Question

Why is septum between 2 sieve tube elements called sieve plate??

Answer 1

Sieve tube cells are placed end to end in phloem. The end walls may be transverse or oblique. They have many small pores called sieve pits. Each sieve pit is lined by a layer of callose. Excessive growth of callose closes the sieve pores. Due to the presence of sieve pits the end walls are commonly called sieve plates.