First slide

Secondary Growth

Question

Heartwood is durable and resistant to the attacks of microbes and insects due to

Easy

A

secretion of antibiotics.
B

deposition of organic compounds.
C

living nature.
D

presence of highly lignified cells with dense protoplasm.

Solution

In old trees, the greater part of secondary xylem is dark brown due to deposition of organic compounds like tannins, resins, oils, gums, aromatic substances and essential oils in the central or innermost layers of the stem. These substances make it hard, durable and resistant to the attacks of microorganisms and insects. This region comprises dead elements with highly lignified walls and is called heartwood.

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