Hypocotyl-hook translucency of mungbean sprouts is due to calcium deficiency in the hook region of the hypocotyl. The disorder was not associated with any pathogenic organism, and the addition of calcium to the irrigation water at concentrations of 50 or more mg calcium/liter overcame the disorder. Apparently, the supply of calcium in the seed either is not sufficient to maintain the rapid growth of sprouts in the dark, or the calcium cannot be translocated to the hypocotyl hook as rapidly as it is needed;The growth of the mungbean sprouts followed a typical sigmoid pattern, but the growth rate of each organ of the seedling is not synchronous. Growth in terms of an increase in hypocotyl diameter or fresh weight occurs at about the same time, the first 30 to 36 hours after sowing. The maximum growth in length of the hypocotyl and the root occurred at about 55 to 80 and 36 hours after sowing, respectively. The maximum respiratory rate coincided with beginning of the period of maximum growth in length of the hypocotyl;Mungbean sprouts produced ethylene (C(,2)H(,4)) endogenously. When this endogenously produced C(,2)H(,4) was allowed to accumulate in the growing environment, the sprouts exhibited the typical increase in hypocotyl diameter in response to C(,2)H(,4), Accumulation of endogenously produced carbon dioxide (CO(,2)) yielded sprouts with characteristics similar to those produced in an environment where C(,2)H(,4) is allowed to accumulate;A flow-through, controlled-atmosphere system containing 5 to 10% CO(,2) in combination with 10 to 15% oxygen with the balance as nitrogen produced sprouts similar to those grown in air containing 5.0 (mu)liter C(,2)H(,4)/liter. Mungbean sprout quality could be improved by the addition of 5.0 (mu)liter C(,2)H(,4)/liter into the air-based atmosphere in which the sprouts are growing.