HERVE CONGE, ISM / SCIENCE PHOTO LIBRARY HERVE CONGE, ISM / SCIENCE PHOTO LIBRARY
Grape vine stem showing sieve tube cells in its phloem, light micrograph. Phloem is the tissue responsible for transporting sugars and other nutrients around the plant. It comprises tubular cells with sieve plates between them. These are supported by companion cells. The sieve plates, as their name implies, are perforated with numerous holes. One sieve plate is seen at centre as a row of dots. The solution in phloem can move in either direction, depending on where in the plant the nutrients are required. This is in contrast to xylem tissue, which can only move water upwards from the roots to the leaves. Magnification: x110 when printed 10cm wide.
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