It evolved as a response to the increase in the size of plants, which caused an progressing separation of roots and leaves in space. Thus, plants developed systems for long distance transport - that is, translocation. In that way became the exchange of the products of absorption and assimilation possible. The system consists of xylem and phloem. The xylem is the tissue that translocates water and minerals.
Transport occurs acripetally, i.e. in the direction of the shoot's tip.
The phloem is the tissue that translocates assimilates from mature leaves to growing or storage organs and roots. The xylem transports water and dissolved ions. The main portion of the water is taken up by young roots. Absorption occurs directly by the rhizodermis , and the area that takes up water and ions is enlarged by the formation of root hairs . From there flows the water through the cortex that may be developed as an exodermis, through the endodermis, the innermost layer of cortical cells and into the cells of the stele's vascular bundles.