3: Roots
Roots are plant organs that are usually found underground. They not only anchor the plant, but also transport water, minerals, and sugars. In many plants, carbohydrates are stored in the roots so they can be used when needed. Roots can be very deep, and spread out very far. Some roots are as deep as the tree is high. Roots can also spread far beyond the canopy of the tree. However, being underground, they are often gone unnoticed.
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- 3.2: External Root Structure
- Taproots and fibrous roots are the two main types of root systems. In a taproot system, a main root grows vertically downward with a few lateral roots. Fibrous root systems arise at the base of the stem, where a cluster of roots forms a dense network that is shallower than a taproot.
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- 3.3: Internal Root Structure
- The growing root tip is protected by a root cap. The root tip has three main zones. The root's ground tissue contains cortex and pith while its vascular tissue contains xylem and phloem. Monocots and dicot have different organization of their vascular tissues. Many roots have secondary growth as well as primary growth. Secondary growth occurs by the production of two types of meristemic tissue, the vascular cambium and the cork cambium.
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- 3.4: Root Modifications
- In some habitats, the roots of certain plants may be modified and adapted for various environments. Some examples of these modifications result in storage roots, aerial roots, epiphytic roots, contractile roots, stilt roots, penumatophores, and photosynthetic roots. Root nodules and mycorrhizae are root adaptations that increase the efficiency of nutrient uptake.
Attribution
Kammy Algiers ( CC BY-NC )
Thumbnail: Carnegie Institution of Washington (1919) from Wikimedia Commons , No restrictions