In phloem tissue, long, narrow food-conducting cells are arranged end to end in ranks. Their end walls (called sieve plates) are pierced with holes, a characteristic giving columns of these cells the name sieve tubes. Threads of living cytoplasm pass from cell to cell through the sieve plates. An interesting feature of sieve tube members is that they lack nuclei, leaving their cytoplasm free to transport food. Sustaining the living cytoplasm of these cells is the work of nuclei located in adjacent companion cells.
