Intercellular Spaces

cavities in plant tissues that are filled with air or with the secretions of surrounding cells, such as resins, essential oils, or mucus.

Based on the mode of formation, three types of intercellular spaces are distinguished. Schizogenous intercellular spaces arise as a result of the separation of neighboring cells during growth and differentiation. Often the walls separate only at the junctions at which several cells meet, and, as a result, small intercellular spaces are formed, having three or four angles in cross section and resembling narrow canals when seen in longitudinal section. As the cells separate farther, the spaces enlarge, forming stomatal apertures, the air-bearing canals in aquatic plants, the resin canals in the Coniferae, and the secretory ducts in the Compositae and Umbelliferae.

Rhexigenic intercellular spaces result from the rupture, or rhexis, and subsequent atrophy of cells. The large cavities in the internodes of stems in many Gramineae and Labiatae are formed by cellular rhexis. Lysigenous spaces, for example, the secretory cavities in the leaves of Eucalyptus and Dictamnus and in the outer layer of the pericarp of Citrus, result from the dissolution of a group of cells. Sometimes intercellular spaces of mixed origin develop, which, having been formed schizogenously, enlarge rhexigenically or lysigenously.