Biology Today — December 2017

Economic

importance

of cork

Prevention of loss of

water by evaporation.

Light, compressible, non

reactive and fire resistant.

Protection against entry of microorganisms,

mechanical injury and extremes of temperature.

Light, being filled with air, hence used as

bottle stoppers, shock absorber, insulator.

Significance of Secondary Growth

Adds girth to plant and provides

support to its increasing weight.

The corky bark produced, protects the interior

from abrasion, heat, cold and infection.

Adds new conducting tissues for replacing old

nonfunctioning ones for meeting increased demand.

An Overview of Secondary Growth in Dicot stem

Primary and secondary growth in a three-year-old stem

Epidermis

Primary phloem

Periderm (mainly cork

cambia and cork)

Secondary phloem

Secondary xylem

Vascular cambium

Primary xylem

Pith

2.

3.

1.

Cortex

Epidermis

Primary

phloem

Vascular

cambium

Primary xylem

Pith

Cortex

Remnant of cortex Remnant of epidermis

Secondary phloem

(inner bark)

Periderm (outer bark)

Remnant of

primary xylem Remnant of pith

Vascular cambium

Secondary xylem

(wood)

Remnant of

primary phloem

Remnant of pith Vascular cambium

Remnant of

primary xylem

Secondary phloem

(inner bark)

Periderm (Outer bark; remnants of

primary phloem, cortex and epidermis

are gradually crushed or torn apart

Secondary and sloughed off)

xylem (wood)