Viability: Whether a Seed Is Alive, Regardless of Whether It Can Germinate Now
A seed lot germinates badly, and the question is whether it is dead or merely resting. A germination test will not answer that, because a dead seed and a dormant one look identical there: unchanged. Viability is the seed’s capacity to live, meaning the ability of its tissue to germinate once conditions allow it. Rather than being waited out, it is made visible on the cut grain.
How it is measured
The method rests on a colour reaction. Living cells carry dehydrogenases, enzymes of cell metabolism, and these turn a colourless test solution red. Whatever turns red was alive when the seed was cut open.
The procedure for hemp is documented: two replicates of one hundred seeds each soak in water for twenty-four hours so the tissue softens and the enzymes activate, are cut lengthwise, and are then stained for sixteen hours at 30 °C in a one per cent solution. Assessment happens under sevenfold magnification.
A second laboratory works on the same question with three replicates, eighteen hours in water at 20 °C, the fruit wall removed instead of a lengthwise cut, and eighteen hours of staining. The steps vary between laboratories; the principle does not.
What counts as viable
A seed counts as viable when its embryo, axis and cotyledons alike, stains an even red throughout. If it stays unstained, comes out blotchy, or leaves more than half of the cotyledons pale, it counts as non-viable.
That distinction has a side effect which lowers the figure without any ageing having occurred: an empty seed with no embryo stains nothing and lands in the same group. Across five lots examined, empty seeds made up 15 % and 14 % in two of them, against only 3 % to 6 % in the other three. The authors name poor seed processing as the most likely cause without having tested it.
What the figure is good for, and what it is not
Its advantages are speed and independence from the seed’s current state: staining is finished within forty-eight hours where a germination test needs seven days, and dormancy does not distort it. Anyone asking whether an intervention on a weak lot can recover anything at all gets the answer before starting.
Its drawback is that actual development plays no part in it. An embryo that stained red can still push out a crooked root. The authors of the hemp study therefore treat the germination test as the more accurate measure of living seed, because root and shoot are genuinely assessed there rather than a colour reaction.