Jim Bidlack - BIO 5354/4354 PLANT ANATOMY Lecture 16 - Root Systems I. True vs. adventitious roots A. True roots - gymnosperms, most dicots, some monocots (often have secondary growth) 1. Tap root: Radicle elongates and becomes a main root - can be referred to as a taproot although the root system should still be called fibrous 2. Fibrous root: arise and hang down from certain area (NOTE: all root systems are fibrous) B. Adventitious roots - most monocots, some dicots 1. Refers to roots arising not at their usual sites 2. Often occurs as repeating patterns on ground-level stems (stolens) or roots (rhizomes) C. Why adventitious root systems? 1. Water pipe analogy - Plants without secondary growth need more water pressure to get enough water into the plant. They do this by forming numerous water "inlets" as part of the adventitious roots system. 2. Even with adventitious roots, monocots are still restricted in size II. Other facts about roots A. Most roots do NOT grow down - the majority are horizontal roots arising from vertical roots
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