Root, Stem and Leaf: Quick Revision

A brief note on Root, Stem and Leaf. Read it before a test. Try each question at the end before you open its answer.

The root

• Tap root system: a primary root from the radicle, with lateral roots (dicots). Fibrous root system: many thin roots from the base of the stem (monocots). Adventitious roots grow from parts other than the radicle.
• Root tip, from the tip upwards: root cap, region of meristematic activity, region of elongation, region of maturation with root hairs.
• Modified roots: storage (carrot, turnip, radish, sweet potato), support (prop roots of banyan, stilt roots of maize and sugarcane) and breathing (pneumatophores of Rhizophora).

The stem

• Node: where a leaf is attached. Internode: the stem between two nodes.
• Axillary bud: in the angle between a leaf and the stem. Terminal bud: at the tip, makes the stem longer.
• Underground stems store food and help perennation: potato, ginger, turmeric, zaminkand, colocasia.
• Aerial stems: tendrils (cucumber) climb, thorns (Citrus) protect, flat stems (Opuntia) make food.
• Spreading stems: runner (grass, strawberry), stolon (mint, jasmine), offset (Pistia, Eichhornia).

The leaf

• Parts: leaf base (stipules, sheath or pulvinus), petiole, lamina with midrib and veins.
• Venation: reticulate in dicots, parallel in monocots.
• Simple leaf: the cuts do not reach the midrib. Compound leaf: the cuts reach the midrib. Pinnate: leaflets on a rachis (neem). Palmate: leaflets at one point (silk cotton).
• Phyllotaxy: alternate, opposite or whorled.
• Special leaves: tendrils (pea), spines (cactus), fleshy leaves (onion, garlic), phyllodes (Australian acacia), traps (pitcher plant, Venus flytrap).

A worked example

A plant has a leaf with many leaflets on a common axis. Its stem has a bud in the axil of the leaf stalk, and the roots are one main root with branches.

1. Leaflets on a common axis. The leaf is pinnately compound, like neem.
2. A bud in the axil of the stalk. The stalk belongs to a leaf, not to a leaflet.
3. One main root with branches. It is a tap root system, so the plant is most likely a dicot.

Practice with new numbers

A program to try

The program lists five modified roots and the job each one does.

Mistakes to avoid

• Calling a potato a root. It is an underground stem with nodes and buds.
• Putting root hairs in the root cap. They are in the region of maturation.
• **Saying a thorn of Citrus comes from a leaf.** It comes from an axillary bud.
• Counting leaflets as leaves. Only a leaf has a bud in its axil.

Check yourself

1. Which region of a root tip makes the root longer?

2. Name the stem of a plant that creeps along the ground and spreads it, as in grass.

3. What kind of venation do monocot leaves have?

4. What is the arrangement of leaves when more than two leaves grow at one node?