The effects of treatment with acid and aluminum on Quercus acutissima seedlings were assessed by measuring growth of shoots, elongation of roots, microscopic observation of root cells, and analysis of cytokinin and cytokinin-like substances involved in cell division. The dry weight of leaves and stems treated with 2.7 mM Al was significantly less than control. However, taproots of seedlings given 2.7 mM Al elongated for 31 cm, whereas those were only 8.5 cm in control plants. The number of xylem and phloem cells increased, as did the number of transverse cortex cells after treatment with 2.7 mM Al. Cortex cell diameter and length and cortex width also increased as a result of the 2.7 mM Al treatment, as did root diameter and width of xylem and phloem.