The results of some experiments concerning the influence of growth substance on ion intake by plants are presented. Is has been found that the rate of ion intake is independent of low concentrations of growth substance. It is suggested that the intake takes place via the living processes. The regulation of the transport of glucose is mentioned as a possible direct function of the growth substance.
The intake of ions by the plant is a consequence of its reaction to the composition of the medium. As a base from which to start further research into this phenomenon, we suggested a working hypothesis founded upon the following concepts: — The ion absorption is a result of the differences in the physico-chemical activity of the ions of the periphery of the root and the ions of the medium. This difference in ion activity causes a flow of ions to move in the direction of the plant, which flow is kept going by transportation and inactivation of the ions taken up by the plant (pump-function).
A complication of the process in question arises from the adsorption of ions from the medium to the surface of the root (surface-function) (Schuffelen and Loosjes, Schuffelen). Energy is needed for the continuation of the pump-function and this is provided by processes taking place in respiration and in accumulation of organic material. It is consequently a function controlled by the living- processes (Hoagland and Steward, Lundegardh). The surface-function is of a more non-living nature and is regulated by the composition of the plasma of the root wall.
This plasma is highly important in connection with the study of the significance of the ion ratio of the medium in relation to plant growth, while the pump-function is related to the ion intake process as a whole. As plant growth substances play an important r61e in living processes it may be expected that the ion intake will also be influenced by auxin concentrations as suggested by Lundegrdh and others. Moreover, the fact that Veldstra considers the growth substances to act as transport (permeability) regulators encouraged us to examine the influence of some growth substances on ion absorption.
(Plant & Soil, 1948)