Cramb is an important medicinal and industrial plant which distribute in a vast area of Khorasan Razvi rangeland. A laboratory study was conducted to investigate the effect of different temperatures on seed germination of Crambe kotschyana in a randomized design with four replications of 25 seeds. Various constant temperatures (2, 5, 10, 15, 20, 25, 30, 35 and 40ºC) were considered. The characteristics such as percentage of seed germination, rate of seed germination, the time of reaching 50% seed germination were recorded. The effect of temperature on rate and percentage of germination was significant. Maximum seed germination (100%) occurred in all temperatures except 2, 35 and 40ºC. In All temperatures except of 2, 35 and 40ºC, there was no significant difference in rate of seed germination. However, the highest rate of seed germination was obtained in 20 ºC. Based on linear regression between germination rate and temperature in both species, the cardinal temperatures: minimum (Tmin), optimum (To) and maximum (Tmax) were determined which were: 1.7, 18 and 43 ºC for Crambe abyssinsca, respectively.
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