fosheezy

wow what a thread. the way i understand wall 4 is (*suck in a deep breath*);
-the cambium grows putting xylem cells on the inside and phloem on the outside as per usual. trunk is expanding. tree is happy.
-tree is wounded.
-instead of putting another layer of unprotected xylem on the inside a heavily suberised layer of cells are laid down (suberin is the same waterproof and inpenatrable substance in bark that stops infection from the outside).
-bam, barrier zone is laid down and cambium goes back to producing xylem.
-if walls 1,2, and 3 are all breached; so be it, all the new wood is protected by an 'inner bark'.
-tree is happy again (although has lost significant storage capacity)

-and woundwood grows to close the wound re-instating the surface area for which the cambium can pruduce tissue, but does not compartmentalize decay (all walls have already been laid down). and yes, when the wound is closed there will be very little oxygen for decay, but that does not mean zero oxygen! if oxygen could not get through wood there would be no living cells within it when we all know rays are living cells.

whateva', peace out hombre's.
anton.