NCERT grounding
NCERT Class 11 Biology, Chapter 6 (Anatomy of Flowering Plants), opens §6.1 with the tissue system. After classifying tissues by cell type, the text states that tissues also "vary depending on their location in the plant body," and that "on the basis of their structure and location, there are three types of tissue systems." These are the epidermal, the ground or fundamental, and the vascular or conducting tissue systems. The chapter summary confirms the ground tissue is divided into cortex, pericycle and pith, while the vascular system is "formed by the xylem and phloem."
"There are three types of tissue systems — the epidermal tissue system, the ground or fundamental tissue system and the vascular or conducting tissue system."
NCERT Class 11 Biology · §6.1
The three tissue systems
A tissue system is not a single tissue but a functional grouping defined by position. The three systems run continuously through root, stem and leaf, and the same tissue (say, parenchyma) can belong to different systems depending on where it lies. Reading any section means assigning each ring of cells to one of these three layers — outermost covering, the bulk in between, and the conducting strands.
Orientation: work inward from the surface — the epidermal system is the skin, the ground system is everything in between, and the vascular system is the plumbing embedded within the ground tissue.
Epidermal
Outer covering. Epidermis, cuticle, stomata, trichomes, root hairs.
Protects, limits water loss, regulates gas exchange.
Ground
The bulk. Cortex, pericycle, pith, medullary rays, mesophyll.
Storage, support, and photosynthesis in leaves.
Vascular
Conducting. Xylem + phloem (± cambium) in bundles.
Translocates water, minerals and food.
Epidermal tissue system
The epidermal tissue system forms the outermost covering of the whole plant body. It comprises epidermal cells, stomata, and the epidermal appendages — trichomes and root hairs. The epidermis is the outermost layer of the primary plant body: elongated, compactly arranged cells forming a continuous, usually single-layered sheet. The cells are parenchymatous, with a thin lining of cytoplasm and a large vacuole.
On the aerial surface the epidermis is coated with a waxy cuticle that prevents water loss; crucially, the cuticle is absent in roots, since roots must absorb water. Root epidermal cells instead extend into unicellular root hairs that absorb water and minerals from soil. On the stem, epidermal hairs are called trichomes — usually multicellular, branched or unbranched, soft or stiff, sometimes secretory, and helping reduce transpiration.
Stomata and the stomatal apparatus
Stomata are pores in the epidermis of leaves that regulate transpiration and gaseous exchange. Each stoma is bounded by two guard cells. In most plants these are bean (kidney) shaped; in grasses they are dumb-bell shaped. Whatever the shape, the outer wall (away from the pore) is thin and the inner wall (toward the pore) is highly thickened — this differential thickening is what bows the cells outward when turgid and opens the pore. Guard cells possess chloroplasts and so control opening and closing. Where neighbouring epidermal cells become specialised in shape and size around the guard cells, they are called subsidiary cells.
Figure 1. The stomatal apparatus = pore + two guard cells + surrounding subsidiary cells. The inner wall (toward the pore) is thickened; the outer wall is thin. Grass guard cells are dumb-bell shaped rather than bean shaped.
Ground (fundamental) tissue system
All tissues except the epidermis and the vascular bundles constitute the ground tissue. It is made of the simple tissues — parenchyma, collenchyma and sclerenchyma. Parenchymatous cells fill the cortex, pericycle, pith and medullary rays of primary stems and roots. In leaves, the ground tissue is the chloroplast-rich mesophyll that performs photosynthesis. The ground system forms the main bulk of the plant body and is the great reservoir for storage and support.
Memory hook: the ground system is "everything in the middle" — if a region is neither the skin nor a conducting strand, it is ground tissue.
Cortex
Several layers of thin-walled parenchyma between epidermis and pericycle, with intercellular spaces. Innermost layer is the endodermis.
Pericycle
Layer(s) just inside the endodermis. In roots it initiates lateral roots and vascular cambium during secondary growth.
Pith & rays
Central parenchyma (pith) and radial medullary rays. Pith is large in monocot roots, small or absent in dicot roots.
Mesophyll
Leaf ground tissue: palisade (elongated, adaxial) and spongy (loose, abaxial) parenchyma; chloroplast-rich.
Vascular (conducting) tissue system
The vascular system consists of the two complex tissues — xylem (conducts water, mineral salts, some organic nitrogen and hormones upward) and phloem (translocates food, bidirectionally, on a source–sink basis). Together they form vascular bundles. In dicot stems a strip of cambium lies between phloem and xylem; because cambium can cut off secondary xylem and phloem, such bundles are called open. In monocots no cambium is present, no secondary tissue forms, and the bundles are closed.
Bundles are also classified by the relative position of xylem and phloem. When xylem and phloem lie on different radii in an alternate manner, the arrangement is radial — characteristic of roots. When they lie together along the same radius, the bundle is conjoint — typical of stems and leaves, with phloem usually on the outer side of the xylem (collateral). A bundle with phloem on both sides of xylem is bicollateral.
Figure 2. Radial bundles (roots) place xylem and phloem on alternate radii. Conjoint bundles place them on the same radius; closed (monocot stem) lacks cambium, open (dicot stem) has a cambium strip and can grow secondarily.
Open
Dicot stem
cambium present
- Cambium lies between xylem and phloem
- Forms secondary xylem and phloem
- Allows secondary growth
- Bundles arranged in a ring
Closed
Monocot stem
cambium absent
- No cambium between xylem and phloem
- No secondary tissue formed
- No secondary growth (e.g. grasses)
- Bundles scattered, with bundle sheath
A diagnostic feature: bulliform cells
In grass leaves, certain adaxial (upper) epidermal cells along the veins become large, empty and colourless — these are bulliform cells. When turgid (well-watered), the leaf surface stays exposed; when flaccid under water stress, they make the leaf curl inwards to minimise water loss. They are a favourite NEET single-fact question and a clean indicator of monocot (grass) leaf identity.
Tissue systems, one rule
Every section reduces to epidermal (skin), ground (bulk: cortex–pericycle–pith / mesophyll) and vascular (xylem + phloem bundles). Master these three and any T.S. becomes readable.
Worked examples
A transverse section shows scattered vascular bundles, each surrounded by a sclerenchymatous bundle sheath; the bundles are conjoint and closed and the phloem parenchyma is absent. Identify the organ.
Scattered closed bundles with sclerenchymatous bundle sheath and absent phloem parenchyma are the textbook signature of the monocot stem. "Closed" tells you there is no cambium, hence no secondary growth — consistent with grasses.
In a root, xylem and phloem are found on alternate radii rather than together on one radius. What is this bundle arrangement called, and why does it suit a root?
This is a radial arrangement. Placing xylem and phloem on separate radii lets absorbed water enter xylem directly along the shortest path, and is characteristic of roots. (In stems and leaves the bundles are conjoint instead.)
Name the structure that consists of the stomatal aperture, the two guard cells and the surrounding specialised epidermal cells taken together.
The stomatal apparatus. The specialised epidermal cells around the guard cells are the subsidiary cells; the guard cells have a thin outer wall, a thick inner wall, and chloroplasts.