1. Vascular Tissue:
* Xylem: These cells transport water and dissolved minerals from the roots to the rest of the plant.
* Tracheids: Long, narrow cells with thickened cell walls and pits for water transport.
* Vessel Elements: Shorter, wider cells with perforated end walls, forming continuous tubes for efficient water flow.
* Phloem: These cells transport sugars and other organic compounds produced during photosynthesis from leaves to the rest of the plant.
* Sieve Tube Elements: Long, thin cells with perforated sieve plates at their ends, allowing for the movement of phloem sap.
* Companion Cells: Smaller cells that support and regulate the activity of sieve tube elements.
2. Ground Tissue:
* Parenchyma: These are the most abundant cells in the stem, filling spaces between vascular bundles. They store food, water, and other substances, participate in photosynthesis, and contribute to structural support.
* Collenchyma: These cells have thickened cell walls, providing flexible support and strength to the stem, particularly during growth.
* Sclerenchyma: These cells have extremely thick, rigid cell walls and are often dead at maturity. They provide structural support and strength to the stem.
* Fibers: Long, narrow cells, typically found in bundles, offering tensile strength.
* Sclereids: Short, irregularly shaped cells, often found in seed coats and fruit, contributing to hardness.
3. Dermal Tissue:
* Epidermis: This outermost layer of cells protects the stem from damage and water loss. It can have specialized structures like stomata for gas exchange and trichomes for defense.
* Periderm: In older stems, the epidermis is replaced by the periderm, a protective layer consisting of cork cells, cork cambium, and phelloderm.
4. Other Cells:
* Meristematic Cells: These are undifferentiated cells found in specific regions of the stem, responsible for growth and development.
* Apical Meristem: Located at the tip of the stem, responsible for primary growth, increasing stem length.
* Lateral Meristem: Found in the vascular cambium (producing vascular tissue) and cork cambium (producing periderm), responsible for secondary growth, increasing stem girth.
The specific types and arrangement of cells in a stem vary depending on the plant species, age, and environmental conditions.
