The well-documented inhibition of germinating cotton (Gossypium hirsutum L.) seeds by suboptimal [nonfreezing] temperatures was also observed in the growth of fully autotrophic seedlings. When seedlings of the G. hirsutum varieties, Coker 315, Deltapine 61, and Paymaster 145, were grown at sub-optimal [10-25 C], temperatures for eight days after a two-day period of pre-germination at 31 C in the dark, highly significant varietal differences were seen in the magnitudes of root and shoot growth reductions and in root and shoot water status ratios. Significant differences between varieties were also seen in capacities for growth resumption and, particularly, for regaining unstressed root and shoot water status after the seedlings were returned to 30 C, the optimum temperature for root growth in all three cultivars examined. In a new application, differential scanning calorimetry was used to examine the effects of suboptimal temperatures on the metabolic rates of cotton seedling root tips. Changes in rates and levels of root-tip metabolic heat evolution resulted from in planta and in vitro suboptimal temperature stress and were detectable with this technique.