PLANT

(kingdom Plantae), multicellular, eukaryotic life form fundamentally characterized by (1) an almost exclusively photosynthetic mode of nutrition, in which the plant produces chemical energy (in the form of sugars) from water, minerals, and carbon dioxide with the aid of pigments and the radiant energy of the Sun, (2) essentially unlimited growth at localized regions of cell divisions called meristems, (3) cells that contain cellulose in their walls and are therefore more or less rigid, (4) the absence of organs of locomotion, resulting in a more or less stationary existence, (5) the absence of sensory and nervous systems, and (6) life histories that show an alteration of haploid and diploid generations (the dominance of one over the other is taxonomically significant). No definition of the kingdom completely excludes all nonplant organisms or even includes all plants. There are many plants, for example, that are not green and do not produce their own food by photosynthesis but are parasitic on other living plants; others are saprophytic, obtaining their food from dead organic matter. Many animals possess plantlike characteristics, such as the lack of mobility (e.g., sponges) or the presence of a plantlike growth form (e.g., some corals and bryozoans), but in general such animals lack the other characteristics of plants cited earlier and, therefore, cause little confusion. In the past, classification systems have been devised that place such difficult groups as protozoans, bacteria, algae, slime molds, and fungi in the plant kingdom, but morphological and physiological differences between these organisms and plants have caused most scientists to classify them outside the plant kingdom. Plants are treated in a number of articles. For a basic description and analysis, see plant. For descriptions of the various classes and orders of plants, see angiosperm; bryophyte; gymnosperm; lower vascular plant; tree. For discussions of plants in relation to the biosphere, see biosphere; development; growth; photosynthesis. For the study of plants, see botany. See also agriculture, history of; agricultural economics; agricultural technology; gardening; horticulture. any member of the kingdom Plantae, multicellular, eukaryotic life forms characterized by (1) photosynthetic nutrition, in which chemical energy is produced from water, minerals, and carbon dioxide with the aid of pigments and the radiant energy of the Sun, (2) essentially unlimited growth at localized regions, (3) cells that contain cellulose in their walls and are therefore to some extent rigid, (4) the absence of organs of locomotion, resulting in a more or less stationary existence, (5) the absence of sensory and nervous systems, and (6) life histories that show an alteration of haploid and diploid generations, with the dominance of one over the other being taxonomically significant. No definition of the kingdom completely excludes all nonplant organisms or even includes all plants. There are plants, for example, that do not produce their food by photosynthesis but rather are parasitic on other living plants; other plants are saprophytic, obtaining their food from dead organic matter. Some animals possess plantlike characteristics, such as the lack of mobility (e.g., sponges) or the presence of a plantlike growth form (e.g., some corals and bryozoans), but in general such animals lack the other characteristics of plants cited here. In the past, systems have been devised that classified such groups as protozoans, bacteria, algae, slime molds, and fungi as plants, but morphological and physiological differences between these organisms and plants have led most scientists now to classify them outside the plant kingdom. Additional reading General surveys providing definitions of the kingdom and characterizations of major groups of plants include Peter H. Raven, Ray F. Evert, and Susan E. Eichhorn, Biology of Plants, 4th ed. (1986), an excellent introductory text; Harold C. Bold, Constantine J. Alexopoulos, and Theodore Delevoryas, Morphology of Plants and Fungi, 5th ed. (1987), a detailed and comprehensive treatment that includes algae and fungi; Ernest M. Gifford and Adriance S. Foster, Morphology and Evolution of Vascular Plants, 3rd ed. (1989), an advanced text; and V.H. Heywood et al. (eds.), Flowering Plants of the World (1978, reissued 1985), a beautifully illustrated guide. Henry S. Conard, How to Know the Mosses and Liverworts, 2nd ed., rev. by Paul L. Redfearn, Jr. (1979); and W.B. Schofield, Introduction to Bryology (1985), are well-illustrated guides to the bryophytes. John T. Mickel, How to Know the Ferns and Fern Allies (1979), is an introduction to the ferns and lower vascular plants of the United States.Plant physiology is the subject of many specialized studies. T. Wallace, Trace Elements in Plant Physiology (1950), is the classic exposition of the pioneering experimentation on and founding principles of the subject. Emanuel Epstein, Mineral Nutrition of Plants: Principles and Perspectives (1972), treats the subject from the perspective of the basic and applied plant sciences; John Skujins, Essential Nutrient Elements and Nutrient Cycles in Soil, pp. 4148 in vol. 3 of David W. Newman and Kenneth G. Wilson (eds.), Models in Plant Physiology and Biochemistry, 3 vol. (1987), offers a concise overview of the subject; A.D.M. Glass, Plant Nutrition: An Introduction to Current Concepts (1989), provides a complete exposition suitable for the informed general reader; and A. Luchli and R.L. Bieleski (eds.), Inorganic Plant Nutrition (1983), is a definitive advanced treatment of mineral nutrition. Metabolic cycles and photosynthesis in plants are studied in Cecie Starr and Ralph Taggart, Biology: The Unity and Diversity of Life, 5th ed. (1989); David D. Davies (ed.), Metabolism and Respiration (1980), Biochemistry and Metabolism (1987), and Physiology of Metabolism (1987); G. Ray Noggle and George J. Fritz, Introductory Plant Physiology, 2nd ed. (1983), which provides an overview of plant metabolism; and Frank B. Salisbury and Cleon W. Ross, Plant Physiology, 3rd ed. (1985), which offers a more advanced treatment. Annual Review of Plant Physiology and Plant Molecular Biology covers current research in all subjects of plant physiology.Ecological considerations are discussed in Michael G. Barbour, Jack H. Burk, and Wanna D. Pitts, Terrestrial Plant Ecology, 2nd ed. (1987); Victor V. Rendig and Howard M. Taylor, Principles of Soil-Plant Interrelationships (1989); Friedrich G. Barth, Insects and Flowers: The Biology of a Partnership (1985; originally published in German, 1982); and Oswald Tippo and William Louis Stern, Humanistic Botany (1977), on the impact of plants on human beings. On the cultivation of plants, see N.I. Vavilov, The Origin, Variation, Immunity, and Breeding of Cultivated Plants: Selected Writings, trans. from Russian (1951); and R. Walden, Genetic Transformation in Plants (1989).Analyses of evolutionary relationships are provided in Barry A. Thomas, The Evolution of Plants and Flowers (1981), a spectacularly illustrated introduction; William G. Chaloner, Early Land Plants: The Saga of a Great Conquest, pp. 301316 in Werner Greuter and Brigitte Zimmer (eds.), Proceedings of the XIV International Botanical Congress (1988), a summary of what is known about the earliest land plants; Wilson N. Stewart, Paleobotany and the Evolution of Plants (1983), on the fossil history and the evolution of plant structures; and Else Marie Friis, William G. Chaloner, and Peter R. Crane (eds.), The Origins of Angiosperms and Their Biological Consequences (1987), a collection of writings on the geography, climate, ecology, plant-animal interactions, structure, reproductive biology, and interrelationships of flowering plants in their evolution from the Cretaceous to the modern biota.For classification, see Lynn Margulis and Karlene V. Schwartz, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, 2nd ed. (1988), a brief account of the diversity and important traits of the major groups of living organisms according to the five-kingdom system of classification; Albert E. Radford et al., Vascular Plant Systematics (1974), a comprehensive sourcebook on all areas of higher plant systematics and a complete survey of terminology; and Arthur Cronquist, An Integrated System of Classification of Flowering Plants (1981), a scholarly outline of the modern system of angiosperm classification based on available information. William C. Dickison Rudolf Schmid John H. Yopp George M. Woodwell Gar W. Rothwell