Quote:
Originally Posted by Ekka  Excellent Bob.
As I understand it in prefered environments trees have more energy to store and that improves the defense qualities of the heartwood.
Here's another curly question, rays, can they also transport into heartwood to supply resistance to pathogens? |
I posted the following yesterday, but it seems to have gotten lost in the Pacific somewhere on the way across.
This information came from a site at Purdue University. I will enclose the link to the page at the bottom. There are two parts to it, one addressing rays and other parenchyma cells in the heartwood and the part the play in rot resistance, the second deals with some information on parenchyma cells in general. Hope it helps.
"Often, the wood in is a lighter color toward the outside and darker in the center. These two areas of xylem are the sapwood and heartwood. The sapwood is the physiologically active portion of the xylem, where tracheids and vessels are used for conduction of water and dissolved nutrients, and the parenchyma cells are alive and function in carbohydrate storage. The heart-wood is nonfunctional and even the parenchyma cells are dead. They may have died because they were buried by accumulating layers of oxygen-limiting xylem. It is more likely that they died because the tree used these cells as a dump site for its own toxic waste - tannins and phenols. The heartwood is particularly decay-resistant because of the accumulation of these compounds, which account for its darker color too."
"The fourth type of xylem cell is the parenchyma, an undifferentiated cell that remains alive in the xylem for several years. These cells are scattered in the xylem and constitute the vascular rays, which provide a pathway for lateral movement across the xylem. Like the other parenchyma cells in the xylem, they the storage sites for carbohydrates essential for the vitality and growth of trees. These living parenchyma cells allow the tree to respond to wounds. The callus that forms around the edges of a wound on the trunk or a pruned branch arises from the totipotent parenchyma cells in the xylem. Parenchyma cells at the bottom of a stem cutting begin to divide and form roots whereas those at the upper end of the cut-ting develop into shoots."
http://www.fnr.purdue.edu/inwood/pas...ees%20grow.htm