Figs. 1 - 6. One- and two-year-old peach stems inoculated with L. persoonii. Figs. 1,5,6. Stereomicrographs. Figs. 2 - 4. Light micrographs. Fig. 1. Longitudinal section through pith (P), xylem (X), and bark (B) (tissues are between opposite oriented arrows), sampled seven days after inoculation with Leucostoma persoonii, showing four polysaccharide-rich reaction zones (large arrows). Colonization from left to right had proceeded in the bark through the first zone and was almost to the second. x15. Fig. 2. Longitudinal section of peach bark and vascular cambial (VC) tissues seven days after inoculation with L. persoonii showing hyphal aggregations (H) in periderm and cortex regions and alteration of cambial derivatives (arrow). Colonization proceeding from right to left. x420. Fig. 3. Longitudinal section of peach bark and vascular cambial (VC) tissues seven days after inoculation with L. persoonii showing hyphal aggregation (H) in cortex and alteration of cambial derivatives (arrow). Colonization proceeding from right to left. Note that very little new phloem has been produced. x560. Fig. 4. Inter- and intracellular colonization of phloem tissues by hyphae of L. persoonii (arrows). Colonization proceeding from bottom to top of micrograph. x680. Figs. 5,6. Transverse views of peach stems inoculated with L. persoonii (Fig. 5) or noninfested malt agar (Fig. 6). Stems were excised at the base and immersed in stain solution to demonstrate the location of nonfunctional xylem tissues (light areas, NX). Note location of functional xylem (FX) in the new callus tissue in Fig. 6 versus the regions of nonfunctional xylem in callus tissues in Fig. 5. Pith (P), gum ducts (GD), and xylem barrier zone (BZ) are present. x8. (Fig. 1 from Biggs, 1984).