THE AUXIN-LIKE EFFECTS OF HUMIC PREPARATIONS FROM LEONARDITE
Humic acid is readily available from leonardite, a naturally occurring oxidized form of lignite coal. Humic materials have been found to greatly promote root initiation of Pelargonium hortorum cuttings. Sodium humate, humic acid, fulvic acid, and leonardite produced a proliferation of roots at optimum concentrations of 0.05%, 0.05%, 0.05%, and 0.5%, respectively. Pea root tip elongation measurements indicated that the humic materials possess auxin activity.