Crystals are of common occurrence in plant tissues and considered to be waste products resulting from active metabolism of plant cells. They mostly occur in ray and vertical parenchyma of wood and bark of angiosperm trees and often develop in tissues which soon cease to be functional. While studying the annual rhythm of cambial activity in two species of theVerbenaceae, Tectona grandis (Rao andDave 1981) andGmelina arborea (Dave andRao 1982), crystals of calcium oxalate have been observed in ray initials (Figs. 1–10). The crystals were identified as calcium oxalate after a convincing chemical behaviour towards dilute (10%) acetic, hydrochloric, and sulphuric acids. They appear colorless when viewed with brightfield illumination (Fig. 3), and show birefringence in polarized light (Figs. 1 and 6). Radial, tangential, and transverse sections of 10–15 μm thick were used to study the crystals in polarized light with a Carl Zeiss Axiomat microscope.