Other specified procedures are more complicated and time consuming
because they include keeping the pollen in stain for 24–48 h on
50 ◦C or even fixation prior to staining. The acetic acid quantity
also changed (influencing pH) in relation to the pollen type. Green
color of non viable and red color of viable pollen grain is obtained
because the cell wall is always stained with malachite green (non
viable pollen grain is empty) while protoplast is stained with acid
fuchsin.