The foliage leaves are probably the most noticeable organs of a flowering plant. The veins are clearly visible on the leaf blade. The way in which the veins are arranged is known as venation of the leaf . The leaf blades of some plants show indentations or clefts. If the leaf blade is not divided into leaflets , the leaf is termed a simple leaf .
Most monocots have simple leaves, while dicots can have simple or compound leaves.
If a thin transverse section is made through a dorsiventral leaf the different tissues can clearly be observed under a microscope. Three regions are distinguishable, namely the epidermis , the mesophyll and the vascular bundles or veins . The epidermis covers the lower and upper sides of the leaf. Each side is composed of a single layer of closely-packed rectangular cells . The layers are translucent and are covered with a cuticle on the outer wall.