WATER UPTAKE AND ROOT GROWTH AS INFLUENCED BY INEQUALITIES IN THE CONCENTRATION OF THE SUBSTRATE

When a number of solutions of unlike concentration are presented at one and the same time either to an established or to a developing root system, questions follow as to whether water is withdrawn as rapidly from the concentrated as from the dilute regions and as to whether new roots extend themselves as readily in the regions of high salinity as in those of low salinity. The subject is of agronomic, as well as physiological, significance since the productivity of soils must be regarded as being contingent not only on their nutrient and water storage resources but also upon the readiness with which these resources can be utilized by plants. A substantial diversity is customarily found in the salt concentrations of the soil solution within the root zone of single plants growing on irrigated lands. The data of table I, which are presented as an illustration, represent