Cattails and wild rice are examples. Other methods are a hot water seed soak, boiling water dip, or room temperature H20 soak for 24 - 48 hours, and various dips in acids. Diameter is approx. Treatment I soak seed in distilled water 48 hours. Soak until cool, one hour.
Microwave ovens emit electromagnetic radiation in the radio wave spectrum.
The microwaves excite H20 molecules, which are bi-polar, causing them to vibrate. This generates heat, increases vapor pressure, and causes the volume of H20 to expand both as a liquid and as a gas. It happens in free water in and around tissues as well as in any intercellular and intracellular water. Seeds were planted in trays, and trays were placed on a warm surface supplying bottom heat. Therefore, all three methods worked equally well to get moisture through the seed coats, and none killed the embryos.