BOTANY WITH THE BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VII. PLANT TISSUES

Vascular Tissues

Vascular Bundles

Xylem and phloem are often combined into vascular bundles, which originate from procambium or from both procambium and cambium. Vascular bundles formed solely by procambial meristem are called closed bundles. They consist of primary phloem and xylem (monocots). If a vascular bundle initially forms with the participation of procambium, followed by The Development of cambium that produces secondary phloem and xylem, the bundle is called open. It consists of phloem, cambium, and xylem (gymnosperms and dicots).

Depending on the relative arrangement of phloem and xylem, vascular bundles are classified into radial, collateral, bicollateral, and concentric. Vascular bundles in which xylem and phloem lie on alternating radii are called radial (roots of monocots). In collateral vascular bundles, phloem and xylem are located side by side on the same radius. In bicollateral bundles, the Tissues are arranged in the following sequence: phloem, xylem, phloem (pumpkin). In concentric vascular bundles, either the xylem occupies the central position and is surrounded by a ring of phloem (amphicribral bundle in bracken fern), or the phloem occupies the center and is surrounded by xylem (amphivasal bundle in lily-of-the-valley rhizomes).

A vascular bundle comprising both phloem and xylem is called complete. If a bundle consists of only xylem or phloem, it is referred to as incomplete.

The types of vascular bundles, their arrangement patterns, and The Nature of secondary wall thickening in tracheae and tracheids within roots, stems, leaves, and rhizomes serve as important morphological and anatomical diagnostic features in the microscopic examination of medicinal raw Materials.