We have looked at seeds and roots of plants, and now we are going to study the stems.

Plant stems are defined as the axis, or the center portion of the plant, connecting the roots to the branches, leaves and flowers. Stems are comprised of plant cell tissue called cellulose, as a wall surrounds each plant cell.

The cellulose builds the plant’s structure, much like bones in us. As the plant wilts, it keeps its body, but the loss of water causes the plant cells to shrink.

The stem is the transpiration system, carrying water and minerals up from the roots to all the upper regions, called xylem.

This vascular system (think the “strings” in a stalk of celery) travels one way — up.

Phloem, the other vascular system, travels both up and down the plant, transporting the synthesized food (sugars) from the leaves throughout the plant. The stem also is a storage site for food and water, as well as storage in tubers, rhizomes and corms.

As well, the green in the stems is a site of active photosynthesis.

The tissue of plants can also differ by the type of plant. Annuals have just one season of growth, development, completion of its lifecycle and then death.

On the other side of the leaf, biennials have one season of vegetative growth, then the second season it completes its lifecycle, then dies. A perennial produces for many years, with woody stems outside and living growing tissue on the inside of the stem.

There are various modifications and adaptations of stems. Above ground, these include tendrils, thorns, rootlets, twining stems, stolons (runners), heads and rosettes. Underground, stems can form as bulbs, tubers, rhizomes or corms.

The stem responds to the Earth’s gravity as well. It grows upwards away from the center of the earth (called negative geotropism).

The roots grow toward the center of the earth (called positive geotropism). Other tropisms are phototropism, where plants grow toward the light; hydrotropism, where they grow toward the moisture in the soil; and lastly, some plants manifest thigmotropism, where plants respond to touch.

The stem adapts growths called tendrils that move and search to find something to wrap around. This anchors growth, so the plant does not fall. Grapes, wisteria, clematis and morning glories are great examples of stem adaptation for plant success.

Hughes is an Ohio State University Extension Master Gardener Volunteer in Mahoning County.