Companion cells provide the energy for the sieve cells. The end walls of the sieve cells have pores through which sugar is transported from cell to cell.
8. In carbohydrate-high tomato plants the reduction of nitrates was localized in the following regions: at the stem tip just behind the growing region; in the leaf cells, especially near the phloem ...
In a mature flowering plant or tree, most of the cells that make up the xylem are specialised cells called vessels.