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plants in dry environments, adapted to withstand heat and drought by means of a number of structural mechanisms. Xerophytes have various ecological and physiological characteristics.
One group of xerophytes, the succulents, has fleshy leaves (agave and aloe) or stems (cacti) and a surface root system. They resist heat, owing to the high viscosity of their protoplasm and the high content of stored water in their cells, but they cannot withstand drought. Another type of xerophyte, the hemixero-phyte, has a root system that reaches ground water. Unable to survive prolonged dehydration of tissues, plants of this type are resistant to droughts, owing to their uninterrupted water supply and intensive transpiration and metabolism. Xerophytes with root systems reaching ground water that grow in the steppes, such as sage, are not able to withstand great heat; those that grow in deserts, such as camel thorn, are heat-tolerant.
Other xerophytes, the euxęrophytes, have a branched but shallow root system (not deeper than 50–60 cm). These plants, which include certain species of wormwood, are pubescent; because their protoplasm is highly elastic and viscous and their metabolism slow, they withstand dehydration and heat well. Another group of xerophytes, the poikiloxerophytes, experiences anabiosis during dehydration, a state in which a plant’s water content is only 2–5 percent and its protoplasm acquires a gelatinous consistency. However, owing to the preservation of balanced respirative activity, the cell organization does not break down to the point of almost complete dehydration. Sometimes other groups of xerophytes are distinguished.
P. A. GENKEL’