Changes in the fresh and dry weights of the component parts of plants of tulip cv. ‘Apeldoorn’ were followed in bulbs kept at low and high temperatures (9 and 18°C respectively) from the time of completion of flower differentiation until anthesis. There were marked differences between shoot dry weights at the two temperatures. At 9°C the stem, leaves and flower grew exponentially throughout the whole period, but at 18°C the specific growth rate of the stem and leaves declined throughout the period of the experiment. At 9°C the proportion of total dry weight in shoots and daughter bulbs was higher than at 18°C, and the proportion in the mother bulb was correspondingly smaller. At both temperatures the fresh weight dry weight ratios of the mother bulb, shoot and daughter bulbs declined during dry storage, the decline being greater at 9°C. After planting, the ratio for all plant parts increased at 9°C, but scarcely changed at 18°C. These results are discussed in relation to dormancy, to the low-temperature requirement for successful and rapid flowering and to flower quality.