stemsistä

Stems are a fundamental component of vascular plants, serving as the primary structural axis that supports leaves, flowers, and fruits. They are responsible for transporting water and nutrients from the roots to the rest of the plant, and also for translocating sugars produced during photosynthesis from the leaves to other parts of the plant. Stems exhibit a variety of forms and functions depending on the species and its environment.

The internal structure of a stem typically consists of several layers. The epidermis forms the outermost protective layer. Beneath the epidermis is the cortex, which may contain parenchyma cells for storage and collenchyma or sclerenchyma cells for support. The stele, located at the center, contains vascular tissues: xylem for water transport and phloem for sugar transport. In dicotyledonous plants, these vascular tissues are often arranged in distinct bundles, while in monocotyledonous plants, they are scattered throughout the stem.

Stems can be modified for various purposes. For instance, underground stems like rhizomes, bulbs, and tubers are adapted for storage and vegetative reproduction. Aerial stems can be modified into tendrils for climbing, spines for defense, or phylloclades which resemble leaves and perform photosynthesis. The growth of a stem in length is typically achieved through the activity of apical meristems located at the tip, while secondary growth, leading to an increase in girth, occurs in woody plants through the vascular cambium and cork cambium.