The instrument by which the rate of growth of stem is accurately measured is
Or
Growth in length of a plant can be measured by

Options

A. Manometer
B. Auxanometer
C. Potometer
D. Clinostat.

Answer

To determine the instrument used to accurately measure the rate of growth of a stem or the growth in length of a plant, we can analyze the given options:

1. **Manometer**: This instrument is primarily used to measure pressure, not plant growth. It consists of a U-tube filled with a liquid, typically mercury, and is not relevant to measuring plant growth.

2. **Oxanometer**: This is the correct instrument for measuring the growth of plants in terms of length. The oxanometer works by using a thread that is passed over a pulley. One end of the thread is attached to the tip of the plant, while the other end is tied to a weight. As the plant grows, the thread pulls the weight, causing a deflection that can be read on a graduated arc. This deflection indicates the increase in the length of the plant.

3. **Potometer**: This device measures the rate of water uptake by a plant, specifically a leafy shoot. It is not used for measuring growth in length.

4. **Clinostat**: This is a device that rotates slowly and is used to study tropisms in plants by providing stimuli from all directions. It does not measure growth in length.

Based on the analysis of each option, the correct answer is:

**The instrument by which the rate of growth of a stem is accurately measured is the Oxanometer.**