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Anatomy of Dicot and Monocot Leaves
The cross section of the lamina of the leaf exhibits epidermis, mesophyll and vascular system. The epidermis covers both upper surface and the lower surface of the leaf and bears cuticles. The lower surface of the leaf bears stomata. The tissue between upper and lower epidermis is called as mesophyll. In the mesophyll, chloroplasts are present which are responsible for performing photosynthesis. The mesophyll is composed of the palisade parenchyma and spongy parenchyma. As the name suggests, the palisade parenchyma is elongated cells arranged vertically and the spongy parenchyma is rounded cells arranged loosely, situated below palisade parenchymatous cells. Numerous large spaces and air cavities are present between the parenchymatous cells.
The vascular system is composed of vascular bundles present in the veins and the midrib. The size of vascular bundles depends on the size of veins. The vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.
Figure 1 Transverse section of dicot leaf:
The monocot leaf is similar to dicot leaf in many ways, however, in monocot leaf, the stomata are present on both upper and lower surface of the epidermis. The mesophyll layer is not differentiated into palisade and spongy parenchyma. One of the characteristic features of monocot leaf is that certain cells of the upper layer of epidermis present in the veins are modified into large empty colorless cells known as bulliform cells. In the presence of water, the bulliform cells in the leaf absorb water and become turgid, thus exposing the leaf surface. However, in the absence of water, the bulliform cells lose water thus resulting in curling of leaves inwards to minimize loss of water.
Figure 2 Transverse section of monocot leaf
The increase in girth of the dicotyledonous plants is defined as secondary growth. Two lateral meristems involved in secondary growth are vascular cambium and cork cambium.