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the organ of hydrostatic equilibrium in the colonial Siphonophora. The pneumatophore is located on the upper end of the common trunk of the colony. Its cavity is divided into air-bearing and glandular areas. The cells of the glandular area excrete a gas that is similar in composition to air.
a terrestrial ventilative or respiratory root of some tropical woody plants. Pneumatophores characterize many trees that form mangrove forests, some palms, and the American bald cypress. Such plants grow on swampy soils with a poor oxygen content or along seashores that are flooded when the tide is in. Pneumatophores develop from subterranean roots or rhizomes and grow vertically, rising above the water or soil. Their biological significance is mainly their supply of air to subterranean organs. This is promoted by the anatomic structure of pneumatophores: their thin bark, numerous lenticels, and system of air-bearing intercellular spaces. An abundance of intercellular space often is responsible for the white color of pneumatophores. Plants that usually have pneumatophores do not form them when grown on soils that are not swampy. Thus, pneumatophores are absent in the bald cypress that is raised as an ornamental on the southern coast of the Crimea, in the Caucasus, and in Middle Asia.