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Cotyledons Abnormal - 1/2 or more of the original cotyledon tissue damaged.
One type of necrosis on lettuce cotyledons is a physiological breakdown of the plant tissue, the cause of which has not been determined.  It first appears on or adjacent to the midrib and lateral veins.   The symptoms of physiological necrosis often occurs in aged seed.

cotyledons more than 1/2 decay (abnormal)	cotyledons with more than 1/2 total area physiological necrosis (abnormal)
physiological necrosis more than 1/2 area (abnormal)	physiological necrosis more than 1/2 area (abnormal)