Editing Phloem (section)

===Conducting cells (sieve elements)===
[[File:Phloem and Xylem in stem.svg|thumb|Simplified phloem and companion cells: {{ordered list |[[Xylem]] |Phloem |[[Cambium]] |[[Pith]]|Companion cells}}]]

[[Sieve tube element]]s are the type of cell that are responsible for transporting sugars throughout the plant.<ref name="Raven et al. 1992" /> At maturity they lack a [[Cell nucleus|nucleus]] and have very few [[organelle]]s, so they rely on companion cells or albuminous cells for most of their metabolic needs. Sieve tube cells do contain [[vacuole]]s and other organelles, such as [[ribosome]]s, before they mature, but these generally migrate to the cell wall and dissolve at maturity; this ensures there is little to impede the movement of fluids. One of the few organelles they do contain at maturity is the rough [[endoplasmic reticulum]], which can be found at the plasma membrane, often nearby the [[plasmodesmata]] that connect them to their companion or albuminous cells. All sieve cells have groups of pores at their ends that grow from modified and enlarged plasmodesmata, called ''sieve areas''. The pores are reinforced by platelets of a [[polysaccharide]] called [[callose]].<ref name="Raven et al. 1992" />