MONOCOTYLEDONOUS
STEM
The monocot stem possesses only primary structure. The
different monocot stems from outside towards inside are
consist of epidermis, hypodermis, ground tissue and
vascular system.
1. Epidermis
It is single-layered, having stomata in it. The cells have a
thick cuticle layer on the outside.
2. Hypodermis
It is 2-3 layered having lignified sclerenchymatous cells
present just below the epidermis.
3. Ground Tissue
It fills the whole interior of the stem containing
parenchymatous cells. A number of vascular bundles are
scattered in it.
4. Vascular System
Monocot stems has scattered vascular bundles.
Each vascular bundle in vascular strand is surrounded by
sheath of sclerenchyma known as bundle sheath cells. The
vascular bundles possess both phloem (phloem parenchyma is
absent) and xylem so, these are conjoint type.
The bundles are endarch with the protoxylem and metaxylem
are arranged in the form of a ‘Y’. The divergent ends are
occupied by two pitted vessels and convergent end by two
smaller spiral vessels lying radially in the centre. A water
containing cavity called lysigenous cavity is present in
association with the protoxylem.
It is formed by the breakdown of inner protoxylem vessels
and parenchyma during the earlier stages of growth. The
cavity is absent or reduced in the smaller vascular bundles that
occur in contact with sclerenchymatous hypodermis.
Features for Identification of
Monocotyledonous Stem
Monocotyledonous stem can be easily identified with the
following features
(i) Sclerenchymatous hypodermis is present.
(ii) Undifferentiated ground tissue.
(iii) Vascular bundles scattered throughout ground tissue.
(iv) Vascular bundles are conjoint, collateral and closed.
(v)’ Protoxylem cavity is present.