Explain the experiment to measure the actual longitudinal growth with diagram.

The apical region of shoot and root have apical meristem. This region is responsible for the growth in the length of the plant. To measure the increase in the length of the plant, an instrument called lever auxanometer is used. It measures the rate of growth of plant. The auxanometer comprises of a movable pointer which is attached to a pulley and a graduated arc fixed to a stand. A thread passes around the pulley. One end of the thread is tied to the growing tip of the plant and the other end is tied to the small weight. As the plant grows, the pulley rotates and the needle moves down the scale. This helps to measure the growth in terms of length of the plant.