Root System

The root is the non-green, cylindrical, descending axis of the plant that develops from the radicle - the first structure to emerge when a seed germinates in soil - and normally grows downward into the ground (it is positively geotropic and negatively phototropic). Roots absorb water and dissolved minerals from the soil and anchor the plant firmly. Characteristically, roots lack nodes, internodes and buds (sweet potato and members of the Rutaceae are exceptions, where roots do bear buds used in vegetative propagation), are usually non-green because they lack chlorophyll, and bear root hairs that increase the absorptive surface for water and minerals. The growing root tip is protected by a dome-shaped root cap (Pandanus has multiple root caps; Pistia has a root pocket instead of a cap). Just behind the cap, the root is organised into three zones by meristematic activity: the meristematic zone (region of cell division), lying just above the cap, where cells actively and continuously divide and is the main growing point; the zone of elongation, just above it, where the newly divided cells lengthen and drive the increase in roo …