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Heartwood differs from sapwood in
A
Being susceptible to pests and pathogens
B
Presence of rays and fibres
C
Absence of vessels and parenchyma
D
Having dead and non-conducting elements
Detailed Solution
In old trees the greater part of the secondary xylem becomes dark brown because of the deposition of organic compounds such as tannins, resins, oils, gums, aromatic substances and essential oils in the central layers of the stem.
This region, called heartwood, consists of dead elements with highly lignified walls; it does not conduct water but gives mechanical support.
The deposits make heartwood hard, durable and resistant to attack by micro-organisms and insects (so it is not more susceptible to pests).
The peripheral, lighter-coloured secondary xylem is the sapwood, which is involved in the conduction of water and minerals.
Rays, fibres, vessels and parenchyma are present in both.
Hence heartwood differs in having dead and non-conducting elements.
This region, called heartwood, consists of dead elements with highly lignified walls; it does not conduct water but gives mechanical support.
The deposits make heartwood hard, durable and resistant to attack by micro-organisms and insects (so it is not more susceptible to pests).
The peripheral, lighter-coloured secondary xylem is the sapwood, which is involved in the conduction of water and minerals.
Rays, fibres, vessels and parenchyma are present in both.
Hence heartwood differs in having dead and non-conducting elements.