The Role of the Oxygen Permeability of the Seed Coat in the Dormancy of Seed of Xanthium pennsylvanicum Wallr

A method for direct identification and quantitative measurementsof mixed or pure gases diffusing through seed coats was devisedto test the hypothesis that the dormancy of Xanthium pennsylvanicumseeds is caused by oxygen-impermeable seed coats. The diffusionof oxygen through seed coats of X. pennsylvanicum was shownto obey Fick's first law. Oxygen diffused through the lowerand upper seed coats at the same rate. Imbibed lower and upperseeds showed essentially equal oxygen uptake rates before radicleemergence. This uptake was lower than the rate at which oxygencan diffuse into the seed. Therefore upper seeds are not dormantbecause of seed coat restriction of oxygen diffusion. The relationshipsof oxygen with other factors involved in seed dormancy are discussed.