Stems

How Stems Support Plants

Stems support the leaves so they can absorb sunlight through photosynthesis and store energy. Stems also support flowers and fruits. Stems stay strong and rigid enough to support these plant parts through processes at the cellular level. 

Like all living things, plants are made of cells. In plants, as in humans, these cells form tissues, which then form organs (leaves, stems, and roots). Stems have bundles of fibrous cells that are long and flexible, allowing them to stay strong while bending in the wind. 

Another way cells in the stem support the plant is turgor pressure, when a plant’s cells fill up with water and push out on their cell walls, making the whole cell rigid. The combined strength and pressure of the water in the cells help keep the plant upright and strong. This is especially important for plants, like tomato plants, that don’t have woody stems. You can often tell when a plant needs water because it starts to wilt. Then, if the plant gets more water through its roots, the stem delivers it to the empty cells so they can fill up and make the plant strong again. 

Transporting Food, Water, and Nutrients to the Cells

All the plant’s cells need energy to function, so the stem also helps transport energy-rich food from the leaves (made during photosynthesis) and water and nutrients to the cells that need it. Transportation occurs throughout the plant through a system that works similarly to how our blood vessels carry oxygen and nutrients in our bodies. While the plant tissues that support transportation, also called vascular tissue bundles, are not obvious when looking at the stem from the outside, we can see them easily in the veins of leaves, which continue into the stem and down into the roots. The part that transports water from the roots is called the xylem. It is like a bundle of pipes running through the plant that helps strengthen the stem.

Stem Adaptations

Adaptations are changes in life forms over time that improve their potential to survive. Because of these adaptations, plants may have stems of different textures, shapes, and colors depending on their habitat. Stems can also adapt to have other capabilities, such as influencing how the plant photosynthesizes, responds to air movement, and adapts to changes in the availability of nutrients and water.

• Stems can have stout and woody textures, like the trunk of the cork oak. The spongy bark that covers the trunk protects the tree from wildfire and has been used to make cork for thousands of years. 

• Aquatic plants, like water lilies, often have soft and flexible stems with small compartments of air that help support them in water.

• Stems like grapevines can be thin and wiry in shape, which helps plants cling to higher structures so their leaves get more sunlight.

• Like leaves, stems can be green because they contain chlorophyll, the pigment that helps plants make food through photosynthesis. In dry habitats, plants that lose their leaves during long dry spells, like the palo verde tree (Parkinsonia), can still make food because they have chlorophyll in their stems. 

• Spines or thorns can cover stems, defending the plant from hungry animals. The prickly California native rose, Rosa minutifolia, is a good example of this adaptation. 

• In the case of the rattan palm (a plant commonly used to make rattan furniture), spines or thorns can also help the plant support itself by gripping other, larger plants.

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