Some pH Changes in Nutrient Solutions

1. The culture media used generally for the asymbiotic germination of orchid seeds are so weakly buffered that, as the seedlings start to grow, the pH value drops below the level for optimum growth. Even when the phosphate buffer was increased twenty-four fold, the buffering action was still weak in the optimal growth range of pH 4.5-5.5, indicating that phosphate buffers are unsatisfactory. An investigation indicated that amino acids are excellent buffers. This work is being continued to determine what amino acids will be satisfactory not only as buffers but also as growth factors. 2. Autoclaving the culture media without agar produced significant changes in pH value. Similar changes in pH value were observed, only at a slower rate, when the solutions stood for some time. These results are equally applicable to ordinary nonsterilized culture media. The changes when the original pH value was 3 to 6 were due to the presence of iron sulfate, which should be replaced by one of the organic iron salts; when it was between pH 6 and 9, the changes were due to the presence of calcium nitrate. Based on these studies a new nutrient solution is proposed.