garden of scallions

Sunday I dared a grocery run and came back with 5 bunch of scallions in my haul. I cut up 3 to freeze, leaving some green above the roots, then put all five in glasses of water. I think they''ve grown an inch or so since. The cut bunches are pretty obvious: I had cut them cleanly with scissors, but now there's new growth coming from inside the stalks, like a pipe within a pipe. The other two bunches are less clear, no sleeve action like that, but some stalks are longer than others despite my cutting for fresh scallion use. It's possible I missed some though.

CO2 and H20 have obvious sources, but where are the minerals for new growth coming from? I assume mostly cannibalizing the roots, but Los Angeles water is pretty 'hard'. Hmm, there's an idea for a science experiment, compare growth in tap vs. distilled water...