- Flowering plants (angiosperms) are subdivided into two groups, monocots and dicots, based on how the embryo develops and whether the seed has one or two cotyledons (or "seed leaves"). Plants with one cotyledon are monocots, and plants with two are dicots.
- Vascular bundles are the tubular transport system in flowering plants. They are differentiated into the xylem and phloem, depending upon whether they transport water and nutrients from the roots to the upper plant (xylem) or whether they transport carbohydrates and sugars from the leaves to the rest of the plant (phloem).
- In monocots, which includes mostly herbaceous plants, such as grasses, lilies, and orchids, the xylem and phloem bundles are scattered throughout the stem of the plant.
- By contrast, vascular bundles in dicots occur in distinct rings within the stems of the plants. If you make a cross section of the stem, these vascular bundles form a cylinder that resembles a ring of spots within the stem of the plant.
- If the dicotyledon plant is a woody perennial (in other words, a tree), then growth rings will form and be visible at the outside edge of the cross section. In fact, each year's growth will leave a permanent circle in the old growth part of the stem or trunk. Only in the center of the stem (or trunk) are the vascular bundles still alive.
- Woody monocots grow year after year without leaving a distinctive growth ring. Palms are a familiar woody monocot. Other examples include agave and yucca plants.
