external plant parts
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Types of stems
Stems may be long, with great distances between the leaves and buds (e.g., branches of trees, runners on strawberries) or compressed, with short distances between buds or leaves (e.g., crowns of strawberry plants, fruit spurs, and African violets). Although stems commonly grow above ground, they sometimes grow below ground in the form of rhizomes, tubers, corms, or bulbs. All stems must have buds or leaves to be classified as stem tissue.
Specialized aboveground stems
Some plants have specialized aboveground stems known as crowns, spurs, or stolons (Figure 7). Crowns (on strawberries, dandelions, and African violets) are compressed stems with leaves and flowers on short internodes. Spurs are short, stubby, side stems that arise from a main stem. They are the fruit-bearing stems on pear, apple, and cherry trees. If severe pruning is done close to fruit-bearing spurs, they can revert to nonfruiting stems, thus eliminating the year's potential fruit crop.
Figure 7. Diversified aboveground stem development.
Stolons are fleshy or semiwoody, elongated, horizontal stems that often lie along the soil surface. Strawberry runners are stolons that have small leaves at the nodes. Roots develop from these nodes, and a daughter plant is formed. This type of vegetative reproduction is an easy way to increase the size of a strawberry patch. Spider plants also produce stolons, which ultimately can become entirely new plants.
