A stem grows from the plumule and bears leaves at its nodes, with internodes between. Buds sit at the tip and in the leaf axils. Stems carry water and food. Some stems store food, climb, defend the plant, make food or spread it.
about 25 min1 simulation1 practice question1 Python program5 questions to check yourself
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The stem begins as the plumule
The other end of the embryo holds a small bud, the plumule. It grows upwards into the stem. The stem is the ascending part of the plant. It bears branches, leaves, flowers and fruits. A young stem is green. Later it often turns woody and dark brown.
A stem has several jobs.
It holds up the branches that bear leaves, flowers and fruits.
It conducts water and minerals from the roots to the leaves. It also carries the food made in the leaves to the other parts.
Some stems also store food, give support, protect the plant or help it spread.
Nodes, internodes and buds
A node is the place on the stem where a leaf is attached.
An internode is the part of the stem between two nodes.
A bud in the angle between a leaf and the stem is an axillary bud. It can grow into a branch or a flower.
The bud at the tip of the stem or of a branch is the terminal bud. It makes the stem grow longer.
A twig with three nodes and the internodes between them. A leaf is attached at each node, and a small axillary bud sits in the angle between each leaf and the stem. The terminal bud sits at the tip of the twig. One internode is marked with a double arrow.
Add nodes, and the stem gets one more internode each time. Lengthen the internodes, and the stem between the first and the last node gets longer.
Try it in Python
The program lists seven stems with a special job, and groups the plants by what the stem does.
Practise with new numbers
Stems with special jobs
Underground stems. Potato, ginger, turmeric, zaminkand (Amorphophallus) and colocasia have stems that grow underground. They are stems because they have nodes and buds. The eyes of a potato are buds at its nodes.
These stems store food. They are also organs of perennation. This means they carry the plant through a season that is bad for growth, such as a dry or a cold season. They can also grow into new plants, which is vegetative propagation.
Stems above the ground.
Stem tendrils. A stem tendril is slender and spirally coiled. It helps a plant to climb. Cucumber, pumpkin, watermelon and grapevine have stem tendrils.
Thorns. An axillary bud may change into a woody, straight and pointed thorn. Thorns protect the plant from animals that browse. Citrus and Bougainvillea have thorns.
Flattened or fleshy stems. Plants of dry places, such as Opuntia and Euphorbia, have green stems with chlorophyll. The stem makes the food. In Opuntia the stem is flat, and the leaves are spines.
Stems that spread the plant.
Runner. A slender stem creeps along the ground, as in grass and strawberry. It spreads the plant to new places.
Stolon. A slender branch grows from the base of the stem, grows above the ground for a while, and then arches down to touch the soil. Mint and jasmine have stolons.
Offset. A short branch has short internodes. Each node bears a rosette of leaves and a tuft of roots. Water plants such as Pistia and Eichhornia have offsets.
Common mistakes
Calling a potato a root. It has nodes and buds, so it is a stem.
Mixing up node and internode. The node is the place where the leaf is attached. The internode is the stretch between two nodes.
Saying a thorn comes from a leaf. In Citrus and Bougainvillea it comes from an axillary bud.
**Thinking the flat pad of Opuntia is a leaf.** It is a flattened stem, and the leaves are spines.
Remember these
Stem from the plumule. Node: where a leaf is attached. Internode: 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.