The phloem constitutes of the following four elements:
1 . Sieve tubes
The main functions of sieve tube members is to maintain the cells and transport the necessary molecules with the help of companion cells. The sieve tube members are living cells but they do not contain a nucleus.
2 . Companion cells
It functions in phloem loading and unloading, long-distance transport, and as a quality control center for monitoring the nature of substances passing into and out of the phloem.
3 . Phloem parenchyma
Phloem parenchyma cells, also called as transfer cells and border parenchyma cells, are located near the finest branches and terminations of sieve tubes in leaf veinlets, where they help in the transport of food materials.
4 . Phloem fibres
The phloem fiber is narrow and elongated. It occurs both in the primary phloem and the secondary phloem.