"companion cell." YourDictionary, n.d. Web. 14 July 2019. <https://www.yourdictionary.com/companion-cell>.
companion cell. (n.d.). Retrieved July 14th, 2019, from https://www.yourdictionary.com/companion-cell
A specialized parenchyma cell, located in the phloem of flowering plants and closely associated with the development and function of a sieve-tube element. Companion cells probably provide ATP, proteins, and other substances to the sieve-tube elements, whose cytoplasm lacks many structures necessary for cell maintenance.