Lotus (Nelumbo nucifera) has been cultivated as an ornamental and food plant in Japan for more than 1000 years. As large areas are required for its cultivation (approximately 2 m2 per plant), physiological research, such as into the effect of environmental factors on dormancy, has not been well studied until recently. In this paper, seedlings were used to examine environmental factors affecting dormancy induction.In a first experiment, seeds were sown from 6 April to 6 October at 2-month intervals, and cultivated for 2 months in an unheated greenhouse. In a second experiment, seeds were prepared for germination on 16 November and 16 May and the seedlings were grown at 25 or 30 degrees C under natural daylength in phytotron growth rooms. After 1 month, the seedlings were cultivated at 20, 25 or 30 degrees C for a further month. The number of leaves and rhizome branches on the main stem were counted, and growth of rhizomes on the main stem was calculated using a rhizome enlargement index (= maximum internode diameter/internode length) after 2 months of culture in both experiments.Rhizomes elongated without enlargement when the seeds were sown in April and June. Sowing the seeds in August and October resulted in rhizome enlargement from the tenth and fifth internodes, respectively. Rhizomes enlarged in the November-sowing but elongated in the May-sowing irrespective of temperature treatments under natural daylength in the phytotron rooms. The seedlings cultivated from May at 25-30 degrees C for 2 months had more leaves, and more rhizome branches and nodes than those cultivated from November.Short days led to induced dormancy in lotus.