The Leaf

Lab -7- The Leaf
A leaf is an aerial and lateral outgrowth of the stem of a usually flat and dorsiventral anatomy. It functions mainly to manufacture food by photosynthesis and consists typically of a stalk also called petiole, a flattened blade, the lamina, and the leaf base. Strands of conducting and strengthening tissues, the veins, run through it. Their pattern, also called leaf venation, is a feature of characterization. Leaves may be simple, i.e. undivided or compound (composed of several parts called leaflets). The blade margin and the leaf arrangement at the stem are further features of characterization.

Simple Leaves :- Simple leaves have one leaf blade. The leaf may be irregularly shaped, but it is still one blade with one leaf stalk.

Compound Leaf :- Compound leaves are made of many individual leaflets that are all attached to the same leaf stalk

Modified Leaves :- Some leaves have many unusual shapes and sizes. This allows them to adapt to protect the plant, to store food, or to adapt to the environment in which they grow.

Leaf Arrangement
Alternate:- In an alternate arrangement, single leaves are attached spirally along the stem.
Opposite:- Two leaves emerge opposite each other on a stem.
Whorled:- In a whorled arrangement, several leaves emerge together around a stem node.

Leaf Tissues
The leaf blade’s outer surface is epidermal tissue and the ground tissue within is photosynthetic mesophyll, interspersed with “veins” (vascular bundles) of conducting (vascular) tissue. Vascular connections between blade and stem pass through the petiole.

Dicot Leaf
Epidermis:- There may be one or more layers of epidermal cells with cutinized outer walls that form a waterproof outer surface. Stomata of guard cells are present on the upper and lower surface or only on the lower surface. Various hairs and glands may also be present .

Ground Tissue:- The parenchyma cells of the ground tissue are divided into palisade and spongy mesophyll. Usually the columnar cells of the palisade layer lie under the upper leaf epidermis and contain most of the chloroplasts of the ground tissue. The spongy parenchyma has irregular-shaped cells with air spaces between and lies above the lower leaf epidermis.

Vascular Tissue:- Four small vein transections are shown which are part of the vast, interconnecting network between major veins. A leaf vein (vascular bundle) usually has xylem on the upper side and phloem on the lower side. The reverse may be true in major veins. A layer of parenchyma cells called a bundle sheath , which functions in