Anatomical insights into the vascular lay-out of the barley rachis: implications for transport and spikelet connection.

The rachis vasculature is the result of a two-step process involving an initial layoutfollowed by size adjustment according to floret fertility/spike size. The restriction of large mature vessels to the periphery and that of small immature vessels to the center of the rachis suggests that long distance transport and local supply to spikelets are spatially separated processes.The identification of spikelet-derived veins entering the rachis without fusing with its vasculature indicates that a vascular continuity between rachis and spikelets may be non-essential.