The Relationships between Transpiration and Potassium Uptake inRicinus communis

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Abstract
The water uptake by individual water-culture-grown castor-oil plants (Ricinus communis) was varied and corresponding rates of potassium uptake measured. The water flux was varied by changing the rate of transpiration or by detopping the transpiring plants. Transpiration was altered by changing the atmospheric humidity at constant temperature and light intensity in a climatological wind tunnel. It was found that the uptake of potassium was divisible into two components: (a) an accumulation by the cells of the root and (b) a passage through the root to the shoot via the vessels. These components were found to be entirely independent of one another. Also while (a) was unaffected by the water flux (b) was linearly related to it. The concentration of potassium in the vessels was between 15 and 26 times that of the medium and this ratio which was found to be similar in both intact and detopped exuding plants remained constant in the face of wide changes in water flux. This essential similarity between exuding and transpiring plants and the finding that there was a lag between the change in water flux and the response in potassium uptake indicated that there is no continuous mass-flow pathway between medium and xylem in these plants. Instead, increased transpiration seems in some way to increase the rate of the exudation process. These conclusions are discussed in relation to the results of other workers.