On the Accumulation of Dye in Nitella. by Marian Irwin.*

The large mnltinucleate cells of Ni~l la (about four inches in length) afford good opportunities for the study of permeability, and have therefore been used in the experiments described in this paper. The cell consists of a cell wall of cellulose, inside which is a thin layer of protoplasm surrounding a large central vacuole filled with sap which has a streaming movement. Analysis 1 of the sap has shown that the cell has the power to store up halides to a remarkable degree so that they reach a concentration of a little over 0.1 ~, while only a trace is present in the water in which the cell lives. The halides in the sap do not seem to come out of the vacuole unless the cells are injured or plasmolyzed. Not only the halides but many other substances are stored up in this manner3 The writer has found that the young cells (one-half an inch in length) have the same concentration of halides as older cells (about six inches in length). What is the explanation of the mechanism of storage? Is the determining factor physical or chemical? Does it lie in the cell wall, in the protoplasmicdayer, or in the cell sap? The only way to answer these questions is to analyze the process step by step. To do this it is necessary to use a substance which readily accumulates in the cell sap to a considerable extent without producing injury. Since only small quantities of sap are available, the substance chosen must be capable of easy and accurate measurement