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In Ailanthus excelsa ROXB., the gum‐resin duct in the pith of the stem develop schizogenously. It is suggested that dictyosomes are involved in dissolution of the middle lamella of radial walls of epithelial cells by secretion of lytic enzymes into the cell walls. In epithelial cells of young ducts osmiophilic droplets are observed in plastids and mitochondria. Epithelial cells resemble transfer cells in having few wall ingrowths. The cytoplasm of the epithelial cells of active ducts is rich in rough and smooth ER, free ribosomes, polysomes, mitochondria with swollen cristae, plastids with osmiophilic droplets, dictyosomes and vesicles. Upto and through active duct a dense, osmiophilic material is synthesized in plastids and mitochondria, and then appears to be transported through the plasmalemma by granulocrine secretion. Dictyosome‐derived vesicles appear to be involved in the secretion of gum polysaccharides. Epithelial cell walls facing the duct lumen are loose appearance and sloughed off wall material. After the secretory phase, the cytoplasm of the epithelial cell disintegrates.