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GRABE, D.F. (ed.) 1970. Tetrazolium Testing Handbook for Agricultural Seeds. Contribution No. 29 
       to the Handbook on Seed Testing,  AOSA. Plate V Crimson Clover.

Photos: Frieda Wertman

Left:
All seeds germinable.  The different degrees of staining reflect different degrees of seedcoat permeability.
The seeds on the right absorbed the tetrazolium solution more slowly and are more lightly stained.

Right:
First seed:  Germinable.  Embryo completely stained.
Second seed:  Non-germinable.  Radicle broken at point of attachment to cotyledons.
Third seed:  Non-germinable.  Unstained areas on cotyledon and radicle.
Fourth seed:  Non-germinable.  Radicle unstained.  Point of attachment of radicle to cotyledons unstained.