Xylem fibers, also known as libriform fibers, are thick-walled, lignified cells that provide mechanical support to the plant. While fibers can also occur in phloem (bast fibers), they are a fundamental structural component of the xylem tissue in vascular plants.

In secondary xylem, the axial system (or vertical system) consists of cells derived from fusiform initials, which are oriented vertically. This system includes tracheary elements like vessels and tracheids, as well as xylem fibers and axial parenchyma, all contributing to vertical transport and support.

In an exarch arrangement, the protoxylem develops toward the outside of the organ, meaning it is located at the periphery, while the metaxylem develops toward the center. This pattern is characteristic of the primary roots of vascular plants, distinguishing it from endarch arrangements typically found in stems.

In mesarch xylem, the protoxylem is situated in the center of the bundle and is surrounded by metaxylem on all sides. This arrangement is commonly observed in the vascular bundles of many ferns and some primitive gymnosperms.

In monocot stems, vascular bundles are typically scattered throughout the ground tissue rather than being arranged in a ring. This scattered arrangement is a diagnostic anatomical feature that helps distinguish monocots from dicots, which usually possess a ring-like arrangement of vascular bundles.

In the primary stem anatomy of many herbaceous plants, the region immediately beneath the hypodermis is the cortex. The cortex is primarily composed of thin-walled parenchyma cells, which serve functions such as storage and photosynthesis. While the hypodermis itself may be sclerenchymatous for structural support, the underlying cortical tissue is predominantly parenchymatous in nature.

Xylem parenchyma cells are living cells that remain present in both primary and secondary xylem. They play essential roles in storage, lateral transport of water and nutrients, and sometimes in the formation of tyloses within vessels.

The cuticle is a waxy, hydrophobic layer composed of cutin that covers the epidermis of aerial plant parts. It serves as a critical barrier to prevent excessive water loss through transpiration and provides protection against environmental stressors. It is a standard feature in most land plants, including pteridophytes.

Primary xylem is categorized based on the timing of its development into two distinct forms: protoxylem, which forms first during elongation, and metaxylem, which forms later after the organ has completed its primary growth.

In plant anatomy, the pericycle is a layer of cells located internally to the endodermis and externally to the vascular tissues. It is situated deep within the stem or root structure, well inside the epidermal layer, which forms the outermost boundary of the plant organ.