Florists, nurserymen and gardeners are deeply interested in recent discoveries that certain chemical compounds, when absorbed into the appropriate living plant tissues, induce or stimulate the initiation of roots. Depending on species, point of application of the chemical and various environmental conditions, roots appear on stems or leaves at points where roots do not ordinarily arise. The chemicals used have been variously designated by different investigators as growth substances (6), hormones (3), phytohormones (28) and auxins (28). When applied to the rootage of cuttings, these substances may have a wide practical use.

Some of the most effective growth substances are offered to the trade under proprietary names. This bulletin deals with a series of experiments designed to test, under Iowa conditions, the efficacy of Hormodin A, a widely distributed trade product known to contain an effective growth-promoting chemical, indolebutyric acid, for the rooting of cuttings of many species and varieties of horticultural plants. The project was sponsored by the Boyce Thompson Institute for Plant Research, located at Yonkers, N. Y., under a cooperative agreement with the Iowa Agricultural Experiment Station. The study covered a period of 2 years and included tests with approximately 50 species and varieties. The immediate objectives of the research were: 1. To discover the most effective concentration of Hormodin A for the rooting of each species or variety; ~. to determine the effect of the treatment on cuttings taken at different stages of maturity; 3. to determine the reaction of cuttings taken at different seasons of the year to the treatments.