Morphological observation on development of juvenile seedlings of Monochoria vaginalis establishing on a flooded paddy soil surface

The development of juvenile seedlings of Monochoria vaginalis (Burm.f.) Kunth var. vaginalis concerning its hypocotyl hairs was investigated morphologically at establishing on 1 mm flooded paddy soil surface and in distilled water. Prime germination of M. vaginalis seeds sown after breaking dormancy was found on a flooded paddy soil surface and in distilled water at 6 h after seeding (HAS). Elongation of cotyledons and hypocotyl hairs of juvenile seedlings appeared at 12 HAS on a paddy soil surface, while lengths of hypocotyl hairs were almost the same as longitudinal length of seeds and cotyledons formed arch on the soil surface at 18 HAS. Seminal roots began to emerge and seedlings adhered completely to the soil surface by hypocotyl hairs, which were longer in length than seminal roots at 24 HAS. At 36 HAS, seed chaffs completely separated from the soil surface, as cotyledons had elongated from standing up, and lengths of seminal roots became longer than those of hypocotyl hairs. Emergence of first leaves and crown roots was simultaneously observed at 48 HAS. Elongations of cotyledons, seminal roots and hypocotyl hairs were completely terminated at 96, 120 HAS and 120 HAS respectively, and the elongation of 2 to 4 crown roots was observed at 120 HAS. Almost half the number of hypocotyl hairs putrefied at 240 HAS. In distilled water, hypocotyl hairs elongated to their longest at 36 HAS earlier than those on a paddy soil surface. It was concluded that hypocotyl hairs supported a strongly physical mechanism in establishing M. vaginalis seedlings on a paddy soil surface.