 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.