Why don’t dissolved organic matter moving from leaves to roots mix with water that flows from roots to leaves?

The conductive tissue of plants forms two streams: ascending (the movement of water with minerals from the root to the leaves) and descending (the movement of solutions of organic substances from the leaves to the roots). These two streams do not mix because they are formed by different types of conductive tissue, which are located in different layers in the stem:
– ascending stream – xylem (dead cells, vessels) in the wood of the stem;
– downdraft – phloem (living cells, sieve tubes) in the bark layer – bast.