George Edward Briggs

Membrane potential differences in Chara australis

The observations of Hope & Walker (1961) on the electric potential difference between the cytoplasm of cells of Chara australis and the external medium, when the ionic composition of the latter was varied, are considered in relation to a chloride, or sodium, pump with passive diffusion of potassium, sodium and chloride. The observations agree, atleast, as well with such a system as they do with the system suggested by Hope & Walker, which is restricted to passive diffusion of potassium and sodium.

Photosynthesis in Intermittent Illumination

The reduction of one molecule of carbon dioxide per two thousand molecules of chlorophyll after each intense flash of light of very short duration, while three hundred or m ore are reduced when the duration of the flash is greatly increased, can be explained by assuming that chlorophyll sensitizes the activation of a substance A which, by handing on its energy, causes the reduction of carbon dioxide in combination with a substance S. The decay of activated A is a relatively rapid process while that of the activated compound of carbon dioxide and S is relatively slow. The yield for short flashes is determined by A , that for long flashes by S. The ratio of to A is of the order of 100.

Salt Relations of Woody Tissues. II. Experiments with Lengths of Wood and Cut Leafy Shoots

The relationship between the concentration of a cation in the solution flowing from a length of wood from which the bark has been removed and time is compared with that expected on the assumption that the velocity of flow is uniform and that the constants for interchange between water free space (WFS) and Donnan free space (DFS) in the wood, established previously, apply. The difference is attributed to the variation of velocity of flow with diameter of the elements in the wood and resistance in cross-walls. Measurements of uptake of cations and anions into cut shoots show that the bulk of the supply to the bark is by way of the wood although there appears to be some movement other than diffusion in the bark. The relationship between the concentration of an ion and distance from the base is considered and an exponential fall is shown to be fortuitous.

Electro-Osmosis in Nitella

Electro-osmosis could occur through a composite membrane consisting of a porous wall with a continuous lining of lipid in which water and ions are soluble; pores right through are not necessary. The available information about the hydraulic permeability, the diffusional permeability and the conductance of the cell membrane in Nitella can be explained without making any unreasonable assumptions as to the properties of the wall and the lipid lining.