It is the food conducting channel in plants and is made up of 4 components:
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Sieve tube elements which are living cells placed end to end to form the elongated conducting channel, sieve tube. Sieve tube cells lack nucleus and have perforated end walls that form the sieve plate.
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Companion cells those are associated with sieve tubes through compound plasmodesmata between them. Companion cells are parenchymatous with large nucleus and dense cytoplasm.
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Phloem parenchyma are living elongated parenchyma cells with thin cellulosic walls and tapering ends. The wall of phloem parenchyma cells has pits for plasmodesmatal communication with other cells.
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Phloem fibres (bast fibres) are sclerenchymatous cells forming elongated, unbranched fibres with needle like apices.
