MONOCOTYLEDONOUS
(ISOBILATERAL) LEAF
Monocot leaves are generally isobilateral (Isos — equal; bis —
twice; latris— side), but in some plants (Musa, Canna, etc.),
these are dorsiventral. The leaves usually show parallel
venation (veins running parallel to each other).
The various components of a monocot leaf are
1. Epidermis
The leaf composes of upper and lower epidermis made up
of single-layered, compactly arranged cells. The upper layer
is covered with cuticle. In some grasses, the epidermal cells
are impregnated with silica. The stomata are generally
found in both the upper and lower layers of epidermis.
At some places, the epidermis possesses large sized,
thin-walled, colourless protruding cells called bulliform or
motor cells. These become placcid when water ‘is not
sufficient. The leaves again become flat when water is
available and bulliform cells become turgid. The bulliform
cells may be distributed irregularly or arranged in regular
pattern.
2. Mesophyll
It is made up of chlorenchymatous ground tissue of leaves.
It is undifferentiated (i.e., not differentiated between
palisade and spongy parenchyma) in monocot leaves.
All the cells are similar. The intercellular spaces are connected
the two with substomatal cavities. Mesophyll cells contain
abundant chloroplasts. Hence, they are the seat of
photosynthesis.
3. Vascular Bundle
A large number of vascular bundles is present, some of them
are small and some are big. Each vascular bundle is
surrounded by a bundle sheath of parenchymatous cells.
Above and below the larger bundle, the patches of
sclerenchymatous cells are present.
The vascular bundles are conjoint, collateral, endarch
and closed. In some grasses, these are surrounded by a
distinct parenchymatous bundle sheath. The xylem is
present towards the upper epidermis and phloem
towards the lower epidermis.
The xylem and phloem elements of monocot leaves are
similar to those of dicot leaves.
4. Midrib
It is the widest part of monocot leaf. A shallow groove
is present in the upper or adaxial surface, while a broad
ridge is present on the abaxial surface.
Features for Identification of
Monocotyledonous Leaf
Monocotyledonous leaf can be easily identified with
the following features
(i) Undifferentiated mesophyll.
(ii) Presence of bundle sheath with chloroplasts.
(iii) Vascular bundle with xylem towards upper side
and phloem towards lower side.
(iv) Xylem vessels are rounded.
(v) Presence of few large sized bulliform cells on
upper surface.