I use these to presprout garden seeds in a sterile environment. I place a folded paper napkin or paper towel into the petri with a coffee filter cut out to form a shallow "dish" on top. I soak the paper with a splash of boiling water to sterilize, then allow to cool. The seeds are then spaced in this filter paper dish which prevents the sprouts from rooting into the moist paper napkin. The sprouts are then planted into cell flats for 100% germination in the flats.