Passage of sugars across the plasmalemma of carrot callus cells

In pieces of carrot callus, the regions exterior to the plasmalemma were washed out in running tap-water within 15 min. The effect of temperature on sugar efflux and influx, suggests that the passage of sugars across the plasmalemma occurs mainly, if not entirely, by passive diffusion. The results of other workers are considered, and we conclude that the reported apparent active uptake across the plasmalemma may in reality have been due to active uptake across the tonoplast. Estimates of the apparent free space were unaffected by the sugar used, or the temperature, and we suggest that the apparent free space includes most, if not all of the metabolic compartment.