Histological analysis of embryogenic/organogenic callus of V. planifolia on A4 medium and A10 medium 15 days after subculture. Four-micrometer-thick sections of callus were stained with Periodic acid and Schiff' reagent. a-b. Fifteen-day-old calli on A4 medium (a) and A10 medium (b) respectively CA4 d15 and CA10 d15. Calli inner region containing both small meristematic cells with highly-stained nucleus in mitotic cells zone (MCZ) and vacuolated large cells; arrow indicate multiple MCZ; bar = 100 μm. c-d. Higher magnification of the MCZ in CA4 d15 callus: c, and in CA10 d15 callus: d; arrow indicate accumulation of soluble carbohydrate (sucrose and/or glucose); in d arrow indicates 4 thick-walled proembryonic cells; bar = 50 μm.