Development of the Vascular Tissue of the Wheat and Barley Caryopsis as Related to the Rate and Duration of Grain Filling 1

An anatomical study of developing wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.) caryopses was conducted in order to relate the development of the vascular and associated tissues to the rate and duration of grain filling. Caryopsis development of the two species was similar, differing mainly in the timing of events, including the date of flowering and the duration of the grain‐filling period. The main vascular bundle began to differentiate after anthesis and differentiation was completed at about the same time elongation of the kernel ended. The sieve tubes of the main bundle remained open and visually functional until the end of grain filling. The cell walls of the chalaza began to lignify midway through the grain‐filling period, but lignification was not a barrier to grain filling. Yellow or brown‐colored compounds (possibly phenolics) accumulated within the vacuoles of the chalazal cells of barley, but these did not adversely affect the rate of grain filling. In both wheat and barley, the marked decline in the rate of dry matter accumulation occurred prior to the collapse of the phloem and chalaza. Thus, the collapse of these tissues did not trigger events leading to the termination of grain filling. Barley had more sieve tubes than wheat, yet the rate of grain filling was similar for the two species. Thus the number of sieve tubes was not related to the rate of grain filling.