Leaves

Internal structure of leaf

1. Manoj Das Internal structure of leaves

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- 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.

8. 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.

9. 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