Membrane priming - a method for small samples of high value seeds

Membrane priming uses an osmotic solution to control the level of seed hydr ation, employing a membrane, which is permeable to water but not to the osm oticum, to separate the seeds from the solution. A membrane priming unit wa s designed consisting of two concentric cylinders held together by watertig ht end fittings. The inner is perforated with many holes and acts as a supp ort for a cylindrical semi-permeable membrane. The space between the two cy linders is partially filled with a solution of polyethylene glycol 20,000 ( PEG). In use, seeds are placed inside the membrane in the inner cylinder an d the unit is rotated slowly on horizontal rollers. Water at a controlled p otential moves through the membrane and is absorbed by the seeds until thei r water potential equilibrates with that of the solution. The water potenti al of the osmotic solution and the duration of the treatment are optimised for each species. The method appears to be preferable to direct immersion i n PEG solution for mucilaginous seeds or those where oxygen uptake is restr icted by immersion.