From the pictures I have put up it's fairly explicit what I see.
I see no wall 4 where there is no wood.
If we're going to debunk wall 4 being callus then I need blatant evidence that a blind man can see.
Source:
Decay development - Maintenance - Landscape plants - Edward F. Gilman - UF/IFAS Quote:
Wall 4: This is the strongest boundary that retards spread of discoloration and decay in trees. This reaction zone forms from the cambium along the edge of the outer-most growth ring present at the time the tree was injured. It begins at the point where the tree was injured and it may extend all or part way around the tree. Wall 4 stays in the same position in the tree but may extend further around or up and down the trunk with time. It does not move out with the new cambium. There may be numerous wall 4s in a tree, depending on its wounding history. Wall 4 forms the edge of a hollow.
Wall 4 develops in response to many different types of injuries. It can take several years for wall 4 to reach the other side of the trunk - or it may never reach that far. Wall 4 extends above and below the injury essentially in the shape of a pipe. It may develop a few inches or many feet above and below the injury.
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Source:
Tree Anatomy Quote:
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Wall 4 is formed by cambium growth after an injury. It is the strongest of all the walls. Internally, it separates the wood present at the time of injury from new wood formed as the tree grows. Externally, callus tissue develops around the injury and should eventually cover it by growing over the dead wood.
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Diagram:
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Now this find, IMHO, is the greatest piece on it I've read. It goes into extreme detail microscopically with pictures and all. I have attached a PDF of it also but the online pics are clearer/larger and more colourful.
Quote:
Originally Posted by arborcraft  No Ekka, I think that's wrong.
You can have one without the other. The callus growth doesn't carry the barrier zone. You can have Wall 4, the barrier zone, without the callus.
If over the years the callus growth is very slow, then the lack of callus might mean the tree eventually loses the race, but the lack of callus doesn't mean that Wall 4 wasn't set up.
The extra strength of callus is interesting, but irrelevant in this discussion. |
It appears to me that callus is what it's all about.
Developmental Stages and Fine Structure of Surface Callus Formed after Debarking of Living Lime Trees (Tilia sp.) -- STOBBE et al. 89 (6): 773 -- Annals of Botany