The present study was undertaken to make clear the effect of the CO_2 concentration during precooling on the time of flowering and the quality of cut flower in tulips, cv. 'Apeldoorn' and 'Cassini'. The outline of experimental designs is shown in Figs. 1 and 2.
1. When the bulbs of aged flower bud were used, the concentration of CO_2 in the inside atmosphere of desiccator reached 4% or so at the end of each 'a week' treatment and reached more than 11% at that of '3 weeks' treatment. The concentration of CO_2 evolved from the bulbs of younger flower bud was ranged from 1/2 to 1/5 of that evolved from the bulbs of aged one in each set of the corresponding treatments.
2. The nose growth of bulbs kept in a desiccator for the late or entire period of precooling was strongly retarded presumably due to the high concentration of evolved CO_2. However, the result of forcing showed that the shorter the nose length at the termination of precooling was, the earlier the flowering time became.
3. The quality of cut flower tended to be lowered in inverse proportion to the concentration of CO_2 at the end of each treatment.