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Questions and Answers
What is the function of grafting?
What is the function of grafting?
To artificially unite stems or parts of stems of different but related varieties of plants.
What are the types of leaf arrangements on a stem?
What are the types of leaf arrangements on a stem?
What does the axil refer to in plant anatomy?
What does the axil refer to in plant anatomy?
The angle between the petiole and the stem.
Deciduous trees lose all their leaves annually.
Deciduous trees lose all their leaves annually.
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The ________ produces primary xylem and phloem.
The ________ produces primary xylem and phloem.
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What do leaf primordia develop into?
What do leaf primordia develop into?
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What type of stele is characterized by a solid core with phloem surrounding xylem?
What type of stele is characterized by a solid core with phloem surrounding xylem?
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What is the role of cork cambium in plants?
What is the role of cork cambium in plants?
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Study Notes
Introduction to Stems
- Stems are a primary source of wood in household items.
- Grafting is a technique used to unite different plant varieties.
- Some plants exhibit indeterminate growth, allowing them to continue growing indefinitely.
External Form of a Woody Twig
- Woody twigs consist of an axis with attached leaves, defined by nodes and internodes.
- Node: Location where leaves attach; can be alternate, opposite, or whorled.
- Internode: Region between nodes on the twig.
- Leaves consist of a flattened blade attached to a twig via a petiole.
Anatomy of a Woody Twig
- Axil: Angle formed between the petiole and stem, containing an axillary bud, which can develop into branches or flowers.
- Terminal Bud: Located at the twig tip, promotes elongation of the twig.
- Bud scales protect developing buds, while stipules are leaf-like appendages at the base of leaves.
Deciduous Trees and Shrubs
- Deciduous varieties shed all leaves annually, leaving dormant axillary buds with leaf scars.
- Bundle scars within leaf scars indicate presence of food and water-conducting tissues.
Origin and Development of Stems
- The stem tip contains apical meristem, which contributes to lengthening and is dormant until the growing season.
- Leaf primordia are tiny embryonic leaves that develop into mature leaves, protected by bud scales.
Primary Meristems
- Apical meristem produces three primary meristems:
- Protoderm: Forms the epidermis.
- Procambium: Gives rise to primary xylem and phloem.
- Ground Meristem: Produces pith and cortex (comprised mainly of parenchyma cells).
Leaf and Bud Primordia
- Leaf and bud primordia derive from the primary meristem and contain traces of xylem and phloem that connect to leaves and buds.
Vascular Cambium
- A layer between primary xylem and phloem can differentiate into vascular cambium.
- Cells from the vascular cambium form secondary xylem (wood) inward and secondary phloem outward.
Cork Cambium
- Cork cambium produces cork cells containing suberin (for waterproofing) and phelloderm cells.
- Functions to reduce water loss and protect the stem; lenticels facilitate gas exchange.
Tissue Patterns in Stems (Steles)
- Stele: The central cylinder comprising primary xylem, phloem, and possibly pith.
- Types of steles:
- Protostele: Solid core with phloem surrounding xylem; found in primitive seed plants.
- Siphonosteles: Tubular with pith, common in ferns.
- Eusteles: Composed of discrete vascular bundles; typical in flowering plants and conifers.
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Description
Explore the fascinating world of plant stems in Chapter 6. This chapter covers the introduction to stems, their external forms, and the origin and development of various types, including woody and herbaceous forms. Discover essential tissue patterns and structures unique to stems.
