and lower epidermis is called the mesophyll (GK meso = in the middle, phyllome = leaf). There are two regions in the mesophyll. They are palisade parenchyma and spongy parenchyma. Palisade parenchyma cells are seen beneath the upper epidermis.
It consists of vertically elongated cylindrical cells in one or more layers. These cells are compactly arranged and are generally without intercellular spaces. Palisade parenchyma cells contain more chloroplasts than the spongy parenchyma cells. The function of palisade parenchyma is photosynthesis.
Spongy parenchyma lies below the palisade parenchyma. Spongy cells are irregularly shaped. These cells are very loosely arranged with numerous airspaces. As compared to palisade cells, The number of stomata is more or less equal on both the epidermis.
The stomata is surrounded by dumb – bell shaped guard cells. The guard cells-contain chloroplasts, whereas the other epidermal cells do not have them. Some special cells surround the guard cells. They are distinct from other epidermal cells.
These cells are called subsidiary cells. Some cells of upper epidermis are large and thin walled. They are called bulliform cells or motor cells. These cells are helpful for the rolling and unrolling of the leaf according to the weather change.
Some of the epidermal cells of the grass are filled with silica. They are called silica cells . Mesophyll The ground tissue that is present between the upper and lower epidermis of the leaf is called mesophyll. Here, the mesophyll is not differentiated into palisade and spongy parenchyma.
All the mesophyll cells are nearly isodiametric and thin walled. These cells are compactly arranged with limited intercellular spaces. They contain numerous chloroplasts. Vascular Bundles Vascular bundles differ in size.
Most of the vascular bundles are smaller in size. Large bundles occur at regular intervals.Two patches of sclerenchyma are present above and below the large vascular bundles. These sclerenchyma patches give mechanical support to the leaf. The small vascular bundles do not have such sclerenchymatous patches.
Vascular bundles are conjoint, collateral and closed . Each vascular bundle is surrounded by a parenchymatous bundle sheath. The cells of the