A commercial horticulturist investigated the effect of different concentrations of indole-3-butyric acid (IBA), a synthetic auxin rooting hormone, on the rooting success of stem cuttings from a specific cultivar of rose (Rosa rubiginosa).
For each concentration tested, 20 stem cuttings of equal length were treated and planted. The table below shows the number of cuttings that successfully developed roots after 28 days.
| Concentration of IBA (ppm) | Number of stem cuttings treated | Number of cuttings with successful root development after 28 days |
|---|---|---|
| 0 (Control) | 20 | 3 |
| 50 | 20 | 3 |
| 100 | 20 | 11 |
| 200 | 20 | 20 |
| 400 | 20 | 14 |
State and explain the conclusions the horticulturist can make from these results.
