IN a recent paper, Galston 1 has shown that βindoleacetic acid, at concentrations of 1–10 p.p.m., inhibits the growth in the dark of excised stem tips ... at a concentration of 0.5 p.p.m ...

In a stem, the cells on the shaded side contain more auxin and grow longer than the cells on the light side. This causes the stem to grow towards the light. It is vital to note that the plant does ...