Prepared formulations are also available if propagators do not wish to make their own rooting preparation, but the concentrations available may not be the optimum for many plants. The existence of plant hormones first demonstrated by Charles Darwin - end of 19th century. Studying phototropism - bending towards light. Used canary grass and its coleoptile. Coleoptile will bend towards a unidirectional light source.
Tip perceives light - cover tip with foil, and no bending.
Since region of bending below the tip, concluded that a substance is produced in the tip and transported to the region of bending. Coleptile bends because the growth of cells under the agar block is stimulated. Angle of curvature proportional to number of coleoptiles stood on agar. Later discovered substance was auxin. Found that the degrees curvature proportional to the amount of auxin in the agar block.