PPM, isn't that concentration abbrev. for parts per million? If you can reduce contamination to less than parts per million, then your kitchen hood would be sterile enough for tissue culture. But anyway, it is Plant Preservative Mixture biocide, just don't know what kind
I like the way you think Joe, that's what I thought too, "Parts per Million". But apparently it stands for "Plant preservative material". Some smart guy has invented it and now sells it at a blood-price. They say it's crucial for avoiding contamination.
Thanks for info on meristems.