Acidity of the Medium and Root Production in Coleus

Abstract

IN order to test the effect which the reaction of the medium has upon root-production by cuttings, experiments have been made during the summers of 1924 and 1925 with Coleus. It is the practice at the Royal Botanic Garden, Edinburgh, to root in cocoa-nut fibre cuttings which require heat. It was found that the fibre gave a reaction of pH 4.5–4.7, and was very strongly buffered, large additions of acid or alkali being necessary to shift the pH appreciably. (The testing was done with the B.D.H. Capillator, the brown colour of the water squeezed from the fibre causing little trouble in the capillary tube.) In view of this marked buffer action, it is not possible to use this natural fibre for experiment, though it is excellent in practice, being of a light texture and holding a good amount of water without becoming sodden. An artificial medium, comparable to the natural fibre in physical state, of which the reaction can be controlled, has yet to be found. Sand, cotton-wool, and glass-wool, with water, and water alone were tried; only the last proved satisfactory. Experiments were accordingly made with tap-water, adjusted to the required pH by the addition of traces of hydrochloric or sulphuric acids or of sodium carbonate, the normal pH of the water being about 7.3. While these results cannot be directly transferred to the case of fibre, owing to the great differences in oxygen supply, they are at least suggestive.