Anatomy of Flowering Plants
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SËÇØÑDÅRÝ GRØWTH ÏÑ RØØTS
Epidermis
Cortex
Primary phloem
Cambial ring
Endodermis
Pericycle
Protoxylem
Epidermis
Cortex
Cortex
Vascular cambium
Primary xylem
Secondary xylem
Primary phloem
Cortex
Secondary xylem
Annual ring
Secondary phloem rays
Secondary phloem
Epidermis/Periderm
Different stages of the secondary growth in a typical dicot root
In dicot root, vascular cambium is completely secondary in origin. It
originates from the tissue located just below the phloem bundles (a
portion of pericycle) above the protoxylem forming a complete and
continuous wavy ring. It later becomes circular. Further events are similar
to those of a dicotyledon stem.
Secondary growth also occurs in stems and roots of gymnosperms.
However, secondary growth does not occur in monocotyledons.
The wood is actually a 2° xylem.
Lightest wood is of
Ochroma lagopus.
The most prized
wood of India from
which essential
oil is prepared is
Santalum album.
Most durable
wood is of Tectona
grandis.
Hockey sticks are prepared
from the wood of Morus
alba.
Knot in the wood is formed
by growth of secondary
tissues over wounds of
fallen branches.