Tuber formation in potatoes was studied in an in vitro model system, using single-node cuttings from short-day grown plants (Hendriks el al. 1991, Plant Mol. Biol. 17: 385-394). The levels of anions, including chloride, nitrate, phosphate, malate, oxalate and citrate, were determined using high pH anion chromatography, with ion-suppressed conductivity detection. Determinations were done using very small tissue samples (<5 mg fresh weight). Visible swelling of the buds started at day 5, and all buds formed tubers within 48 hours.