Sugar made in a leaf is needed elsewhere in the plant. What does that tell you about transport in phloem?

Erklärung

The parts that use or store sugar sit both above and below the leaf that made it, so the delivering tissue has to be able to run either way along the stem. A downwards only rule would leave a growing shoot tip and a ripening fruit with no supply at all, and both of them plainly receive sugar while they develop.