Plants Anatomy

The body of a vascular plant is organized into three general kinds of organs: roots, stems, and leaves.

Roots basically anchor the plant to its substrate and absorb water and minerals. Unlike stems, they have no leaves or nodes. The epidermis (outer layer) is just behind the growing tip of roots and is covered with root hairs, which are outgrowths of the epidermal cells. The root hairs increase the surface area of the roots and serve as the surface through which water and nutrients are absorbed.

Inside a root consists largely of xylem and phloem. Some roots are important food and storage organs. Many tropical trees, such as those found on Ista, have aerial prop roots that serve to hold the stem in an upright position. Roots increase in length through the activity of apical meristems and in diameter through the activity of lateral meristems.

Stems usually are above ground, grow upward, and have leaves, which are attached in a regular pattern at nodes along the stem. The portions of the stem between nodes are called internodes. Stems increase in length through the activity of an apical meristem at the stem tip. This growing point is where new leaves form and surrounds and protects the stem tip, or apical bud, before they expand.

Stems also consist of the three tissue systems and have several features in common. Vascular tissue is present in bundles that run the length of the stem, forming a continuous network with the vascular tissue in the leaves and the roots. Stems increase in diameter through the activity of lateral meristems, which produce the bark and wood in woody plants. The bark, which also contains the phloem, serves as a protective outer covering, preventing damage and water loss.

The leaf is the primary photosynthetic organ of most plants. Leaves are usually flattened blades that contain mainly parenchyma tissue called the mesophyll, which is made up of loosely arranged cells with spaces between them. The mesophyll is bounded by the upper and lower surface of the leaf blade, which is covered by epidermal tissue.

The leaf blade is connected to the stem through a narrowed portion called the petiole, or stalk, which consists mostly of vascular tissue. Appendages called stipules are often present at the base of the petiole.

Many specialized forms of leaves occur. Some are modified as spines, which help protect plants from predators. Some leaves are brightly colored and petal-like, serving to attract pollinators to otherwise small, unattractive flowers. Perhaps the most highly modified leaves are flowers themselves. The individual parts of flowerscarpels, stamens, petals, and sepalsare all modified leaves that have taken on reproductive functions.

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