Internal structure of leaf

1. Manoj Das

2. Leaves
• Leaves are green lateral appendages of shoot system that
help in gaseous exchange as well as photosynthesis. Leaves
are of two types-
• Dorsiventral leaf
• Isobilateral leaf

3. Differences between dorsiventral and isobilateral Leaves
Dorsiventral leaf
• It occurs in Dicots
• The sunlight can expose on
dorsal surface.
• It shows reticulate venation
• Stomata are distributed in the
ventral surface.
• Stomata are reinform or kidney
in shape.
Isobilateral leaf
• It occurs in monocot
• the sunlight can expose on both
surfaces.
• It shows parallel venation.
• Stomata are found in both
surfaces.
• Stomata are dumbbell in shape

4. The
• The mesophyll is differentiated into
palisade and spongy parenchyma.
The bundle sheath is
parenchymatous or
collenchymatous.
The bulliform cells are absent
• The mesophyll is not differentiated.
• The bundle sheath is
sclerenchymatous.
• The bulliform cells are present.

5. Internal structure of dorsiventral leaf
T.S of Mangifera indica leaf shows following structure-
1. Epidermis- The leaf shows distinct upper and lower epidermis.
The upper epidermis is made of single layered compactly arranged
Parenchymatous cells. These lack chloroplasts and stomata are
absent.
The lower epidermis is also a single layer of cutinized cells. The
stomata are present.

6. • 2. Mesophyll-This tissue occurs between the two epidermal
layers. It is differentiated into palisade and spongy parenchyma
• The palisade parenchyma is located just below the upper
epidermis. Cell are radially elongated with numerous
chloroplasts close to the wall. About 2-3 layers of palisade
parenchyma are generally present.
• The spongy parenchyma forms rest of the mesophyll. It is
situated near the lower epidemies, Cells are small and of
various shapes and size. Numerous chloroplasts are present in
these cell. Large intercellular spaces occur in between spongy
parenchymatous cells. These are also known as air chambers.
Some of these air chambers open into sub-stomatal chambers.

7. • Vascular bundles- The size of the VBs continues to decrease
progressively from base towards the apex of the leaf. Each
VB consists of xylem placed towards the upper epidermis
and phloem situated towards the lower epidermis. Each VB
is conjoint, collateral and closed. The VB is surrounded by a
parenchymatous bundle sheath. Parenchyma often
collenchyma cells occur on both upper and lower sides of
the VB and reach up to the epidermis, This tissue is known as
bundle sheath extension.
The xylem consists of tracheary elements and phloem
of sieve tubes and companion cells. Protoxylem is directed
towards the upper epidermis and the metaxylem towards the
lower epidermis.

9. Internal Structure of Isobilateral leaf
V.S of maize leaf shows following regions-
• 1. Epidermis- The leaf is coated by thick cutinized epidermis on
both sides. Stomata are found in lower and upper epidermis.
Some of the cells of the epidermis are swells to form motor or
bulliform cells.
• 2. Mesophyll- This tissue is located between the two epidermal
layers. It is composed of spongy parenchyma of varied shapes
and sizes, leaving large number of intercellular spaces. The
cells posses abundant chloroplasts.

10. • 3. Vascular bundles- These are arranged in a parallel series. VBs
differ in size. Each VB is conjoint, collateral and closed type. A
parenchymatous bundle sheath surrounds the bundle. A patch
of sclerenchyma occurs on the both the ends of each VB which
extends up to the epidermis on their respective sides as bundle
sheath extension. The xylem is located towards the upper side
while the phloem is present on lower side