Seeds from ten provenances of Cedrus libani were subjected to germination test on filter paper saturated with polyethylene glycol (PEG 6000) solutions made up to provide osmotic potentials of 0, -2, -4 and -6 bars. Mean germination percent for all provenances decreased about 48% in -2 bars, 61% in -4 bars and 75% in -6 bars treatments compared to control (0 bar) treatment. There were significant differences among the relative germination percent of the provenances in different treatments. In spite of climatic data, strong correlations were found between germination capabilities under different stress levels and the ecological conditions in the natural habitats of the provenances. Differences between the germination capabilities of the provenances under different stress conditions were interpreted as an intraspesific heritable variation constituted by natural selection.