OAK          Heartwood forming tree

#1 You can see the white sapwood.  Take note that the width of the sapwood in the longitudinal plane is consistent with the inner heartwood.

#2 and #3 You can see the color altered wood (formally known as discolored wood) within the heartwood,  which is from a wound or injury.  You can have color altered wood in heartwood.  The color altered wood will decay first.  The color altered wood is a protection wood just as the heartwood is a protection wood.  Heartwood color is from an aging process.  The color altered wood is from a wound or injury.

#3 Has decayed.  You can see the decay does not extend into the sapwood or symplast.  Microorganisms do not move freely in trees.  They respect boundaries often.

Image source (SHIGO, 2002)

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