While Morphology was about the “exterior,” Anatomy is about the “engine” under the hood. It’s the study of internal tissues and how they are organized to transport water, nutrients, and provide structural support.

The Internal Engine: Mastering Anatomy of Flowering Plants

To understand how a tree grows for hundreds of years or how a leaf breathes, we have to look inside. Plant anatomy is governed by Tissues—groups of cells with a common origin and function.

In this chapter, we explore the difference between young, dividing cells and mature, specialized cells, and we uncover the secret of “Secondary Growth”—the process that turns a soft green stem into hard, solid wood.

The Core Pillars of Plant Anatomy

1. Meristematic vs. Permanent Tissues

• Meristems: The “forever young” cells that divide continuously. We have Apical (growth in length), Intercalary (regrowing grass eaten by herbivores), and Lateral (growth in girth).
• Permanent Tissues: Cells that have stopped dividing and taken on a specific role.
  • Simple: Parenchyma (storage), Collenchyma (flexible support), and Sclerenchyma (dead, hard support).
  • Complex: Xylem (water transport) and Phloem (food transport).

2. The Tissue System

Plants have three main systems:

• Epidermal: The “skin,” including the cuticle, stomata, and root hairs.
• Ground: The “bulk” of the plant (cortex, pericycle, pith).
• Vascular: The “plumbing” (Xylem and Phloem).

3. Dicot vs. Monocots (The Internal Map)

• Roots: Dicots have few xylem bundles (2-4); Monocots have many (Polyarch).
• Stems: Dicots have vascular bundles arranged in a ring; Monocots have them scattered throughout the ground tissue.
• Leaves: Dicots have “Dorsiventral” leaves (different top and bottom); Monocots have “Isobilateral” leaves (both sides look the same).

4. Secondary Growth

This is why a sunflower stays thin while an oak tree gets wider. It happens due to the activity of the Vascular Cambium and Cork Cambium. It results in the formation of Wood (Secondary Xylem) and Bark.

The Gauntlet: 10 Challenging Aptitude Questions

Question 1: The Regenerating Grass

When a cow eats the top of a grass blade, the grass grows back rapidly. Which specific meristem is responsible for this regeneration?

Question 2: The “Dead” Support

Sclerenchyma is a permanent tissue that is dead at maturity. Name its two types and identify which one provides the “grittiness” found in the fruit pulp of pears and sapotas.

Question 3: The Stomatal Guardian

In Dicot leaves, guard cells are bean-shaped. What is the shape of guard cells in Monocots (Grasses)?

Question 4: Radial vs. Conjoint

In Roots, xylem and phloem are arranged on different radii. What is this arrangement called? Compare it to the arrangement found in Stems.

Question 5: The Casparian Strip

In the endodermis of roots, there is a water-impermeable, waxy material deposited in the form of strips. What is this material called, and what is its physiological purpose?

Question 6: Open vs. Closed Bundles

Why are vascular bundles in Dicot stems called “Open,” while those in Monocot stems are called “Closed”? Hint: Think about the potential for secondary growth.

Question 7: Heartwood vs. Sapwood

As a tree ages, the central part of the stem becomes dark brown, hard, and resistant to insects. What is this region called, and does it still conduct water?

Question 8: The Bulliform Advantage

In Monocot leaves, certain epidermal cells along the veins become large, empty, and colorless. What are these cells called, and how do they help the leaf during water stress?

Question 9: Spring Wood vs. Autumn Wood

In temperate regions, the cambium is more active in spring than in winter. How does this difference in activity create “Annual Rings,” and can we use them to tell a tree’s age?

Question 10: The Bark Mystery

“Bark” is a non-technical term used to describe all tissues exterior to the vascular cambium. Name the tissues included in “Bark.”

Detailed Explanations & Solutions

1. Regenerating Grass

Result: Intercalary Meristem. (It is located between mature tissues).

2. The “Dead” Support

The two types are Fibres and Sclereids.

Result: Sclereids (specifically stone cells) provide the grit in pears.

3. Stomatal Guardian

Result: Dumb-bell shaped.

4. Radial vs. Conjoint

• Roots = Radial (Xylem and Phloem are separate).
• Stems = Conjoint (Xylem and Phloem are together on the same radius).Result: Radial in roots; Conjoint in stems.

5. Casparian Strip

The material is Suberin.

Result: It forces water to move through the living cells of the endodermis rather than around them, acting as a check-post.

6. Open vs. Closed

Dicot bundles have Cambium between xylem and phloem (Open to secondary growth). Monocot bundles lack cambium (Closed to secondary growth).

Result: Presence of Cambium makes it “Open.”

7. Heartwood vs. Sapwood

The central part is Heartwood.

Result: It does NOT conduct water; it provides mechanical support. Sapwood is the outer region that handles water transport.

8. Bulliform Advantage

These are Bulliform Cells. When they lose water (flaccid), they cause the leaf to curl inwards.

Result: This reduces the exposed surface area and minimizes water loss.

9. Annual Rings

Spring wood has wider vessels (lighter color); Autumn wood has narrow vessels (darker color).

Result: One light ring + one dark ring = One year of growth (Dendrochronology).

10. Bark Mystery

Bark includes the Periderm (phellogen, phellem, and phelloderm) and Secondary Phloem.

Result: Everything outside the vascular cambium.

Pro-Tip: The “Root-Stem” Distinction

If you are looking at a cross-section under a microscope:

• Protoxylem towards the center (Endarch): It’s a Stem.
• Protoxylem towards the periphery (Exarch): It’s a Root.