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root cap[′rüt ‚kap]
the protective formation (effective primarily against mechanical damage) on the growing tip of a root.
The root cap is a small (about 0.2 mm, or, rarely, in aerial roots, up to several mm) conical cap covering the tender cells of the root apex and part of the root’s growth zone. It differentiates in the earliest stages of root development from cells composing the calyptrogen (for example, in grasses and other monocotyledons) or from the apical meristem of the root (in many dicotyledons and gymnosperms). The root cap is composed of a complex of living parenchyma cells with thin mucilaginous membranes and mobile starch grains (statoliths) that are important in the geotropical reaction of the root. The outer layers of cells of the cap separate easily, and during friction with soil particles they are sloughed off, easing the root’s passage through the soil. In water plants the root cap may be reduced and be replaced by a root pocket (as in duckweed, frogbit, and water chestnut).
R. P. BARYKINA