PLANT ANATOMY - Y.I. Korniyevsky - 2017

Lecture Notes

Lecture No. 2. PLANT TISSUES

Lecture Outline

1. Meristematic Tissues

2. Dermal Tissues

3. Secretory Tissues

4. Mechanical tissues

5. Vascular Tissues

6. Ground tissues

Tissues are aggregates of Cells that share a common origin, similar Morphology, and perform the same function (or, a tissue is a stable, regularly recurring complex of cells similar in origin and Structure, adapted to perform one or more Functions). In some tissues, intercellular substances devoid of cellular structure are found between the cells.

Depending on their function, tissues are classified into several types: meristematic, ground, vascular, dermal, and mechanical; many of these can be further subdivided into more specific groups. Dermal, vascular, mechanical, and ground tissues (permanent plant tissues) originate from meristematic tissue, whose cells continuously divide and give rise to permanent tissues.

A true tissue is defined as a group of cells sharing a common origin, similar structure, and function.

1. Meristematic Tissues

Meristematic tissue (meristem) gives rise to all permanent tissues and drives organ growth. Meristematic cells are parenchymatous, living, thin-walled, tightly packed, with dense Cytoplasm, a large Nucleus, and an Abundance of Ribosomes; Plastids are present as proplastids and leukoplasts, while vacuoles are either absent or very small. Meristematic cells that remain in a state of continuous division are called initials, whereas those derived from them that undergo differentiation are termed derivative cells (or derivatives of initials), or fundamental meristem.

Meristems are classified according to their origin (Primary and secondary) and their Location within the plant body.

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2. Dermal Tissues

The functions of dermal tissues include protecting Organs from evaporation, desiccation, cooling, and mechanical damage, as well as facilitating gas exchange (guard cells) and Water absorption (ROOT hairs). Depending on their origin and histological composition, dermal tissues are categorized into primary (epidermis), secondary (periderm), and tertiary (bark, including ring and scaly bark) tissues. Tissues performing both protective and absorptive functions include the epiblema and velamen, while the exodermis and hypodermis serve protective and water-storage functions.

Anomocytic (Greek anomos - irregular) - cells surrounding the guard cells do not differ from ordinary epidermal cells (found in all groups except conifers)		Diacytic (Greek dia - separate, through) - two subsidiary cells are present, with their common wall perpendicular to the stomatal pore (mint, thyme, soapwort)
Anisocytic (Greek anisos - unequal) - three subsidiary cells are present, with one markedly smaller than the others (shepherd's purse, field pansy, roseroot, thickleaf bergenia)		Tetracytic (Greek tetra - four) - 2 lateral subsidiary cells and 2 polar (terminal) subsidiary cells (most commonly in monocots)
Paracytic (Greek para - beside) - two or four subsidiary cells with their longitudinal axes parallel to the stomatal pore (periwinkle, lingonberry, dill, flax, oats), Gnetales (Ephedra), ferns, horsetails		Actinocytic (Greek aktis - ray) - 5 or more subsidiary cells radially elongated in a radiating pattern (cotton, black pepper)
Encyclocytic (Greek kiklos - circle) - four or more subsidiary cells arranged in a narrow ring.		Staurocytic (Greek stauros - cross) - arranged in a cross-like pattern
Pericytic (from Greek peri - near, around): guard cells are completely surrounded by a single subsidiary Cell (ferns)		Polocytic (from Greek polos - pole): guard cells are surrounded by a single subsidiary cell, though not entirely; one or two ordinary epidermal cells adjoin one of the stomatal poles.

Main morphological types of stomatal complexes in vascular plants

Simple (dermal) hairs provide protection and reduce Transpiration, whereas glandular trichomes secrete various substances. Gas exchange and transpiration are regulated by Stomata.

Trichomes are specialized epidermal outgrowths and projections, including hairs, glands, and emergences.

Epidermal trichomes: 1-11 — simple hairs: 1 — two-horned; 2 — retort-shaped; 3 — T-shaped; 4 — setaceous with a warted cuticle; 5 — whip-shaped with an elongated apical cell; 6 — multicellular, uniseriate, conical with a striate cuticle; 7 — hooked, grappling; 8 — branched; 9 — stellate (top and side views); 10 — vesicular; 11 — papillose; 12-15 — glandular hairs: 12 — with a unicellular stalk and a multicellular HEAD; 13 — with a multicellular uniseriate long stalk and a unicellular small head; 14, 15 — with a multicellular head and a multicellular uni- and multiseriate stalk; 16-21 — emergences: 16 — stinging Hair (a — multicellular pedestal; b — ampulla; c — head); 17 — bristle; 18 — peltate gland; 19, 20 — thorn and prickle.

Emergences are formed with the participation of epidermal cells (hop scales; stem and leaf prickles of wild rose, gooseberry, raspberry, madder; fruit prickles of horse chestnut, datura; gripping bristles of carrot and beggar-ticks fruits).

Nettle emergences (stinging hairs) have a high multicellular pedestal into which the base of an ampulla-shaped living cell with a small head is embedded. The Cell sap contains formic acid, histamine, acetylcholine, toxins, and Enzymes. The Cell wall is mineralized with lime and silica. Upon Touch, the head easily breaks off, the sharp edges pierce the Skin, and a burning sensation is felt.

3. Secretory tissues and structures

4. Mechanical tissues (skeletal or supportive)

Collenchyma

Angular — composed of tightly packed 4-6-angled cells whose walls are thickened only at the corners.

Lamellar — characterized by the thickening of tangential walls parallel to the organ surface.

Lacunar — has intercellular spaces and consists of cells whose walls are thickened more or less evenly.

Sclerenchyma

Sclereids — brachysclereids (found in fruit flesh, pericarp, seed coat, bark, phloem, and pith of axial organs), macrosclereids (columnar), osteosclereids (dumbbell-shaped), astrosclereids (stellate), trichosclereids (branched).

Xylary fibers (libriform fibers) — part of the xylem, providing its strength and hardness.

Phloem fibers (bast fibers) — very long, narrow cells with thickened striated-layered walls.

Pericyclic (perivascular) fibers — formed from the pericycle and located at the periphery of the central cylinder.

Bundle sheath fibers — formed from the procambium.

Cortical fibers — located in the cortex of axial organs in bundles or singly.

5. Conducting tissues

In conducting elements — vessels — the internal wall thickenings appear as rings, spirals, ladders, or nets.

6. Vascular bundles

In plant organs, xylem and phloem accompany each other, forming conducting or vascular-fibrous bundles.

Closed bundles — formed by the procambium, lack cambium, closed, incapable of renewal and growth.

Open bundles — bundles containing cambium, capable of growth and expansion.

Types of vascular bundles

A — collateral closed, B — collateral open, C — bicollateral open, D — concentric with external xylem (centrophloic), E — concentric with internal xylem (centroxylic), F — radial, 1 — phloem, 2 — xylem, 3 — cambium, 4 — external phloem, 5 — internal phloem.

7. Ground tissue (parenchyma)

Ground tissue, or parenchyma, is called packing tissue because it fills the space between other tissues. It is a living tissue that retains meristematic activity.

8. Generalized Classification of Plant Tissues

Meristematic	Primary	Apical forms in the apices, ensuring the longitudinal growth of organs. Intercalary is located at the base of leaves and SHOOT internodes, facilitating their elongation. Lateral are positioned along the axis of organs and cause their radial thickening: - pericycle (forms lateral roots, primary sclerenchyma, and parenchyma) - procambium (forms primary phloem and xylem)
	Secondary	Lateral: - cambium (forms secondary phloem and xylem) - phellogen (forms periderm) Wound or traumatic
Dermal	Primary	Epidermis with stomata (multifunctional) leaves, stems of herbaceous plants. Epidermis without stomata - rhizomes of monocots. Epidermis with root hairs (trichoblasts, atrichoblasts) - roots. Velamen provides protection against mechanical damage and water loss - aerial roots.
	Secondary	Periderm (consisting of phellogen and its derivatives - cork and phelloderm), protects the stems of woody plants, most underground organs, occasionally fruits and other plant parts. Bark (rhytidome, a collection of periderms) secondary or tertiary protective tissue: - scaly bark; - ring bark.
Secretory (excretory)	Exogenous (external secretion)	Glandular hairs, glands, emergences, scales - glandular trichomes. Nectaries, osmophores - produce sugary substances - nectar. Hydathodes - adaptations for guttation - the exudation of weak solutions of mineral and, less commonly, organic substances in droplet form.
	Endogenous (internal secretion)	Idioblast cells - these structures are found in any organs and body parts.
		Laticifers	Articulated:	with anastomoses without anastomoses
			Non-articulated:	branched unbranched
		Receptacles, ducts, canals		Lysigenous - formed by the accumulation of secretion within a single cell that dies and breaks down, while the secretion remains in the resulting cavity. Fruit rinds of citrus plants, elecampane rhizomes.
				Schizogenous - formed by the deposition of secreted substances in intercellular spaces. Examples include resin ducts in conifers; Apiaceae, eucalyptus. Have distinct cavity boundaries.
				Schizo-lysigenous - formed in the intercellular spaces of plants, stems, roots, rhizomes, surrounded by secretory cells capable of division.
Ground	Assimilation (photosynthetic) parenchyma (chlorenchyma)	Palisade - with a high content of METABOLISM/14.html">Chloroplasts ensuring intensive Photosynthesis. Spongy - gas exchange and transpiration take place due to the presence of intercellular spaces. Plicate (folded) - forms the mesophyll of needle-shaped and narrowly lanceolate leaves of certain conifer and flowering plant species.
	Storage contains starch and aleurone grains, and fatty oil.
	Water-storage (hydroparenchyma) is typical for the above-ground organs of hydrophytes, hygrophytes, and succulents.
	Ventilating or aerenchyma is particularly well developed in hydrophytes and hygrophytes.

Last update: 07/08/2026

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