Which of the following is not a growth-measuring instrument?

Options

A. Auxanometer
B. Crescograph
C. Horizontal microscope
D. Clinostat

Answer

To determine which of the following options is not a growth-measuring instrument, let's analyze each of the provided options:

1. **Oxonometer**: This instrument is used to measure the growth of plants by assessing their oxygen consumption. It is indeed a growth-measuring instrument.

2. **Crescograph**: This device was invented by Sir Jagdish Chandra Bose and is specifically designed to measure the growth of plants over time. It is a well-known growth-measuring instrument.

3. **Horizontal Microscope**: This instrument is used to observe and measure the growth of plants at a microscopic level. It is also considered a growth-measuring instrument.

4. **Clinostat**: The clinostat is an instrument used to study the effects of gravity on plant growth rather than measuring growth itself. It helps in understanding how plants respond to gravitational forces, but it does not measure growth directly.

Based on this analysis, the instrument that is not primarily a growth-measuring instrument is the **Clinostat**.

### Final Answer:
The correct option is **Clinostat**.