Functions and Terminology of Plant Stems
– Support leaves, flowers, and fruits
– Transport fluids between roots and shoots in xylem and phloem
– Store nutrients
– Produce new living tissue
– Conduct photosynthesis
– Halm or haulm or culms
– Nodes and internodes
– Axillary buds and branches
– Adventitious roots and tendrils
– Shoots vs stems
Specialized Stem Types
– Acaulescent: Stemless appearance
– Arborescent: Tree with woody stems
– Bulb: Underground stem with fleshy storage leaves
– Cladode: Flattened stem specialized for photosynthesis
– Rhizome: Horizontal underground stem for reproduction and storage
Stem Structures
– Dermal tissue: Waterproof, protect, control gas exchange
– Ground tissue: Parenchyma cells, sometimes photosynthetic
– Vascular tissue: Long-distance transport and structural support
Stem Anatomy and Function
– Stems produce secondary xylem and secondary phloem
– Cortex and epidermis are eventually destroyed
– Cork cambium develops before cortex destruction
– Periderm, consisting of cork and phelloderm, replaces epidermis
– Lenticels are areas of loosely packed cells for gas exchange
Stem Types in Different Plant Groups
– Dicot Stems:
– Pith in the center, vascular bundles in a distinct ring
– Epidermis with cuticle and stomata
– Cortex with hypodermis and endodermis
– Secondary growth from vascular cambium and cork cambium
– Formation of continuous cylinder in vascular bundles
– Monocot Stems:
– Vascular bundles are present throughout the stem
– Shoot apex is elongated and protected by leaf sheathes
– Monocots rarely produce secondary growth
– Palms and bamboo are exceptions to woody monocots
– Some monocots increase in diameter via anomalous secondary growth
– Gymnosperm Stems:
– Gymnosperms are woody plants
– Stems are similar in structure to woody dicots
– Gymnosperms produce tracheids in xylem, not vessels
– Gymnosperm wood often contains resin ducts
– Softwoods, such as pine and spruce, are gymnosperms
– Fern Stems:
– Most ferns have rhizomes with no vertical stem
– Tree ferns have vertical stems up to 20 meters tall
– Fern stems have leaf gaps in cross section
– Vascular tissue does not form a complete cylinder at leaf gaps
– Fern stems may have solenosteles or dictyosteles
Economic Importance of Stems
– Stems provide staple crops like potato and taro
– Sugarcane stems are a major source of sugar
– Wood has numerous uses in construction, furniture, and more
– Bamboo stems have hundreds of uses, including paper and furniture
– Stems of plants like flax and hemp provide fibers for textiles
