3.3.5: Chapter Summary

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Melissa Ha, Maria Morrow, & Kammy Algiers
Yuba College, College of the Redwoods, & Ventura College via ASCCC Open Educational Resources Initiative

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The stem of a plant bears leaves, flowers, and fruits. Stems are characterized by the presence of nodes (the points of attachment for leaves or branches) and internodes (regions between nodes).

All three tissue systems can be found in stems. In the primary stem, dermal tissue is represented by the epidermis, the outer covering of the plant. The cortex and pith (if present) represent ground tissue, and vascular tissue is found in the vascular cylinder or vascular bundles. Vascular tissue may be arranged in a continuous ring (silenostele), in vascular bundles forming a ring (eustele), or in scattered vascular bundles (ataktostele).

Primary growth occurs at the tips of roots and shoots, causing an increase in length. Woody plants may also exhibit secondary growth, or increase in thickness. Secondary meristems (lateral meristems) are responsible for secondary growth. The vascular cambium produces secondary phloem externally and secondary xylem internally, and the cork cambium produces cork externally and phelloderm internally. The cork, cork cambium, and phelloderm form the periderm, the secondary dermal tissue. Bark consists of all the tissue layers external to the vascular cambium, and wood consists of secondary xylem. Annual rings in wood reflect differences in growth due to changing water availability throughout the year.

Some plant species have modified stems or modified shoots that help to propagate new plants, store food, or deter herbivores. Examples of such modifications are rhizomes, stolons, tubers, corms, bulbs, tendrils, and thorns.

After completing this chapter, you should be able to...

Identify the main external structures of the shoot system, including the nodes, internodes, leaves, axillary buds, and axillary shoots.
Identify the structures representing each of the three tissue systems in stems.
Compare the structure of silenosteles, eusteles, and ataktosteles.
Explain the arrangement of leaf traces, leaf trace gaps, branch traces, and branch trace gaps.
Compare the origin and function of the vascular cambium and cork cambium.
Define bark and distinguish between inner and outer bark.
Explain the production of wood and relate this to annual rings.
Distinguish between heartwood and sapwood.
Distinguish between softwood and hardwood.
Identify the external features of winter twigs.
Define and provide examples of the major stem and shoot modifications.

Attribution

Curated and authored by Melissa Ha using 30.2 Stems from Biology 2e by OpenStax (licensed CC-BY)