The effect of nearly constant water potential on germination of citrus, sunflower, and lettuce seeds was studied. Water potential equilibration was achieved by placing soil above a cellulose acetate membrane which was in contact with a solution of polyethylene glycol-6000. Selection of solute potentials in the solution resulted in controlled water potentials in the soil over a range of 0 to minus;14.9 bars for citrus and 0 to minus;8.0 bars for sunflower and lettuce. The water stress experienced by germinating seeds in this system is largely the result of a matric effect rather than a solute effect.Citrus seeds germinated at water potentials as low as minus;4.7 bars and lettuce at minus;4.1 bars, but sunflower germinated at minus;8.0 bars. Sunflower germinated as rapidly at minus;4.1 bars as lettuce at minus;2.3 bars, both reaching 50 germination at about 8 days. Citrus germinated much more slowly, requiring 26 days at 0 bars.
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