The vascular system in the rachis of ears of wheat (Triticum aestivum L. cvs Gamenya, Olympic and Bungulla) was examined on material grown in the field and in a growth cabinet. In the internodes, central and peripheral bundles were observed and their mean number and size were determined. A significant 1: 1 relationship between the number of spikelets on the ear and the number of central bundles at the base of the rachis was established. The number of both central and peripheral bundles declined acropetally along thé length of the rachis. The decline in peripheral bundles occurred mainly between internodes 1 and 6, numbered from the base. The decline in central bundles occurred at a rate of less than one bundle per internode between internodes 1 and 4, though in some ears, there was no decline; in larger ears, central bundles declined at a rate of one to two bundles per internode between internodes 5 and 11. Above internode 11, the rate of decline varied with ear size. Three central bundles consistently reached the terminal spikelet. The number and cross-sectional surface area of xylem vessels and sieve tubes and the total vascular size also declined acropetally along the rachis. The decline in total vascular size was due to (a) some bundles branching and to reductions in size, (b) the diversion or dropping of bundles into spikelets, or (c) a combination of (a) and (b). These observations are discussed in relation to the distribution of grain number and weight on the ear.