Talk about the companion cells of phloem

Specialized elongated parenchymatous cells, retain both their nuclei and their cytoplasm at maturity. They are closely associated with sieve tubes communicating through numerous plasmodesmata. Their nucleus controls both their own and the cytoplasm of the adjoining sieve elements after the latter nucleus is disintegrated. The function of a sieve cell lasts for a short time, when they die companion cells divide longitudinally to give two cells one of which replaces the dead sieve cell and the other gives the companion cell.