has a larger number of ribosomes and mitochondria. The dense cytoplasm of a companion cell is connected to the sieve-tube element by plasmodesmata. The common sidewall shared by a sieve tube element and a companion cell has large numbers of plasmodesmata.

There are three types of companion cells.
# Ordinary companion cells, which have smooth walls and few or no plasmodesmatal connections to cells other than the sieve tube.
# Transfer cells, which have