If any of these stages are blocked, the seed remains in a state of dormancy. If the seed does not imbibe moisture, scarification is necessary. Scarification involves physical or chemical treatments to open the seed coat to allow entry of water. Every seed batch should be evaluated for purity and percentage of sound seed prior to storage, periodically during storage, and again just before sowing. For seed evaluation, a limited but representative sample should be taken from the entire seed lot.
Purity is determined by inspection and separation of the sample.
Pure or clean seeds are put aside and weighed separately. Purity can be expressed as the weight of clean seeds of a species divided by the weight of the total sample including impurities. The percentage of sound seed can be determined by different methods, depending on the species. A cutting test requires experience with the species being tested. Seeds are cut open and those with firm, undamaged, fully developed and healthy looking tissue are considered viable.