The Root
The root is the usually underground, non-green, descending part of the plant that develops from the radicle.
Types
- Tap root (dicots) - one main root with lateral branches, from the radicle (e.g., mustard).
- Fibrous root (monocots) - a cluster of thin roots from the base of the stem (e.g., wheat).
- Adventitious roots - arise from parts other than the radicle (e.g., grass, banyan, Monstera).
Regions of the root (from the tip upward): root cap -> region of meristematic activity -> region of elongation -> region of maturation (which bears the root hairs).
Modifications of the root
| Function | Modification | Examples |
|---|---|---|
| Storage | swollen tap/adventitious roots | carrot, turnip; sweet potato |
| Support | prop roots | banyan |
| Support | stilt roots | maize, sugarcane, screwpine |
| Respiration | pneumatophores | Rhizophora (mangrove) - grow upward for gas exchange |
| Nitrogen fixation | root nodules | legumes (pea, gram) - house nitrogen-fixing Rhizobium |
The Stem
The stem is the ascending part of the plant that develops from the plumule. It bears nodes and internodes, buds (terminal + axillary), and holds up the leaves, branches and flowers; young stems are usually green.
Modifications of the stem
| Location | Modification | Examples |
|---|---|---|
| Underground (storage/perennation) | rhizome | ginger, turmeric |
| tuber (eyes = axillary buds) | potato | |
| bulb | onion, garlic | |
| corm | Colocasia, gladiolus | |
| Sub-aerial (vegetative propagation) | runner / stolon / offset / sucker | grass / jasmine / water hyacinth / Chrysanthemum |
| Aerial | stem tendrils (from axillary buds) | grapevine, cucumber, pumpkin |
| thorns (axillary, protective) | Citrus, Bougainvillea | |
| phylloclade (flattened green stem) | Opuntia |
[NEET Important] A tendril of a grapevine/cucumber is a stem modification (axillary bud), but a pea tendril is a leaf modification - a classic trap.
Visual - Root & Stem Modifications
Root modifications (fusiform/napiform storage, prop, stilt, pneumatophore) and stem modifications - underground (rhizome, tuber, corm, bulb), subaerial (runner, stolon, offset, sucker) and aerial (tendril, thorn, phylloclade).