Botany - B.Ye. Yakubenko 2017

Part One. Plant Anatomy and Morphology
Chapter II. Histology
2.2. Meristems: Structural Features, Functions, and Classification

Meristematic Tissues, or meristems, are tissues in which Cell Differentiation is not yet complete, and Cells remain capable of continuous division, ultimately giving rise to permanent specialized tissues. The activity of meristematic tissue generates new cells, increases tissue mass and volume, and drives the GROWTH AND DEVELOPMENT of plant organisms. Meristems originate from the embryonic Cells of the seed embryo.

Meristems consist of relatively small, living, tightly packed cells with thin walls and a comparatively large Nucleus. Their shape varies, though they are most commonly parenchymatous or isodiametric.

One of the Characteristic Features of meristematic tissues is their specific localization within the plant body. Accordingly, they are classified into apical (terminal), lateral, intercalary, and wound (traumatic) tissues.

Apical meristems (apices or SHOOT/ROOT apices) are located at the tips of stems and roots, driving the longitudinal growth of these Organs. Lateral shoots and roots develop their own apical meristems. The uppermost layers of the apex are termed promeristems. Within the apex lie initial (stem) cells, whose defining feature is that when they divide to produce a daughter cell, they restore their original shape through growth and retain their capacity for division. Meanwhile, the daughter cells retain The ability to divide for some time, but as they move further away from the initial cell, they differentiate into permanent tissues.

While a single initial cell is typically located at the apex of root tips and stem tips, seed plants generally possess multiple initial cells.

Lateral meristems are situated within the stem or root and are responsible for Secondary Growth in thickness. Lateral meristems include procambium, cambium, pericycle, and cork cambium (phellogen).

Intercalary meristems are located at the nodes of certain plants (such as grasses and horsetails) or at the base of floralscapes, facilitating their rapid elongation.

Based on their origin and function, meristematic tissues are categorized into Primary and secondary. Primary meristems derive directly from the embryonic Tissues of the embryo, whereas secondary meristems develop either from primary meristems or from primary permanent tissues.

Primary meristems include the shoot and root apices, procambium, intercalary meristem, and pericycle; secondary meristems include the cambium, cork cambium (phellogen), as well as fascicular and interfascicular cambium.

Wound or traumatic meristems are secondary in origin and form protective tissue at the sites of organ injury or damage.