Vascular Occlusions in the Stem of Ailanthus excelsa Roxb.

The stem of Ailanthus excelsa Roxb. (Simaroubaceae) may developvascular occlusions and gum-resin cavities in the xylem as aresponse to injury and infection. Fungal hyphae are observedin the vessel lumen and in the adjacent parenchyma cells. Theocclusions appeared in various forms and showed varying chemicalcomposition. The chemical nature of the occluding material differedfrom that of the exudate formed in the cavities. The majorityof occlusions contained lipids, protein, polysaccharides, phenolics,lignin and probably pectin, whereas, the exudate contained lipids,protein and four soluble sugars. All the components of the occlusionexcept lignin and pectin appear to have been formed in the parenchymacells adjacent to the vessel and migrated to vessel lumen throughthe vessel wall pits. The different constituents migrate intothe vessel lumen independently where they mix to form occlusions. Ailanthus excelsa Roxb., vascular occlusions, lignin, fluorescence, exudation