Effect of polyethylene glycol exclusion on the water potential of solution-saturated filter paper

Solutions of high molecular weight polyethylene glycol are often used to control water potential in seed germination studies. There is an implicit assumption that the seed support materials do not alter the water potential of the osmotic solution. Filter paper, however, contains a hydrophylic volume fraction that is inaccessible to high molecular weight polymers. Water absorbed by filter paper filters was found to concentrate polyethylene glycol and lower water potential in solution-filter paper mixtures. The magnitude of this concentration effect is a function of the original concentration of polyethylene glycol and the ratio of solution volume to filter paper weight.