.
The thorns of elm (Ulmaceae), citrus fruit trees (Rutaceae) and rhamnaceae are all hard branches. The thorns of Robinia pseudoacacia (Leguminosae), Zizyphus jujuba and Zizyphus jujuba are abnormal leaf thorns which are metamorphosed from stipules.
Stem and our life
The stems of plants are of great use to human beings.
Trees are building materials. In the buildings of the Ming Tombs in Beijing, there are columns made of a single trunk, which is nanmu of Lauraceae. This kind of wood is hard, antiseptic and insect-proof, and can be preserved for thousands of years.
In the past, sleepers on railways were also made of tree trunks.
Bamboo is also a common building material, such as Daijia Bamboo House in Xishuangbanna. Beautiful and chic.
The stems of some trees can also provide food for human beings, such as the sago coconut tree of Palmae, whose trunk is rich in starch. Peel off the trunk and take out the starch, and you can make "West Gu Mi". "West Gu Mi" is white and crystal clear, such as high-quality rice, which has a unique flavor and can be eaten. Therefore, the locals call Xigu coconut tree "rice tree".
A large part of the sugar we often eat comes from the stems of sugarcane. The stems of Canadian sugar maple are rich in sugar, which can be made into maple sugar after refining.
The stems of some plants are rich in tough fibers, which can be used for weaving or making ropes. For example, ramie fiber can be used to make summer cloth, and hemp and jute fiber can be used to make sacks and ropes.
The stems of some plants are still medicinal materials. Motherwort can grow to more than one meter high, and the whole grass can be used as medicine. Among them, the stems of Leonurus japonicus account for a large proportion. Gastrodia elata is an important drug for relieving spasm and expelling wind, which can treat dizziness and headache. Polygonatum sibiricum of Liliaceae, born in soil, can be eaten or processed into medicinal materials, which has nourishing effect similar to ginseng. Cinchona bark contains quinine, and Eucommia bark can treat hypertension.
Some plants in the desert are as rich in water as cactus stems, which travelers can use to replenish water. The trunk of Hu Yangmu is also rich in water, so you can dig wells to get water.
In addition, there is a vine in the tropical forest, which stores water like a tap water pipe and can be cut and drunk directly.
The stems and skins of other plants are very useful. European cork oak has a thick cork layer, which can be cut off to make cork and soles.
In Sicily, Italy, there is a very tall chestnut tree with a hollow trunk, which is used as a storage room by local people.
Expensive furniture is mostly made from the trunk of leguminous plants, such as rosewood, Dalbergia odorifera, rosewood and so on.
In addition, lacquer tree trunks contain raw lacquer, pine tree trunks contain turpentine, rubber tree trunks contain rubber, reed stems can make paper, and so on.