Mass flow in the phloem- part 1
Active transport actively loads solutes into the phloem into sieve tubes.
Lowers water potential inside phloem
High pressure at source end of sieve tubes.
Mass flow part 2
Sink end solutes are removed to be used up.
Increases water potential inside sieve tubes- water leaves by osmosis.
Lowers pressure inside sieve tubes.
Pressure gradient from source to sink end
Pushes solutes to where they're needed