STUDIES ON THE pH‐RELATIONSHIPS OF ROOT GROWTH AND ITS INHIBITION BY 2:4‐DICHLOROPHENOXYACETIC ACID AND COUMARIN

4-5-8-8, the final total concentration in the culture medium being 0-015 M. With these concentrations normal growth was obtained, but over the experimental growth period (5-6 days) considerable drifts in the pH were recorded by measurements of initial and final values with a Beckman pH meter using a glass electrode. These shifts were greatest at the alkaline end of the pH range. Typical results for such an experiment for a 7-day growth period are seen in Fig. The S-shaped curve seen here is a reflexion of the falling-off of buffering capacity at the two extremes of the pH range, the point of inflexion occurring at roughly the theoretical value of 6-8. In addition, however, there is a bodily shift of the whole curve in a direction of increased acidity, due probably to an accumulation of respiratory CO2 in the medium.