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(Plantae, or Vegetabilia), organisms characterized by autotrophic nutrition based on the use of solar energy and by the presence in the cells of dense membranes usually consisting of cellulose. Photosynthesis and the physiological and biochemical processes related to photosynthesis permit the unambiguous differentiation of plants from other living organisms. Plant species with heterotrophic nutrition—saprophytes and parasites—are rare, and they are always of secondary origin. Features determined by growth processes and mode of life, such as unusual developmental cycles, methods of organ formation, and attachment to a particular substrate, are not universal in the plant world.
In general, a complex of characteristics makes it easy to distinguish all plants, especially highly organized ones, from representatives of the other kingdoms of living organisms. Only at a lower level of development, especially among unicellular organisms, are the differences somewhat unclear. For this reason it was only in the middle of the 20th century that kingdoms for some groups of organisms, such as flagellates, were defined. However, there are adequate grounds for breaking up the flagellates into forms belonging to either the plant kingdom or the animal kingdom. The slight difficulty in distinguishing between them is evidence of the single origin of the entire organic world, which divided, judging by the paleontological findings, into separate kingdoms probably more than 3 billion years ago.
Bacteria, blue-green algae, and fungi have often been traditionally assigned to the plant kingdom. However, research conducted in the mid-20th century supports the long-held doubts as to whether these organisms are actually plants. Bacteria and blue-green algae do not have a true nucleus with a nuclear membrane and nucleolus; in addition, they lack the type of sexual process characteristic of other plants. These and other traits sharply distinguish bacteria and blue-green algae both from true plants and from other forms of living organisms. Hence, they are now assigned to the special superkingdom Prokariota.
Although fungi have a nucleus, other characteristics of their morphology and chemistry sharply distinguish them from true plants and living organisms of the other kingdoms. Their membrane is usually chitinous rather than cellulosic, and their mode of feeding is heterotrophic. Fungi are now assigned to a special kingdom, Mycetalia, or Fungi, and are grouped together with plants and animals into the superkingdom Eukariota.
Unicellular plants are characterized by elements inherent in any organism, but they differ from other unicellular organisms in that they have chloroplasts and some ultrastructures. Usually their membrane structure is distinctive, and their vacuoles are developed. As the level of organization rises, the differences between plants and representatives of the other kingdoms become so apparent that multicellular plants can be unfailingly distinguished, even by external appearance, from representatives of other kingdoms of the organic world.
A very important morphological characteristic of plants is the marked segmentation of the body, which results in an increase in surface area owing to the mode of nutrition —absorption of gases and liquids (air and water with dissolved nutrients) from the external environment. In higher plants, the segmentation and differentiation of the body result in the formation of a large number of specialized structures and organs. Many important characteristics of the external and internal morphology of plants are determined by the nature of their growth and reproduction.
The plant kingdom embraces three main taxa (subkingdoms, or phyla): red algae (Rhodobionta), true algae (Phycobionta), and higher plants (Embryobionta). The subkingdoms include more than 350,000 species of great diversity.
Many generations of botanists have sought to identify the principal features in the formation and development of individual plant structures and organs and of plants in general. They have studied a range of plants, from microscopic unicellular algae to flowering plants whose physiological and biochemical processes and morphological formations are marked by a high level of development. The modern theory of evolution is the basis for understanding the plant world as a whole over both time and space. The related evolution of the plant world and the animal world (especially insects, birds, and mammals) is confirmed by data on evolution.
The existence of an animal world—inclusive of man—would be impossible without plants, because they play a special role in the life of our planet. Of all the living organisms, only plants are capable of storing solar energy and using it to create organic matter from inorganic substances. Plants extract CO2 from the atmosphere and release O2. It was the activity of plants that led to the creation of an atmosphere containing O2, and it is plants that keep the atmosphere suitable for breathing.
Plants are the vital link in the complex food chain of all heterotrophic organisms, including man. Terrestrial species form steppes, meadows, forests, and other plant communities, creating the topographical diversity of the earth and providing an infinite variety of ecological niches for organisms of all the kingdoms. The origin of soils was a direct result of plant life, and plants continue to play a major role in soil formation.
Of the many different species in the plant kingdom, seed plants, especially flowering ones (angiosperms), are of special importance to man. Seed plants include almost all cultivated species. Of particular importance to man are cereal crops (wheat, rice, corn, millet, sorghum, barley, rye, oats, and buckwheat). Potatoes form a major part of the diet in countries with a temperate climate, and sweet potatoes, yams, okra, and taro are staples in the more southern regions. Protein-rich legumes (kidney peas, chick-peas, lentils) and other vegetable crops, sugar-yielding plants (sugar beets and sugarcane), numerous oil-bearing plants (sunflowers, peanuts, olives), fruit crops and berry crops constitute an important part of man’s diet. Cotton, flax, hemp, ramie, jute, ambary, sisal, and many other fiber crops are used in the manufacture of clothing and industrial fabrics.
It is hard to conceive of modern society without plants that yield tea, coffee, cacao, grapes (the basis of wine-making), or tobacco. Livestock raising is based on the use of wild and cultivated forage plants, and a vast quantity of wood is required every year as building material and as a source of cellulose. Coal and peat, which can be said to be the sun’s energy stored in plant residues of the past, are among man’s principal sources of energy, and natural rubber extracted from plants has not lost its economic value. The valuable resins, gums, essential oils, dyes, and other products obtained from plants are of major economic importance. Many plants are the principal sources of vitamins, and others (foxglove, rauwolfia, aloe, belladonna, pilocarpus, valerian, and hundreds of others) are sources of important drugs and preparations. Vegetation not only provides the atmosphere with oxygen but also shelters many animals and, in general, creates a situation favorable for the life of all organisms on earth.
In the course of many centuries, man learned how to cover vast areas with vegetation (fields, meadows, wooded parks, gardens, parks) and to select and breed numerous plant forms to meet various special requirements. However, man’s extremely intensive and far from rational activity has resulted in destruction of the vegetation over vast areas and has threatened the extinction of many plant species. The plant world is gradually being protected by special legislation passed in the USSR and some other countries. Botany and many special botanical disciplines are engaged in the study of plant life.
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M. E. KIRPICHNIKOV
What does it mean when you dream about plants?
For a person devoted to gardening, plants can have a wide range of meanings. More specifically, most of us associate plants with life and especially with growth, so a dream about plants could be drawing on either of those associations. Planting has other associations, such as beginning a new project.