Experiment to demonstrate positive phototropism in shoot tips
A darkened black box is taken having a small window on one side. A wellwatered potted plant is placed inside the box. This is referred to as a phototropic chamber or heliotropic chamber. If the window is kept closed for about 24 hours the plant shows normal growth. If the window is kept opened, it is found after two days that the shoot tip bends and grows towards light proving that it is positively phototropic (Figure 15.20).