What are sapwood and heartwood?
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The wood of the older stems (Under species Dalbergia, Acacia) gets differentiated into two zones, the outer light coloured and functional sapwood or alburnum and the inner darker and nonfunctional heartwood or duramen.
The tracheids and vessels of the heartwood get plugged by the ingrowth of the adjacent parenchyma cells into their cavities through the pits. These ingrowths go by their names as tyloses (which are bag like small micro structures inside the vessel).
Ultimately, the parenchyma cells become lignified and dead. Various types of plant products are available like oils, resins, gums, aromatic substances, essential oils and tannins are deposited in the cells of the heartwood. These substances are collectively called extractives. They provide a deep tinge colour to the heartwood. They are also antiseptic in nature.
The heartwood is, therfore, stronger and more durable (hence called duramen) than the sapwood.
One more special cause is that it is resistant to the attacks of insects and microbes. However Heartwood is liable to be attacked by wood rooting fungi. As a result Hollow wood trunks (which are seen in many places) are due to their activity.
The tracheids and vessels of the heartwood get plugged by the ingrowth of the adjacent parenchyma cells into their cavities through the pits. These ingrowths go by their names as tyloses (which are bag like small micro structures inside the vessel).
Ultimately, the parenchyma cells become lignified and dead. Various types of plant products are available like oils, resins, gums, aromatic substances, essential oils and tannins are deposited in the cells of the heartwood. These substances are collectively called extractives. They provide a deep tinge colour to the heartwood. They are also antiseptic in nature.
The heartwood is, therfore, stronger and more durable (hence called duramen) than the sapwood.
One more special cause is that it is resistant to the attacks of insects and microbes. However Heartwood is liable to be attacked by wood rooting fungi. As a result Hollow wood trunks (which are seen in many places) are due to their activity.
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