stams

A stem has many functions. One of its functions is to support the flowers, leaves and fruits. Stems also keep the plant upright. Some plants can store food in their stems. The stem transports water and food throughout the plant.

The stems of trees are called trunks and trunks contain a lot of wood. Trees and plants that contain a lot of wood in their stems are called woody plants. Wood gives the plant its strength. Plants that have no wood (or only very little) are called herbaceous plants (like herbs). These plants get their strength from the pressure of water.

The petiole is the stalk that attaches the leaf to the stem. The petiole is part of the leaf (see section 6.4). The places where the petioles are attached to the stem are called nodes. An axillary bud is found in the space between a leaf and the stem. New leaves will grow out of axillary buds. Sometimes side branches or flowers grow out of axillary buds. The part of the stem between two nodes is called the internode. At the end of the stem you will also find a bud.

This is the terminal bud. Out of this bud a new piece of stem will grow. In winter you can see leaf scars on the stem. The leaf scars are where the petioles were attached to the stem during the growing season.

You have a circulatory system made up of blood vessels, which transports oxygen and nutrients throughout your body. You learned that plants also have their own kind of circulatory system. In plants, water and food are transported through specialised vessels: the xylem and phloem vessels. The xylem of a plant is the system of tubes and vessels that circulates water and dissolved minerals in a plant from the roots to the food-producing leaves.

Once water has entered the stem of the plant, via the roots, how does it get to the top? Is it pushed up the stem or is it pulled up? It is both! Just as in roots, water enters the stem through the process of osmosis. Water enters the stem through osmosis and pushes the water inside the xylem vessels upwards. This is possible because water sticks to the walls of the xylem vessels. It is also pulled up into the vessels because water evaporates from the leaves.

The phloem vessels are found throughout the entire plant, transporting the glucose and other substances made by the plant to the parts that use the food. The xylem and phloem vessels are organised in bundles, the vascular bundles.