The growth in plants in measured by
Pfeiffer's auxanometer
Osmometer
Manometer
Respirometer

Options

A. Pfeiffer's auxanometer
B. Osmometer
C. Manometer
D. Respirometer

Answer

To determine how growth in plants is measured, we need to analyze the options provided:

1. **Pfeiffer's Auxanometer**: This device is specifically designed to measure the growth of plants. It measures the increase in length of the plant over time. The auxanometer typically consists of a pulley system where one end of a thread is attached to the tip of the plant, and the other end has a weight. As the plant grows, the movement of the plant causes the pointer to indicate the growth measurement.

2. **Osmometer**: This device is used to measure osmolality, which refers to the concentration of solute particles in a solution. It is not related to measuring plant growth.

3. **Manometer**: A manometer is used to measure the pressure of gases or liquids. It does not measure plant growth.

4. **Respirometer**: This device measures the rate of respiration in organisms, including plants, but it does not measure growth directly.

Based on this analysis, the correct answer is **Pfeiffer's auxanometer**, as it is the only device specifically designed to measure the growth of plants.

### Step-by-Step Solution:
1. **Identify the devices listed**: Look at each option provided (Pfeiffer's auxanometer, osmometer, manometer, respirometer).
2. **Understand the function of each device**:
- **Pfeiffer's Auxanometer**: Measures plant growth.
- **Osmometer**: Measures osmolality.
- **Manometer**: Measures pressure.
- **Respirometer**: Measures respiration rate.
3. **Determine which device is relevant to plant growth**: Analyze which device specifically measures growth in plants.
4. **Conclude the answer**: Based on the analysis, conclude that Pfeiffer's auxanometer is the correct answer.