The plant's transportation systems

Within all plants there are two continuous systems which manage the transportation of sugars, nutrients and water around the plant. These are called the phloem and xylem systems.

Effectively these form the plumbing of the plant; tubes which extend throughout the structure of the plant, much as a human’s network of arteries and blood vessels. The midrib and veins you see on leaves are the xylem and phloem tubes.

Xylem

The xylem transport system carries water from the roots to the rest of the plant. Dissolved within the water are nutrients the plant has drawn in from the soil, so these are also transported by the xylem. If you stand a fresh stick of celery in coloured water, you will see that the water is slowly drawn up through the celery – this is by the xylem tubes (just make sure that you have the stick the right way up!).

Phloem

Sugars are produced by the process of photosynthesis which predominantly takes place in the plant’s leaves. However, these sugars are needed for energy throughout the plant, so the phloem system transports the sugars from the leaves down to the rest of the plant. On leaves the phloem tubes run along the lower surface, which is why you see aphids on the underside of the leaves (as they are sucking on the sugary phloem solution).