Rot, Decay
A tree is stuck in a prison under the ground and it's starting to rot and decay.
Trees can't live without sunlight, and it's too damp underground in a prison. The water gets all moldy and the tree will rot and die.
きゅう
く
None
You get close to the rotting tree and see some rotten cucumbers (きゅう) hanging from its branches. No!
This poor cucumber tree, left in this ground prison to rot. There's nothing worse than eating a rotten cucumber.