I am often amazed with the way a cut lettuce keeps in the fridge for
so long. As long as you cut off the manky outer leaves, then dunk the
remaining lettuce in cold water for 45 minutes it comes back up
tasting as fresh as when it was bought. Is this because the root
'stub' still provides enough nutrients for the leaves?

I've just prepared one that was bought a week ago and it was fine. It
was probably a few days old already by the time it ended up in
Somerfields. I noticed a similar effect with a fresh cauliflower
recently. I ate half the florets by cutting them off and cooking them,
then I put the remainder still on the root stub back in the fridge. It
was still edible six days later.

MM