Roots

Roots serve two important functions - the first is purely mechanical, as they are responsible for anchoring the plant firmly within the ground. In epiphytes, the roots also serve to anchor the plant to others. The second important function is ensuring that an adequate supply of water and nutrient reaches the aerial parts of the plant, via the xylem. The roots also contain phloem tissue which is the pathway through which assimilated carbohydrate moves from the points of synthesis (source) to the sites of storage (sinks).

The detail of an Iris root shown in cross section to the left contains a very prominent  endodermis. The endodermis cells are lignified, and have conspicuously thickened radial and inner tangential walls. Note the two thin-walled passage cells, which, as their name implies, allows the passage of water and nutrient from the cortex (above) to the xylem within the stele. Passage cells are also the route taken by carbohydrate to the living cells within the cortex, from the stele.

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