Xylem and phloem are the two conducting tissues of a vascular plants. They are referred to as vascular bundles. Xylem and phloem are responsible for conducting certain substances from one part of the plant to another.
The xylem is responsible for conducting WATER AND DISSOLVED MINERALS from the root of the plants to other parts e.g leaves, stem, flowers etc. while the phloem conducts sugar (product of photosynthesis) e.g glucose from the leaves of the plant to other parts including the stem, root etc.
According to this question, xylem or phloem does not conduct or carry gaseous substances like carbon dioxide (CO2).
