An investigation of the staining reactions of ascospores from 10 species of yeasts with 19 different dyes, showed that differentiation of spores from vegetative cells by staining depends on their relative permeability properties. Three possible staining mechanisms are discussed and examined for consistency with the data. It was also discovered that ascospores of ttansenula saturnus, which are not stained by the malachite green method, could be differentiated very satisfactorily from the vegetative cells by staining with hot rose bengal, followed by counterstaining with cold victoria blue B.
It is well known that certain procedures used for staining bacterial spores are also effective in differentiating the ascospores of some yeasts from the vegetative cells. B~Auv~nI~ (1917), applying the Ziehl-Neelson acid-fast staining technique, found satisfactory differential staining of the spores of Saccharomyce8 sl0p., although it was unsuccessful with those of Schizosaccharomyces oetosporus. He attributed this staining reaction to the stronger acid-fast properties of the spore. A similar procedure also involving decolourization with acid has been described by ARNOLD (1938) and LINI)~Ga~N (1949). Similarly, SmMW~LL (1938) and later ~cCLuNG (1943) discovered that the Schaffer-Fulton method for staining bacterial spores was also successful with Saccharomyees. It is not, however, equally effective with all yeasts, since spores of Hansenula saturnus remain unstained (WIcK~RI~A?a, 1951). This technique is similar to the Ziehl-Neelson method in that the first dye applied is hot, and counterstaining is carried out at room temperature, but there is no decolourization in acid, water alone being used for washing. This suggests that acid-fast properties are not in fact responsible for the staining of yeast spores.
In order to interpret some effects of visible radiation on the staining properties of yeast ascospores (KELLY and GAg, 1969), it was essential to discover the mechanism by which undamaged spores are differentiated