Sieve tube element

Phloem contains sieve tube elements arranged end to end. Unlike mature xylem vessel elements, they remain alive. Their end walls are not completely removed: they become sieve plates, containing many pores through which dissolved sugars and amino acids can pass from one element to the next.

Phloem is living tissue. Its conducting cells, called sieve tube elements, join end to end. Their perforated end walls let dissolved substances pass between cells, and they lack nuclei, leaving more room for transport.