Vascular system of the fertile spikelet of Sorghum (Gramineae: Panicoideae)

Abstract

The vascular system of the sessile, fertile spikelet of Sorghum was reconstructed from serial transverse sections. The vascular system is a composite of the basipetal extensions of the traces from the appendages on the rachilla. The rachilla immediately above the glumes consists of an outer and an inner series of these vascular extensions. The basipetal continuations of the median traces of the sterile and fertile lemmas, and of the traces from the stamens comprise the inner series. The outer series consists of the continuations of the many lodicule traces and of vascular bundles descending from the posterior of the pistil. The component of the vascular system related to the pistil is a plexus of xylem and phloem in the form of a hollow cylinder traversed by a large vascular bundle that is the basipetal continuation of the stylar bundles. Bundles from the anterior of the pistil merge with the hollow cylinder at its anterior. Several collateral bundles from the placenta merge with the hollow cylinder at its posterior. Distal portions of these placental bundles supply the short chalaza of the ovule but do not enter it. The vascular system of the fertile spikelet of Sorghum is typical of the Panicoideae, and is useful in distinguishing the Panicoideae from the other subfamilies of grasses. Key words: Sorghum, spikelet, floret, vascular system.