A One-Solution Tannic-Aced-Iron Stain for Plant Tissue Sections

After completing the bulletin on “Actinomycetes in various parts of the potato and other plants” (Lutman, 1945) the author found the beautiful plates in the atlas to Olivier's monograph (1881) on root structure in which the same intercellular inclusions were shown. Olivier stated that he had stained his sections in “tannate of iron”. Attempts were made by the author to prepare and use such a combination but they were unsuccessful owing to the precipitate that was formed.

The formula used by the U. S. government for ink for official use was tried. This combination is composed of tannic and gallic acids with ferrous sulphate and is acidified with hydrochloric acid. When used double strength, as suggested for special blackness and permanence, the stain was very successful on sections of potato roots and tubers. It stained the Actinomyces hyphae very differentially and was decolorized from all other cell organs. Any other stains used dyed also the pectins and the Actinomyces secretions (melanins) but with this iron tannate combination in one solution, the finest hyphae could be seen and photographed. Since hydrochloric acid was used in this stain, such Actinomyces inclusions must be very tannophylic; much more so than any animal intercellular inclusions so far described.