The conducting cells of phloem are called sieve elements. Sieve elements lack a nucleus (it disintegrates after division) but have otherwise intact protoplasts at maturity. They also have thin areas along their cell walls that are perforated by sieve pores. Solutes move from sieve element to sieve element through these pores. Sieve plates produce thin, primary cell walls and are the most delicate cells in the plant, usually living less than a year.