While morphology deals with the external form of plants, anatomy is the study of their internal structure and organization. A deep understanding of the internal arrangement of cells and tissues is crucial for comprehending the physiological functions that sustain plant life. Plant tissues are broadly classified into two main groups based on their state of development and capacity for division: meristematic tissues and permanent tissues.

Meristematic Tissues are composed of actively dividing, undifferentiated cells responsible for plant growth. They are typically found in specific regions of the plant. Apical meristems, located at the tips of roots and shoots, are responsible for primary growth, which leads to an increase in the length of the plant. Intercalary meristems, found at the base of leaves or internodes in grasses, also contribute to elongation. Lateral meristems, such as the vascular cambium and cork cambium, are responsible for secondary growth, which results in an increase in the girth or thickness of the plant, primarily in dicots and gymnosperms.

Permanent Tissues are derived from meristematic tissues and consist of cells that have lost the ability to divide and have become specialized to perform specific functions. They are categorized into simple and complex tissues. Simple tissues are composed of a single type of cell. These include parenchyma, thin-walled, living cells that perform functions like photosynthesis, storage, and secretion; collenchyma, which provides flexible mechanical support to young stems and petioles; and sclerenchyma, composed of dead cells with thick, lignified walls that provide rigid mechanical support, occurring as fibers or sclereids.

Complex tissues are made up of more than one type of cell that work together as a unit. The two primary complex tissues are xylem and phloem, which form the vascular system. Xylem is responsible for the conduction of water and minerals from the roots to the rest of the plant and is composed of tracheids, vessels, xylem fibers, and xylem parenchyma. Phloem transports food materials, primarily sucrose, from the leaves to other parts of the plant. It consists of sieve tube elements, companion cells, phloem parenchyma, and phloem fibers.

These tissues are organized into three major tissue systems: the epidermal, the ground, and the vascular tissue system. The Epidermal Tissue System forms the outermost protective covering of the plant body and includes the epidermis, stomata, and epidermal appendages like trichomes and root hairs. The Ground Tissue System constitutes the bulk of the plant body, filling the space between the epidermis and the vascular tissue. It is composed mainly of parenchyma, collenchyma, and sclerenchyma and includes regions like the cortex, pericycle, and pith. The Vascular Tissue System consists of xylem and phloem, which are arranged in distinct bundles. The arrangement of these vascular bundles differs significantly between monocots and dicots.

The internal anatomy of different plant parts reveals key distinctions between dicotyledonous and monocotyledonous plants. In the dicot root, the xylem and phloem are arranged in a radial pattern, and the xylem is typically tetrarch. In contrast, the monocot root usually has a polyarch condition with many xylem bundles. The dicot stem is characterized by vascular bundles arranged in a ring, a well-defined pith, and the presence of cambium, allowing for secondary growth. The monocot stem, however, has vascular bundles scattered throughout the ground tissue, lacks a distinct pith, and does not have cambium, hence it does not undergo secondary growth. The dicot leaf (dorsiventral) has a distinct upper and lower surface, with stomata more numerous on the lower epidermis and a differentiated mesophyll. The monocot leaf (isobilateral) is similar on both surfaces, with stomata distributed almost equally.

Secondary growth is a significant process in most dicotyledonous stems and roots, leading to an increase in their diameter. This is facilitated by the activity of the lateral meristems. The vascular cambium, located between the xylem and phloem, produces secondary xylem towards the inside and secondary phloem towards the outside. The activity of this cambium is influenced by seasonal variations, leading to the formation of distinct annual rings composed of early (spring) wood and late (autumn) wood. Over time, the older, central secondary xylem becomes non-functional and dark-colored, forming heartwood, while the outer, functional region is called sapwood. Another lateral meristem, the cork cambium (phellogen), develops in the cortex and produces cork (phellem) on the outside and secondary cortex (phelloderm) on the inside. Together, these three layers form the periderm, which constitutes the bark of the tree.