Plant tissues are organised into three fundamental tissue systems that run continuously throughout the plant body. The dermal tissue system: forms the outer protective covering (epidermis of primary plant body; periderm/bark in secondary growth). The vascular tissue system: transports water, minerals, and organic nutrients through xylem and phloem. The fundamental (ground) tissue system: all tissues that are neither dermal nor vascular — includes parenchyma, collenchyma, and sclerenchyma. Understanding the specific tissues within these systems and their precise locations in root, stem, and leaf cross-sections is essential for NEET plant anatomy questions. The stele (central vascular cylinder) consists of pericycle, vascular bundles, and pith.

Conjunctive tissue is the parenchymatous tissue (ground tissue) located between the xylem and phloem in the stele of a root. In a monocot root cross-section: the vascular bundles are arranged in a ring, with alternating xylem and phloem bundles. The tissue between adjacent xylem and phloem bundles is conjunctive tissue (parenchyma). In a dicot root: radial vascular bundles alternate with phloem bundles; conjunctive tissue fills the spaces between them. In some descriptions: conjunctive tissue may also refer to the ground tissue in stems that fills the space between vascular bundles. The term 'conjunctive' (from Latin 'coniungere' = to join) refers to the fact that it joins or fills the spaces between the vascular tissue components.

Casparian strips are bands of suberin (a waxy, hydrophobic polymer) deposited in the radial and transverse walls of endodermal cells — they form a complete band around each endodermal cell. Location: exactly in the cell walls of the endodermis (the innermost layer of the root cortex). They do NOT occur in the inner and outer tangential walls — only in the radial and transverse walls, creating a seal. Function: the Casparian strip is hydrophobic and impermeable to water — it blocks the apoplastic pathway (water flow through cell walls) at the endodermis. Water and dissolved solutes moving apoplastically must cross the plasma membrane of endodermal cells to enter the stele. This gives the endodermis selective control over what enters the vascular system. Named after Robert Caspary (1865). Suberin deposition = suberin lamellae (in all walls of passage cells) in older endodermis.

Subsidiary cells (also called accessory cells) are specialised epidermal cells that are located immediately adjacent to guard cells, surrounding the stomatal apparatus. They are functionally and structurally associated with guard cells and assist in stomatal movement. Subsidiary cells are clearly defined in certain stomatal types: Paracytic (Rubiaceous) type: 2 subsidiary cells parallel to guard cells. Diacytic (Caryophyllaceous) type: 2 subsidiary cells perpendicular to guard cells. Anisocytic (Cruciferae) type: 3 subsidiary cells of unequal size. Anomocytic (Ranunculaceous) type: no distinct subsidiary cells. Tetracytic type: 4 subsidiary cells. Gramineous type: 4 subsidiary cells, 2 lateral (narrow) + 2 terminal (dome-shaped). In grasses: dumbbell-shaped guard cells + subsidiary cells create specialised stomatal complex. Subsidiary cells contribute to stomatal movement by providing a sink for K⁺ and water ions when guard cells open/close.

In many dicot stems, the innermost layer of the cortex (corresponding to the endodermis of the root) is called the starch sheath because its cells contain abundant starch grains in their plastids. This layer is also called the endodermis of the stem. In roots, the same layer is the endodermis with Casparian strips. In stems, the endodermal cells often do not have well-developed Casparian strips but instead are characterised by their starch content. The starch grains in these cells act as statoliths (gravity-sensing organelles) — when the stem is tilted, statoliths sediment to the lower side of the cell → this asymmetry triggers the gravitropic response → stem bends upward (negative geotropism). This starch sheath layer is therefore involved in both storage and graviperception in stems.

Dicot root (e.g., mustard, bean): epidermis (with root hairs), cortex (parenchyma), endodermis (with Casparian strips), pericycle (1-2 layers), 2-6 xylem bundles (exarch — protoxylem toward outside), 2-6 phloem bundles alternating with xylem, conjunctive tissue between xylem and phloem, pith (small or absent). Secondary growth: lateral roots from pericycle, vascular cambium forms between xylem and phloem → secondary xylem and phloem. Monocot root (e.g., maize): epidermis, extensive cortex, endodermis with Casparian strips (often also with suberin lamellae), pericycle (single layer), many xylem bundles (>6), phloem bundles alternating, large pith (parenchymatous). No secondary growth. Polyarch arrangement (many vascular bundles).

The epidermis is the outermost layer of cells in primary plant organs, covered by a waxy cuticle (cutin polymer). Epidermis functions: protection from water loss, mechanical damage, pathogens. Components: epidermal cells (flat, interlocking), guard cells (paired, bean-shaped in dicots; dumbbell-shaped in grasses), subsidiary cells (adjacent to guard cells), trichomes (hair-like epidermal outgrowths — unicellular or multicellular, branched or unbranched). Stomatal distribution: amphistomatic leaf (stomata both surfaces), hypostomatous (stomata only on lower surface — most dicots), epistomatous (stomata only on upper surface — some aquatics like water lily). Stomatal density: typically 100-700 stomata/mm² (higher in more active photosynthetic surfaces). Hydathodes: stomata at leaf margins for guttation (not regulated — always open).

Secondary growth in stems and roots produces wood (secondary xylem) and bark. Vascular cambium: forms between primary xylem and phloem (fascicular cambium from procambium, interfascicular cambium from parenchyma). Produces secondary xylem (wood) inward and secondary phloem outward. Annual rings: in temperate trees — spring wood (early wood: wide vessels, less dense) vs autumn wood (late wood: narrow vessels, dense). Cork cambium (phellogen): forms in the cortex → produces cork (phellem, outward) and phelloderm (inward). Cork cells: dead, suberised, impermeable to water. Cork + phelloderm + phellogen = periderm. Bark = periderm + secondary phloem (outside the vascular cambium). Lenticels: loose areas in the cork with intercellular spaces → allow gas exchange in bark. Heartwood vs sapwood: inner, darker heartwood = dead xylem filled with resins, tannins. Outer, lighter sapwood = functional xylem conducting water.