English: Dextridnoid reaction:

Perenniporia medulla-panis is a fungus that, consistent with the taxonomic classification, is affiliated with the division Basidiomycota, family Polyporaceae. The species is lignicolous, i.e. the mycelium occurs and develops on old, large fallen trunks and stumps, or on old living trees in the trunk cavities; in terms of ecology, it is considered a saprotrophic species. On the tree surface, the fungus forms perennial fruiting bodies attached to the substrate (resupinate) to weakly protruding, and the hymenophore consists of pores. The fruiting bodies are white when young, then slightly darker, while the pores are small and round in shape.

For this experiment, two microscopic slides with different reagents are to be prepared, one with water and one with Melzer's reagent, in order to discern the differences in the reaction, the color change of the structures. Melzer's reagent is an aqueous solution of chloral hydrate, potassium iodide, and iodine in a certain ratio. Perenniporia medulla-panis has a positive dextrinoid reaction, i.e. iodine reacts with glycine betaine and a dark-brown or reddish-brown color of the observed structures occurs. For comparison, the preparation made in water yields no reaction and the structures do not alter their color.

А fruit body is laid onto a binocular and the surface pores are clearly visible. A microscopic glass slide is prepared by placing one drop of water on one side and one drop of Melzer's reagent on the other side. By using a clean razor, very thin longitudinal parallel sections are made on the fruiting body followed by a cross-section; afterwards, the material is put into the reagents. A cover glass is laid on top and pressed with absorbent paper in an attempt to position the material in one plane and expel the air. Given that this fruiting body is very firm (both dry and fresh), it is necessary to break the material further by gently tapping the cover glass. It is evident from the slides that the one prepared in water has no staining at all while the material in the Melzer's reagent is dark-brown in color. First, the material prepared in water medium is observed by microscope, displayed at 100x magnification (10x objective lens); it is perceptible that the spores and hyphae are transparent. At higher magnification of 400x (40x objective lens), and later at 1,000x magnification (100x objective lens), elliptical to globular spores and thick-walled hyphae are observed. Afterwards, the second microscopic slide in Melzer's reagent is examined, where a dark-brown color of the hyphae is visible at 100x magnification; subsequently, at 400x magnification, the elliptical to spherical brown spores are seen, i.e. they are not transparent as in the previous preparation.

Planned and performed by Slavica Tofilovska and Katerina Rusevska, Department of Biology, FNSM, Ss. Cyril and Methodius University, Skopje, Macedonia.