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The effects of a non-ionic detergent. Triton × 100, on protoplasmic streaming in some plant cells, on plasmolysis, and on leakage of solutes from beet cells were investigated. The results of the different tests showed some features in common: (1) There is a critical range between 0.007 and 0.01 % v/v. (2) Above this concentration of the surfactant, that is at a concentration close to 0.01 %, the effect is manifested in the following ways. Plasmolysis with sucrose is anomalous or impossible. Protoplasmic streaming ceases within a short time. Definite leakage of ions and sugars starts from beet tissues. (3) At concentrations lower than 0.01 to 0.007 % there is enhanced retention of solutes in beet disks. — It is thought that the critical micelle concentration is of paramount importance. The micelle effect may consist in solubilizing or in forming mixed micelles or a complex with the globular lipoprotein units of the outermost plasma layer, the plasmalemma. The effect of the lower Triton concentrations is discussed.

Seeds of Lepidium and Sinapis were germinated and grown for 3 days in different concentrations of Triton X-100 (0.001–0.1 % v/v). The elongation of the primary root was slightly stimulated by low concentrations. In concentrations above 0.01 %, Triton inhibited root growth and forked root hairs developed. The hairs elongated both at the apex and at the base, exhibited protoplasmic streaming and activity of particulate non-specific esterase. In contrast the growth of the hypocotyl of both Lepidium and Sinapis diminished steadily in increasing concentrations of Triton. Triton also affected the percentage germination of Lepidium, which increased or decreased according to the concentration used. The changes in root growth and germination and the appearance of branched root hairs in abundance coincide with a change in the detergent solution from monomer to aggregated molecules.

In recent years there has been an increasing tendency to regard the tonoplast as the decisive diffusion barrier of the protoplast. The plasmalemma has been assumed to be more or less freely permeable, especially to ions (Brooks 4, Arisz 1, Epstein 8, Briggs and Robertson 3, Sutcliffe 12). This view is, however, based on observations which are far from unequivocal. In the following we shall try to elucidate the question of the relative permeability and susceptibility of the two plasma membranes towards sodium hydroxide and sodium carbonate. The tests were made on internodal cells of Nitellopsis obtusa, staminal hairs of Tradescantia virginiana and T. zcbrina and epidermal cells of Allium cepa var. sanguinetim. These cells show protoplasmic streaming and either contain anthocyanins or were stained with neutral red. In these experiments the plasmalemma, or some other layer outside the streaming part of the protoplasm, is assumed to be more or less impermeable towards sodium hydroxide as long as protoplasmic streaming is going on in the cells lying in the strongly alkaline solution. On the other hand, by the time the colour of the cell sap changes a considerable amount of NaOH must have passed through the whole protoplast, including both plasmalemma and tonoplast. The principal object of the experiments was, therefore, to compare (a) the time necessary to stop the protoplasmic streaming, irreversibly, with (b) the time required for the colour of the vacuole to change either to yellow (neutral red) or to blue (anthocyanin).