Why are there so many colorful and varied plants in nature? Because every plant can only grow and develop under its environmental conditions, but the environmental conditions are ever-changing and constantly changing, and plants must constantly mutate and update to adapt. Some new traits can be passed on to offspring, and new offspring may produce new variations. Plants have both the heredity of self-replication and the particularity of constant variation. Because of variation, the plant kingdom can gradually develop from the simplest primitive single-celled plants to parallel synthetic groups, and then evolve from groups to multicellular plants. This series of evolutionary processes from simple to complex, from low to high, are closely related to the changes of external environmental conditions. Here are some plants that live in different environments. Aquatic plants The existing aquatic flowering plants are a secondary phenomenon that terrestrial plants return to the water again. Part of the whole plant sinks into the water; Some plants have leaves floating on the water, or only some plants are exposed to the water. For example, Ceratophyllum and Myriophyllum are submerged plants; Its epidermal cell wall becomes very thin, without cuticle, waxy layer and cork layer; All parts of plants can directly absorb water and inorganic salts from water, so the roots are often degraded or only used for fixation; The transportation system is also weakened, but the air in the water is very thin, so there are many large air chambers in the body, which can store a lot of air, on the one hand, it is helpful for gas exchange during photosynthesis and respiration; At the same time, this plant can float on the upper water without sinking. Its leaves are subdivided into filaments, which is the characteristic of adapting to the weak light in water. Subdivided leaves can increase the contact surface with light, and chloroplasts in stems, leaves and epidermal cells can enhance the ability to utilize light energy. Other plants, such as Eichhornia crassipes, have a balloon like fenugreek in the middle of the petiole. The water turtle air chamber is located on the back of each blade. Polypodiaceae produces many rod-shaped white respiratory roots on plants, which are filled with air. These are special floating devices that allow plants to float on the water and get enough sunshine and air. These plants are called floating plants. There are also aquatic plants such as cattail and water chestnut; Most plants stand out of the water, and the demand for sunshine and air can be met; But the lower part is submerged in water, and the gas exchange is still difficult, so the ventilation tissue in the body is also very developed. The climate of arid desert plants is very dry, with little annual rainfall (only tens of millimeters or even several millimeters), 60% ~ 80% of which is concentrated in summer, and it is drier at other times. Due to the serious water shortage in soil, salinization often occurs. Organic matter is extremely scarce. In order to survive in such an environment, plants must have the ability to resist extreme drought; Enhance water absorption, reduce water loss and store a lot of water. But different species have different ways to resist drought; For example, some species of cactus (figure 1) and Euphorbia humilis can live in desert areas because their stems become fat and fleshy, their leaves degenerate, and the parenchyma cells in their bodies can store a lot of water; The stored water can sometimes reach 95% of its own weight. At the same time, the surface of the body is keratinized and the stomata are deeply sunken. There is rich mucus in cells, which can make water evaporate very slowly. Can still maintain life under the condition of long-term water shortage. Someone has done such an experiment: 1 cactus weighing 37.8 Jin was moved indoors, and there was no water supply for 6 years. After six years, this cactus only evaporated 1 1 kg of water. In short, the overall metabolism of xerophytes is extremely slow. This is their adaptability in struggle for existence. Halophytes exist in saline soil, no matter on the coast, inland arid lakes or near salt lakes. Besides salt, there are gypsum, calcium salt and magnesium salt in the soil. Exchangeable sodium in saline soil can be added with water to generate sodium hydroxide, and then combined with carbon dioxide in soil to generate sodium carbonate, which becomes alkaline earth. Plants in this high-salt living environment can't grow, but some plants like high salt and have special adaptability, so they can survive here for generations. For example: Tribulus terrestris, Saida, Glaucus, etc. They have strong adaptability to different temperatures and altitudes. As long as it is salty soil, it can be seen in both the Qinghai-Tibet Plateau and the southeast coast. Their external morphology and internal structure are similar to those of xerophytes. Because saline soil causes physiological drought, plants become fleshy and the water content in the body is high, which can reach more than 90% of the body weight. And accumulated a lot of salt, which can reach about 4%, so the osmotic pressure of cell fluid is very high, which can reach 40- 100 atmospheric pressure, and the root system is also very developed, which ensures that plants can absorb enough water from high-salt soil. Excess salt in the body can be excreted through the secretory glands of stems and leaves, which is called salt secretion. Another halophyte grows on the beach in the south of China, forming a beach forest-mangrove, which is composed of mangrove plants (Figure 2), sea lilies, sea lilies and plum trees. The whole factory was submerged by seawater at high tide and exposed to the beach at low tide. They should not only adapt to the salt in seawater and swamp mud, but also resist the impact of tides and waves. In addition to the characteristics of general halophytes, they also produce many columns at the lower part of the trunk, which bend downward into an arch and go deep into the soil, so that the plants are firmly fixed on the mud beach. This root also has the function of breathing. Because there is little air in the swamp soil, the ventilation tissue in the body is quite developed, and the sunken pores and lenticels are helpful for gas exchange inside and outside the body. Some can also produce a respiratory root, which is exposed to the ground for gas exchange. Because of the long-term growth in the environment of tidal fluctuation and seawater impact, it is difficult for seeds to get a stable germination environment, and the propagation mode has also changed. After the seed matures, it does not leave the mother, but develops into a young embryo, and the hypocotyl is thick and rod-shaped. They can absorb a lot of nutrients from their mothers, store them in young embryos, grow to a certain extent, and fall into swamp soil by their own weight. After a few hours, lateral roots will grow from hypocotyls. Some young embryos may be washed away by the sea, and they can grow and develop rapidly as long as they come into contact with the appropriate mud beach. This process is called viviparous phenomenon. Alpine plants in the plateau area, especially the top of the mountain above 4000 meters, have no snow all the year round, and the temperature is extremely low, with the annual average temperature below 0℃; Strong wind, strong ultraviolet rays, thin soil ridges and little water; Just under this snow line, there are still some plants standing proudly on the snow-capped mountains, not afraid of the cold. For example, Saussurea medusa (Figure 3) has a short body, a strongly shortened stem node, and a rosette-like and hemispherical leaf sequence close to the ground, which is conducive to resisting high mountain winds. But also a slightly higher temperature can be obtained from the surface. It can not only prevent colds, reduce water loss, but also reflect too much sunlight, especially ultraviolet rays, so as not to harm tissues in the body. It also has a thick and deep root system that can absorb water and inorganic salts from gravel cracks or poor soil. These morphological characteristics are important weapons for them to overcome the harsh environment, and also the result of long-term adaptation to the environment. Under-forest plants growing under forests are very sensitive to light requirements, because light is covered by trees and shrubs, and the light that can penetrate into forests is extremely rare, but sunlight is indispensable for plant life activities. Herbs under the forest are bound to struggle for their own survival and how to get sunlight, and some species are developing in the direction of liking shade. For example, Rhizoma Arisaematis and Paris polyphylla in France, their leaves become larger and wider, thin and smooth, spread horizontally, and the chloroplast volume increases, which is beneficial to absorb weak sunlight. Other species, they become epiphytes, such as Dendrobium nobile and Cymbidium pendulum (Figure 4), which are attached to the trunk or branches of trees, so that plants can rise to the space where it is easier to get sunlight. You can also see such plants under the forest, and their stems become particularly slender and flexible, such as Rabdosia crassipes, Lithospermum, and snake grapes. They will produce special climbing organs, climb up or wrap their stems around other trees; In this way, its leaves can reach the upper layer of the forest and ensure that it can get the sunshine needed for photosynthesis. This is called vine. Others adapt to the habitat under the forest by shortening the life cycle, such as Anemone of Anemone and Corydalis of Corydalis. In early spring, when deciduous trees and shrubs in the upper layer of the forest have not yet grown leaves, that is, when the sunshine is the most abundant under the forest, they will break through the ground, quickly grow stems and leaves, and soon blossom and bear fruit. In a few short weeks, they will complete their whole life history process. By the time the leaves of trees and shrubs fully grow out and prevent sunlight from penetrating into the forest, they will have completed their life history and sown their seeds. Parasitic plants also have a few plants in the plant kingdom. Like animals, they have no chlorophyll in their bodies, can't carry out photosynthesis, and can't make organic matter by themselves. Instead, they rely on parasites that live on the objects they plant and absorb nutrients from their hosts to nourish themselves. They are called heterotrophic plants or parasitic plants, such as Cassythe filiformis and Cynomorium songaricum, rootless vines of Cuscuta chinensis. Their leaves have degenerated and plants are no longer green. Although other species also have parasitic characteristics, their roots are still inserted into other plants to absorb water and some nutrients from the host, but their leaves are still developing normally, and chlorophyll in cells can still be used for photosynthesis to make organic matter, which is also autotrophic. These plants are called semi-parasitic plants such as Taxilli, which are the representatives of this kind of plants. * * * Plants When we harvest peanuts, soybeans and soybeans, we can often see sandy things in the roots, called nodules, because rhizobia live in root tissues and reproduce in root cells, which makes the tissues there develop abnormally and become nodules. These plants can provide water, inorganic salts and living places for nitrogen-fixing rhizobia, which can fix free nitrogen in the air as an available nitrogen source, not only for nitrogen-fixing rhizobia itself, but also for peanuts or soybeans. These two different plants * * * live together and complement each other, so that they can both benefit from struggle for existence. Because this feature of * * * is conducive to the preservation and development of the race, it has been passed down from generation to generation and developed into a strong team. Leguminous plants and some other plants have the phenomenon of symbiosis with rhizobia. Insect-eating plants seldom notice that plants can also eat animals in our daily life. There are indeed some species in the plant kingdom, which live in a nitrogen-deficient environment for a long time, and it is not enough to rely solely on the roots to absorb nitrogen sources from the soil; Other methods of obtaining nitrogen must be developed. For example, Utricularia aurea (Figure 5) lives in small acidic ponds or ditches, and the living environment forces its plants to mutate. After natural selection and genetic action, some of its leaves developed into a squirrel-cage insect trap; The mouth of the capsule has a door (flap) and hair contact. When the insects swimming in the water touch the hair at the mouth of the bag, the door opens immediately and the insects enter the bag with the water flow. The structure of the door is that they can only get in but not out, and the bugs that enter the bag can't get out anymore. Drowning in the digestive juice in the capsule, because there are many gland cells that can secrete digestive enzymes on the inner wall of the capsule, this enzyme can decompose and digest the protein of worms to supplement the needs of plants for nitrogen. There is also a strange pitcher plant. Its insect trap is like a bottle, which is a metamorphosis of some petioles. The small cover at the mouth of the bag is the leaf itself. The leaves of Drosophila peltata have become insect traps with many glandular hairs. The glandular hairs can secrete enzymes for digesting protein, and transform the protein in insects into the nitrogen it needs.