Vascular tissue in blr , bp and rev mutant combinations. Toluidine blue stained sections from inflorescence stem vascular tissue adjacent to the first cauline leaf. (A) Wild type vascular bundle with arrowheads pointing to a xylem vessel (xv), xylary fibres (xf) and vascular meristem (procambium; pc). (B) bp mutants are indistinguishable from wild type, except in differentiation defective stripes (bp*) where the arc of procambium cells is flattened, xylem vessels are absent or reduced in size and many cells are small and darkly stained suggesting they lack secondary walls (green in wild type xylem; A). blr (C) and blr rev (E) vascular tissue in which the arc of procambium is flattened and xylem vessels appear absent. (D) rev. (F) Large vascular expansion in blr bp. In vascular tissue derived early in development (square bracket; e) all cells are small and many lack secondary walls. In contrast, later derived tissue (square bracket; l) contains differentiated xyary fibres but no vessels, except in differentiation defective regions of the stem (blr bp*) where very few cells with secondary wall are present. (G) bp rev double mutants are indistinguishable from rev in most regions of the stem, however, in differentiation defective regions (bp rev*) cells were smaller than those observed in bp*. (H) Cells in blr bp rev inflorescence stems were extremely small and in the vast majority of cases secondary walls appeared absent. Scales are 50 μm.