Vaatbundels

Vaatbundels, or vascular bundles, are the threadlike strands of vascular tissue in higher plants that transport water, minerals, and organic nutrients. Each bundle typically contains conducting xylem and phloem, and is often surrounded by supportive and storage cells. In stems and leaves, vaatbundels form continuous networks that link roots with photosynthetic tissues, enabling long-distance transport and mechanical support.

In stems, vascular bundles are discrete strands. In dicotyledonous plants they tend to form a ring around the pith, contributing to secondary growth through a vascular cambium. In monocotyledon plants they are usually scattered throughout the stem and lack a vascular cambium, limiting broad secondary growth.

In leaves, veins are composed of vascular bundles organized in a midrib and network. Each bundle contains xylem toward the upper side and phloem toward the lower side in a collateral arrangement, though other patterns occur in some species. In some stems, bundles are collateral; in others they are bicollateral or concentric, reflecting variation among taxa.

Development and function: Xylem conducts water and minerals from roots to shoots; phloem distributes sugars from photosynthetic tissues to non-photosynthetic parts. The vascular cambium, when present, enables secondary growth and thickening. In roots, the vascular tissue forms a central stele with xylem and phloem arranged in characteristic patterns.

Significance: The arrangement and composition of vaatbundels influence transportation efficiency, mechanical strength, and growth patterns across vascular plants, and show diversification across plant lineages.