. The cytoplasm of the plant cell. Plant cells and tissues; Protoplasm. Chapter XIII — 141 Vital Staining. The oxidation-reduction potential of neutral red scarcely per- mits this destaining to be attributed to a reduction of the dye and various experiments seem to indicate that yeasts do not reduce neutral red. The destaining of the vacuoles can only be explained, therefore, by assuming a destruction of neutral red, or an ex- cretion of it by the yeasts. The following experiment throws light on this problem. One half gram of Saccharomyces cerevisiae at a pH of 8 is sown in a big flask contain
. The cytoplasm of the plant cell. Plant cells and tissues; Protoplasm. Chapter XIII — 141 Vital Staining. The oxidation-reduction potential of neutral red scarcely per- mits this destaining to be attributed to a reduction of the dye and various experiments seem to indicate that yeasts do not reduce neutral red. The destaining of the vacuoles can only be explained, therefore, by assuming a destruction of neutral red, or an ex- cretion of it by the yeasts. The following experiment throws light on this problem. One half gram of Saccharomyces cerevisiae at a pH of 8 is sown in a big flask containing the medium described above to which of neutral red has been added. A sample of the liquid is taken at regular intervals and centrifuged. The sediment is examined under the microscope each time and the con- centration of neutral red of the liquid is measured by Meunier's photo-electric colorimeter. The experiment proved that, at the end of half an hour, all the cells accumu- lated neutral red in their vacuoles and that the concentration of the dye in the liquid was reduced from There is therefore a very great absorption of the dye by the yeast. At the end of half an hour, the vacuoles begin to lose their stain and the concentration of neutral red in the liquid again increases and finally at the end of an hour all the cells are destained and the concentration of the dye in the liquid has returned very nearly to its original amount. The vacuoles are then complete- ly destained. Now, various experiments having shown that under these conditions there is no absorption by the membranes of the cells, one is obliged to conclude that the yeasts, after having accumulated the neutral red in their vacuoles, excrete it into the medium. So it is only when they are freed of the dye that they begin to bud. Saprolegnia behaves differently from the yeasts, since it ac- cumulates neutral red while growing. Nevertheless it seems also to be able to excrete the dye under
Size: 1765px × 1415px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollection, booksubjectplantcellsandtissues
