This symplast concept is essential to an understanding of compartmentalization. Once the symplast concept is understood, then many parts of the compartmentalization concept fall into place. Just as you cannot have regenerating terms for a generating system, you cannot have dead wood terms for an organ that contains living cells. The iodine stains starch grains purple, and except for a few rare exceptions, the purple dots will only be seen in living cells. The symplast defines the limits of the tree defense system.
Defense is dynamic and protection is static.
As the inner symplast dies, the wood becomes protection wood. Heartwood is genetically age-altered wood that has a greater protection capacity than the sapwood that contains the symplast. False heartwood is wood so depleted of elements essential for life that few organisms can grow in it. False heart- wood is often trunk wood associated with dying and dead branches. As the branches die, the trunk wood associated with the branches deplete their supply of elements, especially nitrogen-based molecules, that are essential for life.