The aim of this study was to determine the cardinal temperatures for germinating colubrina seeds, verify isothermal velocity variation based on the transition state model and calculate the ΔH≠ variation as a function of temperature. Seeds were incubated at constant temperatures of 5, 10, 15, 20, 25, 30, 35 and 40 oC and alternating temperature from 20-30 oC in an 8-hour photoperiod. The variables analyzed were: G, PC, IVG, TMG, VMG, Fi, U, Z, CR, CPA, MSR and MSP. Arrhenius equation was

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... ed by logarithmic transformation, producing the graph of -RlnV × 1/T from the experimental values of velocity. A net enthalpy change (Delta H≠) in relation to temperature was represented by the expression: Delta H≠ = [RT(Theta – T) × (Tm + TM)]/[(T – Tm) × (TM – T)]. The logarithm regression of the reaction rate on the reciprocal of the temperature fit best to the quadratic model. The distribution of Delta H≠ with asymptotes close to Tm and TM indicated that the processes that occurred in the supra-optimal temperature range were of a different nature from those that occurred in the infra-optimal temperature range. The data showed |Delta H≠| < 12 Kcal/mol in the optimal range and |Delta H≠| > 30 Kcal/mol for temperatures of 10, 15 and 35 oC. The minimum and maximum temperature limits were 10 and 35 oC, respectively. Germination speed was related to temperature in a curvilinear manner. The germination process was endergonic and only occurred when energy was ≥ -38.35 Kcal/mol and ≤ 32.42 Kcal/mol.