Lacto-propionic-orcein is used in the form of a 1% solution, which is prepared as follows: add 2 g orcein to 100 mL of equal parts of lactic acid and propionic acid, filter, and dilute with distilled water to make a 45% solution. Fixed material is transferred for several minutes to the staining solution; followed by squash preparation. Lacto-propionic-orcein is a very effective stain and is recommended for materials that give unsatisfactory results after either acetocarmine or aceto-orcein staining.
Drain off the fixative and place the roots in 1% acetocarmine for 1 to 3 h. Heat until the acetocarmine begins to boil. Cut off the root cap with a razor blade and squeeze the meristematic tissue out with a lancet needle. Add a drop of acetocarmine or 45% acetic acid. Place a razor blade (double-edged) to one side and add a cover slip. Tap the cover slip gently with the needle end of a probe. Slide the razor blade out and heat to a point just below boiling (steam will form beneath the slide). Then, quickly squash with thumb or forefinger between two layers of filter paper. Be careful to not move the cover slip at this point.