HORTICULTURE

Detailed explanation-1: -Sieve tubes are formed by sieve elements, also referred to as sieve-tube members, arranged end to end in a chain. Sieve elements have pores called sieve plates between them. These pores allow the pass of nutrients through phloem tubes. Sieve elements are living cells at functional maturity.

Detailed explanation-2: -The companion cells are specialized parenchyma cells in the phloem tissues of the angiosperms. They are nucleated living cells with several ribosomes, plastids, and mitochondria.

Detailed explanation-3: -Companion cells function to load and unload sugars into the cavity of sieve tube members.