Heartwood  - Heartwood is genetically age-altered wood that has a greater protection capacity than the sapwood that contains the symplast.  In more detail - Heartwood is age-altered wood.  The wood is altered to a higher state of protection than the sapwood.  Sapwood maintains an active defense system because of living cells.  Defense is a dynamic process.  Protection wood has many features that resist infection by decay-causing microorganisms.  As cells age and die in some species, the cell walls and lumens are impregnated with substances that impart a protective feature to the wood.  These substances are called extractives because they can be extracted from the wood by using various solvents.  The heartwood is also more protective because it no longer has stored energy reserves, and the moisture content is low.  Also, as the parenchyma cells die, nitrogen-based materials move out to the sapwood.  Because of the low moisture content, lack of energy reserves and nitrogen-based substances, and the inclusion of extractives, the heartwood usually has a high resistance to microorganisms that cause decay.  SOME MYTHS ON HEARTWOOD from (100 TREE MYTHS SHIGO, 1993).  Myth 42.  CENTERS OF TREES ARE THE WEAKEST PARTS AND ALWAYS ROT FIRST - A MYTH.  Centers of trees are often sound while rot develops in other places.  The most economically damaging rot in the world is caused by Fomes pini and its closely related forms (see Chapter 26 in A NEW TREE BIOLOGY, SHIGO, 1986 page 379).  The rots are typical ring rots that form bands of rot within the heartwood.  The heartrot concept implies that heartwood-rotting fungi grow at will in dead heartwood.  And, further, because the center heartwood is the oldest, and weakest, that is the reason why there are so many hollows in trees.  The ring rots alone make the heartrot concept very difficult to understand because the rots develop with sound heartwood on both sides of the columns.  Ring rots follow the pattern of protection wood formed by the tree as given in Chapter 26 in SHIGO, 1986

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