Cambium and pith are two distinct plant tissues that play fundamentally different roles in a plant's structure and growth. While pith is a central storage tissue, typically found in the primary growth phase, cambium is a lateral meristematic tissue responsible for secondary growth, which increases the plant's girth.
Here's a breakdown of their key differences:
| Feature | Cambium | Pith |
|---|---|---|
| Location | Between xylem and phloem (vascular cambium), or between cortical tissues and epidermis (cork cambium) | Center of the stem or root |
| Function | Produces new xylem and phloem (secondary growth), or forms bark (cork cambium) | Storage of water, starch, and nutrients |
| Tissue Type | Meristematic (actively dividing cells) | Ground tissue (primarily parenchyma cells) |
| Role in Growth | Increases stem/root diameter (girth) | Primary growth support; often diminishes in older stems |
| Cell Activity | Cells continually divide and differentiate | Cells are largely differentiated and inactive in division |
Detailed Comparison of Cambium and Pith
Understanding the specific roles and locations of cambium and pith provides insight into the complex architecture of plants.
Location and Structure
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Pith: The pith is centrally located within the stem and roots of vascular plants. It forms the innermost tissue, surrounded by successive concentric layers of sap-conducting tissues, specifically the xylem and phloem. Composed primarily of soft, spongy parenchyma cells, the pith often appears as a distinct core. In many older stems, the pith may be crushed, become hollow, or fill with air as secondary growth progresses.
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Cambium: The term "cambium" refers to layers of undifferentiated meristematic cells that facilitate growth. There are two primary types:
- Vascular Cambium: This critical layer is situated between the primary xylem and primary phloem within the vascular bundles. It's responsible for producing secondary xylem (which forms wood) towards the inside and secondary phloem towards the outside.
- Cork Cambium (Phellogen): This cambium develops later in the outer cortical regions and is found between the cortical tissues and the epidermis. Its function is to produce cork cells (phellem) outwards and phelloderm inwards, forming the protective outer bark of woody stems and roots.
Function and Role in Growth
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Pith: The primary function of the pith is the storage of nutrients, such as starch and water. In young stems, it can also provide some structural support. As a plant grows older and undergoes secondary thickening, the pith's role diminishes, often becoming less prominent or even disintegrating in woody plants. Its cells are part of the plant's ground tissue system.
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Cambium: The cambium is crucial for the secondary growth of plants, which leads to an increase in their diameter.
- The vascular cambium actively divides to produce new vascular tissues. This process is responsible for the formation of annual growth rings in trees, as it generates the wood we use. Without vascular cambium, trees and other woody plants would not be able to increase in girth or produce durable wood.
- The cork cambium protects the plant from water loss, pathogens, and physical damage by forming the periderm, which replaces the epidermis in older stems and roots.
Practical Insights
- Wood Production: The activity of the vascular cambium is directly responsible for all the wood produced by trees. Each year, a new layer of secondary xylem is added, creating the visible growth rings used to determine a tree's age and past environmental conditions.
- Plant Structure: In young herbaceous plants, the pith is often prominent and contributes significantly to the stem's initial structure. As these plants mature or as woody plants age, the active growth of the cambium leads to the development of a strong, thick stem, often reducing the relative size or even the presence of the pith.
In essence, while the pith is a static storage component from the plant's primary growth, the cambium is a dynamic growth engine driving the plant's expansion in width and forming its protective outer layers.
