The Effects of Various Reagents, Mounting Media, and Dyes on the Teliospore Walls of Tilletia Contraversa Kühn

Owing to their composition, the teliospore walls of the smut fungi require hydrous mounting media for microscopic observations. Tilletia contraversa Kühn possesses a mucilaginous sheath. It is differentially sensitive to the dehydrating tendencies and to the chemical nature of diverse reagents used in formulating various mounting media. Some reagents are astringent, and others over-expand structures. The sheath tends to over-expand under alkaline conditions and to contract variably under acid conditions. The reticulum, on the other hand, is not greatly affected by pH. Both the sheath and the reticulum are dilated by oxidizing agents. Of the several mounting media tested, Shear's mounting fluid was the best. This medium gave clearer mounts and produced the least distortion, although there was some variability owing to pH changes during mount preparation. This variable was controlled by preparing the medium with pH 8 McIlvaine's buffer. The method of mount preparation and the formula of the medium are presented as a suggested standard procedure for taxonomic studies on smuts. The standard temporary-mount procedure involving alcohol followed by potassium hydroxide and then heat should be discontinued, as hot alcoholic potash dissolves away sheath materials. Instead, Shear's mounting fluid should be employed. To obtain uniform dye uptake by smut spores in aqueous mounts they should be leached in ether or some other highly volatile lipoid solvent. Not only are dyes more readily absorbed, but they are absorbed at much lower concentrations. Several staining procedures and dye combinations are suggested to differentiate wall structures. However, an oil-bearing "mesospore" could be defined only in non-ether-leached spores.