What is the name of the substance moving into the roots?

Answer 1

This is a bit of a general question & I don't know the context, so it may be a far too simple answer - but it is water (with dissolved nutrients) that is usually taken up by the roots of plants!

Answer 2

Water and minerals move into the roots through a process called osmosis. These substances are absorbed from the soil by the root hairs and travel through the root tissues to reach the rest of the plant.