Question

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

Answer 1

Auxanometer as the name suggests auxin means "to grow" and metron means "measure". Increase in growth of plants is measured with the help of apparatus known as the auxanometer.

Complete answer:
Apical meristem is present at the apex of the roots and shoots. The plant growth occurs from this region. The apical regions of shoot and root have apical meristem. This region is responsible for the growth in the length of the plant. Auxanometer can be used for the measurement of rate of longitudinal growth in plants. These are the simple instruments which measure the growth by recording the increment in length. The auxanometer which is used most commonly is known as the arc auxanometer.
The set up comprises a wire whose one end is fixed to the plant apex while at the other end a dead weight is tied. This wire is then passed over a pulley having a movable pointer. An arc is fixed at a stand. The pulley is rotated as the plant grows moving down the needle along the circular scale thus providing the growth magnitude. This helps in the measurement of length of the plant thus determining its growth.
The length of plant growth that is measured through an auxanometer could be divided with the time taken for the respective measurement in order to derive the rate of growth.

Note: A very little growth (even in micrometers) could be measured using a sensitive auxanometer. These auxanometers could be used in the field, laboratories and even in the classroom. These are sometimes also referred to as an arc-indicator.