Abstract
The effects of external H-ion conc. within the range of pH 3 to 9, on the growth of Lycopersicum esculentum, Lactuca saliva, and Cynodon dactylon were studied by means of a special water-culture technique. The essential features of the technique provided for the maintenance of the same conc. of Ca, Mg, K, nitrate and phosphate ions as well as for the availability of Fe and Mn throughout the entire pH range. Profoundly adverse effects of external pH, treated as an isolated variable, were found only at extremes of acidity or alkalinity. Complete failure of growth occurred at pH 3 and a marked decline at pH 9, but within a relatively wide range of pH between 4 and 8, fluctuations in the pH were tolerated by the plants provided an adequate supply of all nutrient elements was maintained. At pH 4 and 5, the growth of lettuce and tomato was favorably affected by increasing the conc. of Ca in the nutrient soln. At pH 6, however, the growth obtained at low and high conc. of Ca was equally favorable. With the possible exception of extremes unfavorable for growth, the external reaction had no significant effect on the pH of the expressed sap of either shoots or roots.