More attention was focused on the protection boundary that formed after wounding, as shown by arrows in this western hemlock wounded by a black bear. The boundary was called a barrier zone. The barrier zone was characterized as a tissue that had a great amount of axial parenchyma, few conducting elements, low amounts of lignin, and in some species, suberin in the cells. Chemical boundaries within the wood present at the time of wounding resisted spread of the pathogens within the wood present at the time of wounding. This chemical boundary is called the reaction zone.
[A note from the web master. I believe this is now what we call the barrier zone an not a reaction zone. (Where the arrows are pointing.) The zones set within the area of the barrier zone we now call them reaction zones. JAK2004] Reference Page 8 Tree Basics - Shigo.
Page 42 from A New Tree Biology - Shigo