Thermostability of root cell membranes of excised roots of 'Grande Naine' banana, 'Carrizo' citrange, Ixora coccinea and Dracaena marginata 'Tricolor' were determined utilizing electrolyte leakage techniques. Mathematical models were developed to predict interaction of temperature (25 to 60 C) and exposure time (30 to 300 min.) on root membrance injury. Predicted critical exposure durations at 50 C were 45, 105, 221 and 221 min. for citrus, banana, ixora and dracaena, respectively. The physiological response to root temperature of 28°, 34° and 40°C for 6 hours daily differed with plant genera, although 34°C appeared to be the optimum or maximum allowable temperature in this study. Shoot to root ratio was highest at the 40 °c root temperature for ixora, citrus and dracaena and was the lowest at 40°C for banana. ----- La termostabilidad de membranas de celulas radiculares de raices cortados de banano 'Grande Naine', citrange 'Carrizo', Ixora coccinee y Dracaena marginata 'Tricolor' fue determinado usando tecinas de goteo electrolirico. Se desarrollo modelos matematicos para predicar interaccion de temperatura (25 ° a 60°C) y tiempo de exposicion (30 a 300 minutos) sobre dafio a Ia membrana radicular. Duraciones predicados de exposlcion cri'tico a 50°C eran 45, 105. 221 y 221 minutos para ci'frico, banano, ixora y dracaena, respectiveamente. La reacckin fisiol6gica con temperaturas radiculares de 28°, 34° y 40°C por 6 horas diario varid entre genero, pero 34°C parecid'ser la temperatura d'ptima 0 maxima permisible en este estudio, La relacidn del tallo a raa era la mas alta con una temperatura radicular de 40°C para ixors, citrico f. dracaena y era la mas baja a 40°C para banano.