Nice graphic, the cambium is a good indicator as to whether a tree is alive/has a dead branch. Xylem is what transports water. If that is damaged you can have some longer term issues depending on the severity.

I had an Alaskan cedar that had 50% heartwood exposed on one side. It was alive but I didn't want to invest in the tree at that point.

Xylem is not an outside layer. It's the inner most part of the tree, and makes up the sapwood and heartwood. New sapwood is "living" (definitions of this vary) and transports water and nutrients up from the roots to the leaves. As the sapwood ages, it gradually dies (or at least becomes far less active), and is referred to as heartwood. There is a continuum between the sapwood and heartwood: it's not two distinct layers.

Cambium does not transport water, sap, or RoundUp.

Phloem, the tissue that carries sap through the tree in either direction, is what is responsible for transporting RoundUp.

toronado,
See link below. It spells out what each layer is and what it becomes.

Arktrees

Here is a link that might be useful: Anatomy of a tree trunk and funciton