Describe the internal structure of a maize leaf.

(N/A) $\rightarrow$ The leaf of maize is flat and long. The cells produced in the mid-leaf are of the same type. Structurally,the maize leaf is called an isobilateral leaf.
$\rightarrow$ When a thin section of a maize leaf is stained with safranin and viewed under a microscope,the following layers are observed: $(1)$ Epidermis,$(2)$ Mesophyll tissue,$(3)$ Vascular bundles.
$(1)$ Epidermis: In the leaf,two layers of epidermis are seen.
$\rightarrow$ Upper Epidermis: It forms the uppermost or adaxial layer. It is a single-layered tissue made up of parenchymatous cells. Its outer surface is covered with a protective layer of cuticle.
$\rightarrow$ In the adaxial layer,at certain distances,Bulliform cells are arranged in long rows. These cells are found in groups of $5$ to $7$.
$\rightarrow$ These cells are comparatively larger than other epidermal cells. They lack a thick protective cuticle on their outer wall,making them very thin. Generally,small,unicellular,slanting trichomes are located on both sides of these cells. These trichomes help in moisture absorption; hence,they are called moisture-absorbing trichomes.
$\rightarrow$ The presence of bulliform cells distinguishes the adaxial layer from the abaxial layer. In a humid atmosphere,bulliform cells absorb water,become turgid,and expose the leaf surface. In a dry atmosphere,due to water stress,they become flaccid,causing the leaves to curl inwards to minimize water loss. Thus,these cells are also called motor cells. Because they are round and bubble-like,they are termed bulliform cells.
$(2)$ Mesophyll Tissue: Since the leaf possesses an isobilateral structure,there is no differentiation into palisade and spongy parenchyma.
$\rightarrow$ All cells are alike and contain an equal amount of chloroplasts.
$\rightarrow$ Only palisade-like tissue is located between both epidermis layers in the maize leaf. These cells are round or oval with intercellular spaces. Air-filled sacs are seen clearly below the stomata,which are called respiratory cavities.
$(3)$ Vascular Bundles: Maize is a monocot plant with parallel venation; therefore,vascular bundles are cut vertically in a cross-section. They are located at equal distances from each other.
$\rightarrow$ Vascular bundles are conjoint,collateral,and closed.
$\rightarrow$ Vascular bundles are of both large and small types. The xylem is located towards the adaxial layer,and the phloem tissue is located towards the abaxial layer.
$\rightarrow$ Each vascular bundle is surrounded by a sclerenchymatous bundle sheath. This sheath extends to both the adaxial and abaxial layers,providing structural strength to the leaves.