How to Tell a Maize Stem From a Sunflower Stem Under a Microscope
Relate the parts of the epidermal tissue system to their functions, distinguish ground and vascular tissue systems and types of vascular bundles, and compare the internal structure of dicot and monocot roots, stems and leaves.
What does the inside of a plant look like?
Cut a thin slice across a sunflower stem and a maize stem and look under a microscope, and the patterns inside are strikingly different. The arrangement of tissues tells you at a glance whether a plant is a dicot or a monocot.
This part covers the epidermal tissue system, ground and vascular tissue systems, root anatomy, and stem and leaf anatomy.
This part covers the epidermal tissue system, ground and vascular tissue systems, root anatomy, and stem and leaf anatomy.
What makes up the epidermal tissue system, and what does each part do?
The epidermal tissue system forms the outer covering of the plant and includes epidermal cells, a waxy cuticle, stomata with guard and subsidiary cells, and outgrowths such as root hairs and trichomes — each protecting the plant or controlling exchange with the air and soil.
- Epidermal cells — usually one layer of elongated, tightly packed cells with a large vacuole
- Cuticle — a waxy layer over the epidermis that reduces water loss; absent in roots
- Stomata — pores that control transpiration and gas exchange; each is bordered by two guard cells, bean-shaped in most plants but dumb-bell shaped in grasses; guard cells contain chloroplasts
- Subsidiary cells — specialised epidermal cells around the guard cells; together with the pore and guard cells they make the stomatal apparatus
- Root hairs — single-celled extensions of root epidermal cells that absorb water and minerals
- Trichomes — hairs on the stem, often multicellular, branched or unbranched, sometimes secretory; they help reduce water loss
An everyday example. The itchy feel of lady's finger (bhindi) plants comes from their trichomes.
The substance. Roots have no cuticle — it would block the very absorption of water that roots exist for.
- Epidermal cells — usually one layer of elongated, tightly packed cells with a large vacuole
- Cuticle — a waxy layer over the epidermis that reduces water loss; absent in roots
- Stomata — pores that control transpiration and gas exchange; each is bordered by two guard cells, bean-shaped in most plants but dumb-bell shaped in grasses; guard cells contain chloroplasts
- Subsidiary cells — specialised epidermal cells around the guard cells; together with the pore and guard cells they make the stomatal apparatus
- Root hairs — single-celled extensions of root epidermal cells that absorb water and minerals
- Trichomes — hairs on the stem, often multicellular, branched or unbranched, sometimes secretory; they help reduce water loss
An everyday example. The itchy feel of lady's finger (bhindi) plants comes from their trichomes.
The substance. Roots have no cuticle — it would block the very absorption of water that roots exist for.
How do the ground and vascular tissue systems differ, and how are vascular bundles classified?
The ground tissue system includes all tissues except the epidermis and vascular bundles, while the vascular tissue system is made of xylem and phloem arranged in vascular bundles, which are radial, conjoint, open or closed depending on how xylem, phloem and cambium lie.
Ground tissue. Parenchyma, collenchyma and sclerenchyma forming the cortex, pericycle, pith and medullary rays of stems and roots; in leaves it is the mesophyll, thin-walled cells full of chloroplasts.
Vascular bundles:
- Radial — xylem and phloem on different radii, alternating around the centre: roots
- Conjoint — xylem and phloem on the same radius, usually with phloem outside: stems and leaves
- Open — cambium present between xylem and phloem, so secondary growth is possible: dicot stems
- Closed — no cambium: monocot stems
An everyday example. The tough strings you chew out of sugarcane are its many vascular bundles, scattered through the stem.
The substance. Only open bundles allow secondary growth, which is why most monocots cannot thicken their stems the way woody dicots do.
Ground tissue. Parenchyma, collenchyma and sclerenchyma forming the cortex, pericycle, pith and medullary rays of stems and roots; in leaves it is the mesophyll, thin-walled cells full of chloroplasts.
Vascular bundles:
- Radial — xylem and phloem on different radii, alternating around the centre: roots
- Conjoint — xylem and phloem on the same radius, usually with phloem outside: stems and leaves
- Open — cambium present between xylem and phloem, so secondary growth is possible: dicot stems
- Closed — no cambium: monocot stems
An everyday example. The tough strings you chew out of sugarcane are its many vascular bundles, scattered through the stem.
The substance. Only open bundles allow secondary growth, which is why most monocots cannot thicken their stems the way woody dicots do.
How do dicot and monocot roots compare in transverse section?
Both roots have an epidermis with root hairs, a parenchymatous cortex, an endodermis with Casparian strips, a pericycle and radial vascular bundles, but dicot roots usually have two to four xylem arches and a small pith, while monocot roots have more than six xylem arches and a large pith.
From outside in:
- Epiblema — outer epidermis bearing root hairs
- Cortex — several layers of thin-walled parenchyma with air spaces
- Endodermis — the innermost cortical layer of barrel-shaped cells with no gaps; their walls carry waxy Casparian strips of suberin that block water from passing between cells
- Pericycle — thick-walled parenchyma where lateral roots and, in dicots, cambium arise
- Vascular bundles — radial, with parenchyma (conjunctive tissue) between xylem and phloem
- Stele — everything inside the endodermis
Dicot versus monocot root:
- Xylem arches: two to four versus more than six
- Pith: small or absent versus large and well developed
- Secondary growth: occurs versus absent
An everyday example. A young maize root is a monocot root, with many xylem patches around a wide central pith.
The substance. Casparian strips force water to pass through living cell membranes, letting the root control what enters the vascular tissue.
From outside in:
- Epiblema — outer epidermis bearing root hairs
- Cortex — several layers of thin-walled parenchyma with air spaces
- Endodermis — the innermost cortical layer of barrel-shaped cells with no gaps; their walls carry waxy Casparian strips of suberin that block water from passing between cells
- Pericycle — thick-walled parenchyma where lateral roots and, in dicots, cambium arise
- Vascular bundles — radial, with parenchyma (conjunctive tissue) between xylem and phloem
- Stele — everything inside the endodermis
Dicot versus monocot root:
- Xylem arches: two to four versus more than six
- Pith: small or absent versus large and well developed
- Secondary growth: occurs versus absent
An everyday example. A young maize root is a monocot root, with many xylem patches around a wide central pith.
The substance. Casparian strips force water to pass through living cell membranes, letting the root control what enters the vascular tissue.
How do dicot and monocot stems and leaves differ in transverse section?
A dicot stem has a ring of conjoint, open bundles around a large pith, while a monocot stem has many scattered, closed bundles each wrapped in a sclerenchyma sheath with no distinct pith; dicot leaves have mesophyll split into palisade and spongy layers (dorsiventral), while grass leaves have undifferentiated mesophyll (isobilateral).
Dicot stem (sunflower):
- Epidermis with cuticle and trichomes; collenchymatous hypodermis
- Endodermis rich in starch (starch sheath)
- Patches of sclerenchyma in the pericycle above the phloem
- Vascular bundles in a ring, conjoint and open, separated by medullary rays
- Large pith
Monocot stem (maize):
- Sclerenchymatous hypodermis
- Many scattered bundles, conjoint and closed, each with a sclerenchyma bundle sheath; smaller bundles near the edge
- Water-containing cavities in the bundles; no distinct pith
Leaves:
- Dorsiventral (dicot) — upper palisade cells, elongated and packed side by side; lower spongy cells, loosely arranged with large air spaces
- Isobilateral (grasses) — mesophyll not divided into palisade and spongy layers
- Veins carry vascular bundles surrounded by bundle sheath cells
- Grasses have large, colourless bulliform cells in the upper epidermis
An everyday example. Rice and wheat leaves curl inwards on very hot afternoons, when their bulliform cells lose water and go limp, reducing water loss.
The substance. Scattered closed bundles and no pith mean monocot stem — but a large pith means monocot root, so always check which organ you are looking at.
Dicot stem (sunflower):
- Epidermis with cuticle and trichomes; collenchymatous hypodermis
- Endodermis rich in starch (starch sheath)
- Patches of sclerenchyma in the pericycle above the phloem
- Vascular bundles in a ring, conjoint and open, separated by medullary rays
- Large pith
Monocot stem (maize):
- Sclerenchymatous hypodermis
- Many scattered bundles, conjoint and closed, each with a sclerenchyma bundle sheath; smaller bundles near the edge
- Water-containing cavities in the bundles; no distinct pith
Leaves:
- Dorsiventral (dicot) — upper palisade cells, elongated and packed side by side; lower spongy cells, loosely arranged with large air spaces
- Isobilateral (grasses) — mesophyll not divided into palisade and spongy layers
- Veins carry vascular bundles surrounded by bundle sheath cells
- Grasses have large, colourless bulliform cells in the upper epidermis
An everyday example. Rice and wheat leaves curl inwards on very hot afternoons, when their bulliform cells lose water and go limp, reducing water loss.
The substance. Scattered closed bundles and no pith mean monocot stem — but a large pith means monocot root, so always check which organ you are looking at.
Exam tip
What earns full marks on plant anatomy?
In diagram questions, check three things in order — the organ (root, stem or leaf), the arrangement of vascular bundles, and the presence and size of pith.
- Epidermis: cuticle, stomata with guard and subsidiary cells, trichomes, root hairs
- Bundles: radial in roots; conjoint in stems and leaves; open in dicot stems; closed in monocot stems
- Roots: dicot 2–4 xylem arches, small pith; monocot more than 6, large pith; Casparian strips in endodermis
- Stems: dicot ring of bundles and large pith; monocot scattered bundles with sheaths, no pith
- Leaves: dorsiventral dicot with palisade and spongy mesophyll; isobilateral grass with bulliform cells
The trap. Assuming large pith always means dicot. Monocot roots have a large pith, while monocot stems have none.
- Epidermis: cuticle, stomata with guard and subsidiary cells, trichomes, root hairs
- Bundles: radial in roots; conjoint in stems and leaves; open in dicot stems; closed in monocot stems
- Roots: dicot 2–4 xylem arches, small pith; monocot more than 6, large pith; Casparian strips in endodermis
- Stems: dicot ring of bundles and large pith; monocot scattered bundles with sheaths, no pith
- Leaves: dorsiventral dicot with palisade and spongy mesophyll; isobilateral grass with bulliform cells
The trap. Assuming large pith always means dicot. Monocot roots have a large pith, while monocot stems have none.
Did you know
Why isn't a banana plant's trunk made of wood?
A banana plant can grow taller than a person, yet a strong push can snap its "trunk" — because it is not a woody stem at all.
Banana is a monocot, and its vascular bundles are closed, with no cambium to produce wood. What looks like a trunk is a pseudostem — a tight roll of long leaf bases wrapped around each other, stiffened mainly by water pressure in their cells.
The true stem stays short and mostly underground, sending up this column of leaf sheaths — anatomy explaining why a banana plant never becomes a timber tree.
Banana is a monocot, and its vascular bundles are closed, with no cambium to produce wood. What looks like a trunk is a pseudostem — a tight roll of long leaf bases wrapped around each other, stiffened mainly by water pressure in their cells.
The true stem stays short and mostly underground, sending up this column of leaf sheaths — anatomy explaining why a banana plant never becomes a timber tree.
Exam relevance
How is plant anatomy tested in NEET?
Anatomy of Flowering Plants is part of the Structural Organisation in Plants and Animals unit of NEET Biology, and it is often tested through diagrams.
What gets asked. Identifying transverse sections of dicot and monocot roots, stems and leaves, types of vascular bundles, the role of Casparian strips and the pericycle, stomatal apparatus, bulliform cells, and dorsiventral versus isobilateral leaves.
Question types. Diagram-based questions, match-the-column lists and statement-based questions.
The trap that costs marks. Mixing up radial and conjoint bundles between roots and stems.
What gets asked. Identifying transverse sections of dicot and monocot roots, stems and leaves, types of vascular bundles, the role of Casparian strips and the pericycle, stomatal apparatus, bulliform cells, and dorsiventral versus isobilateral leaves.
Question types. Diagram-based questions, match-the-column lists and statement-based questions.
The trap that costs marks. Mixing up radial and conjoint bundles between roots and stems.
Key takeaways
What must you be able to do from this part?
- Epidermal system: cuticle reduces water loss; stomatal apparatus of pore, guard cells and subsidiary cells; dumb-bell guard cells in grasses; root hairs absorb, trichomes protect
- Ground and vascular systems: cortex, pericycle, pith, mesophyll; radial, conjoint, open and closed bundles
- Roots: dicot with 2–4 xylem arches and small pith; monocot with more than 6 and large pith; Casparian strips in endodermis
- Stems and leaves: sunflower with a ring of open bundles; maize with scattered closed bundles; dorsiventral dicot leaf versus isobilateral grass leaf
A section shows scattered vascular bundles with sclerenchyma sheaths and no pith. Name the organ and plant group, and give two more features you would expect.
- Ground and vascular systems: cortex, pericycle, pith, mesophyll; radial, conjoint, open and closed bundles
- Roots: dicot with 2–4 xylem arches and small pith; monocot with more than 6 and large pith; Casparian strips in endodermis
- Stems and leaves: sunflower with a ring of open bundles; maize with scattered closed bundles; dorsiventral dicot leaf versus isobilateral grass leaf
A section shows scattered vascular bundles with sclerenchyma sheaths and no pith. Name the organ and plant group, and give two more features you would expect.