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

VIII. BASICS OF PLANT MORPHOLOGY AND ANATOMY

Morphology and Anatomy of the Stem and Shoot

Stem Structure of Dicotyledonous Herbaceous Plants

In herbaceous dicotyledonous plants, the primary stem Structure is formed during early Selection/3.html">Stages of development. It consists of the epidermis, primary cortex, and central cylinder containing primary Vascular Tissues. However, unlike monocots, dicots eventually develop secondary lateral Meristems—the cambium and phellogen—and The activity of these tissues drives the transition to Secondary structure. Two MAIN TYPES OF secondary structure are distinguished in dicots: fascicular (bundle) and non-fascicular (non-bundle). In the fascicular type, the procambium originates within the stem apex as isolated strands, forming discrete vascular bundles arranged in a regular circle. With the appearance of the cambium, open vascular bundles (via fascicular cambium) and medullary rays (via interfascicular cambium) are formed.

The non-fascicular type of stem structure is associated with the activity of a continuous ring of procambium, which immediately begins to function actively, producing secondary phloem toward the outside and secondary xylem toward the center.

In the transitional type of stem structure, the procambium in the apex forms as distinct strands, resulting in a fascicular structure. The vascular bundles are arranged in a circle and separated by areas of parenchymatous tissue known as medullary rays. During the transition to secondary structure, the procambial Cells located between the phloem and xylem of a vascular bundle give rise to the fascicular cambium, while the interfascicular cambium gives rise to the parenchyma of the medullary
ray. The fascicular cambium deposits secondary phloem outward and secondary xylem inward. During the second half of the growing season, the interfascicular cambium begins to produce secondary vascular tissues, forming additional vascular bundles that eventually merge with the primary ones. This process establishes the non-fascicular stem structure characteristic of the common sunflower (Helianthus annuus L.).

The main Anatomical Features of woody plant stems include a non-fascicular structure, the presence of secondary protective tissues—cork and bark—and The ability to undergo annual thickening due to the differentiation of cambial cells into secondary vascular tissues.