Dyeing the cross-sections for lignin

Dyeing the cross-sections

2 - Phloroglucinol/HCl is used to dye lignified cell walls red
Phloroglucinol/HCl (figure 2) is used to dye lignified cell walls red. This dye works best for herb-chronology because it pronounces the structures you are interested in (the vessels and lignified parenchyma that often adds to the visualization of growth rings in the roots). To prepare the dye dissolve 1-2 points of a spattle of the phenol derivative phloroglucinol (also known as phloroglucin) in 20 ml of 75% alcohol. Use HCl conc. (≥32%) as the other reagent. Using dropper bottles you first apply one drop of phloroglucinol/EtOH to the cutting and, after 5-10 seconds or so, add one drop of HCl. In most cases this produces instantaneous reddish colouring of the lignified tissue. For thin cuttings where only the vessels are lignified colouring may take a little while. In this case do not take the photographs too quickly or you might end up with photos of low contrast. To help speed up colouring you might add a second drop of HCl. On the other hand, thicker cuttings or those that have a lignified parenchyma may colour quickly and deeply so that you should take the photo quickly to prevent dark photographs. In this case you should reduce the amounts of dye applied to the cuttings. If you do not produce satisfactory colouring try to add some more phloroglucinol to the alcoholic solution.