Page 20 - LN-ANATOMY OF FLOWERING PLANT

Mesophyll is absent in the region of midrib and other larger veins. Collenchyma or
sclerenchyma occur towards the two epidermal layers for providing mechanical
strength. The centre contains a number of vascular bundles, which are embedded in
a parenchymatous ground tissue.
Features for Identification of Dicotyledonous Leaf
Dicotyledonous leaf can be easily identified with the following features
(i) Bifacial flattered with stomata mostly on upper surface.
(ii) Mesophyll differentiated into palisade and spongy parenchyma. .
(iii) Vascular bundles with colourless bundle sheath (in C4-plants).
(iv) Vascular bundle with xylem towards upper side and phloem towards lower side.
The vascular bundles can be seen in the veins and the midrib. The size of vascular
bundles vary according to the size of the veins.
The veins vary in thickness in the reticulate venation.
Mesophyll is absent in the region of midrib and other larger veins. Collenchyma or
sclerenchyma occur towards the two epidermal layers for providing mechanical
strength. The centre contains a number of vascular bundles, which are embedded in
a parenchymatous ground tissue.
Features for Identification of Dicotyledonous Leaf
Dicotyledonous leaf can be easily identified with the following features
(i) Bifacial flattered with stomata mostly on upper surface.
(ii) Mesophyll differentiated into palisade and spongy parenchyma. .
(iii) Vascular bundles with colourless bundle sheath (in C4-plants).
(iv) Vascular bundle with xylem towards upper side and phloem towards lower side.
3.Vascular Bundle
A large number of vascular bundles are 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) Presence of large sized bulliform cells on upper surface.
(ii) Undifferentiated mesophyll.
(iii) Presence of bundle sheath with chloroplasts.
(iv) Vascular bundle with xylem towards upper side and phloem towards lower side.
(v) Xylem vessels rounded.
Secondary Growth
The growth of the roots and stems in length with the help of apical meristem is
called the primary growth. Apart from primary growth, most dicot plants exhibit the
increase in girth. This increase is called secondary growth.
Secondary Growth in Dicot Stem
In a dicot plant, secondary growth in stem occurs both in the stele and in the cortex.