Through the thermodynamic relationships inherent in plant metabolism, growth temperature affects the fundamental interactions of metabolic factors such as water and mineral nutrients, thus altering growth and development. In comparison to 30 C, temperatures of 10,15,20,25 and 35 C, decreased, to varying degrees, root and shoot elongation of 10-day old seedlings of three commercial cotton (Gossypium hirsutum) varieties. Dry cand fresh weight accumulation were also affected significantly in these photosynthetic seedlings. Further, non-optimal temperatures altered root and shoot water status[relative water contents]. When seedlings which had been exposed to non-optimal temperatures from Day 4 through Day 8 were grown on Day 9 and 10 at 30 C, distinct differences were observed in varietal capacities for returning to unstressed water status and resuming normal growth. Exogenous calcium (0.1, 1.0, or 10mM) was found to protect seedlings of all three varieties from non-optimal temperature stress and/or to increase recovery capacity, depending on the sensitivity of a variety to non-optimal temperatures.