Which of the following statements is true for phloem in plants ?
The companion cells are specialised parenchymatous cells, which are closely associated with sieve tube elements. The sieve tube elements and companion cells are connected by pit fields present between their common longitudinal walls. The companion cells help in maintaining the pressure gradient in the sieve tubes.
A mature sieve element possesses a peripheral cytoplasm and a large vacuole but lacks a nucleus. Sieve tube elements are also long, tube-like structures, arranged longitudinally and are associated with the companion cells. Their end walls are perforated in a sieve-like manner to form the sieve plates.
Phloem parenchyma is made up of elongated, tapering cylindrical cells which have dense cytoplasm and nucleus. Phloem parenchyma is absent in most of the monocotyledons.
Phloem fibres (bast fibres) are made up of sclerenchymatous cells.
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