The relationship between the rate at which water and the rubidium and phosphate ions are absorbed by intact plants, and transferred to their shoots has been investigated in water culture under varying conditions of transpiration and nutrient supply.

When the external concentration and the nutrient status of the plants are sufficient low, wide variations in the rate of transpiration have little effect on the transfer of nutrients to shoots; when little water is being lost by transpiration the concentration in the transpiration stream may exceed that in the external medium by factors exceeding 100. In contrast when the external concenration and the nutrient status of the plants are high the rate of transfer of ions to shoots may vary closely with the rate of transpiration and the concentration in the transpiration stream may be similar to, or less then, that in the external medium.

The occurrence of concentrations of ions in the roots is transpiration stream which greatly exceed those in the medium external to the roots is regarded as evidence that ions not transferred passively across the roots of intact plants to a significant extent.