The Effect of Acetate Buffer Mixtures, Acetic Acid, and Sodium Acetate, on the Proto- Plasm, as Influencing the Rate of Penetration of Cresyl Blue into the Vacuole of Nitella. by Marian Irwin

An adequate theory of the penetration 1,~,3 of cresyl blue into the vacuole of living cells of the fresh water plant Nitella may be stated as follows. The dye, in form of free base, which predominates at a high pH value, diffuses in and out of the vacuole very freely, while the dye in form of salt, which predominates at a low pH value, diffuses so slowly that its rate of penetration and that of the exit may be neglected in experiments of the present type. Upon the entrance of free base into the vacuole it is partly converted at once into the salt (the extent depending on the condition of the sap, i.e. the pH value). The concentration of free base inside the vacuole is always proportional to that of the free base in the external solution. We may picture the entrance of dye into the vacuole as a reversible process ~ depending primarily on the diffusion of free base through a very thin layer of protoplasm which lies between the cell wall and an inner central vacuole filled with aqueous sap (at about pH 5.5 and containing about 0.1 M halides). The consideration of cell wall may be neglected since the substances in this case do not seem to affect it enough to change the rate of penetration of dye into the vacuole.