Biology Today — December 2017

CASE STUDY OF SECONDARY GROWTH IN ROOT AND STEM

Secondary Growth in Ficus Root

Lenticel

Cork

Cork cambium

Secondary cortex

Secondary phloem

Secondary xylem

Cambium

Primary phloem

Primary xylem

Pith

Fibre

Fig.: T.S. of root of Ficus (diagrammatic)

Cork cambium

Secondary phloem

Secondary xylem

Conjunctive tissue

Medullary ray

Tannin

Cambium

Primary phloem

Pith

Metaxylem

Protoxylem

Fibre

Lenticel

Cork

Contains many layers of thick suberised cells

showing characteristic brick like arrangement

Secondary cortex

Comprises of few layers of parenchymatous cells.

Some cells of this region contain chloroplasts

while a few others show thick walled fibres.

Tannin filled cells are also abundant.

Conjunctive tissue

Fig.: Ficus : Detailed structure of a part of T.S. of root

Thin and thick walled prosenchyma that

generally constitutes conjunctive tissue.

Note: Presence of chloroplast in cortex indicates aerial

nature of root. Abundant secondary xylem and phloem

Primary xylem indicate mechanical function of root.

Secondary Growth in Vitis Stem

Vitis vinifera (grapevine) is a liana type of plant and is appropriate for the study of internal structure of a

typical dicot stem. The transverse section of its stem showing the various parts of both primary and secondary origin is

as follows.