Which of the following plants do not contain Rhizobium in their root nodules ?

Options

A. Alfalfa and sweet clover
B. Sweet pea and lentils
C. Alnus and Casuarina
D. Garden pea & broad bean

Answer

To determine which of the following plants do not contain Rhizobium in their root nodules, we need to understand the relationship between Rhizobium and various plant types, particularly focusing on leguminous plants.

### Step-by-Step Solution:

1. **Understand Rhizobium**: Rhizobium is a genus of gram-negative bacteria that forms a symbiotic relationship with certain plants, particularly leguminous plants. This relationship is important for nitrogen fixation, which is crucial for plant nutrition.

2. **Identify Leguminous Plants**: Common examples of leguminous plants include peas, soybeans, and alfalfa. These plants typically contain Rhizobium in their root nodules.

3. **Analyze the Options**:
- **Option 1: Alfalfa and Seed Clover**: Both are leguminous plants and therefore contain Rhizobium.
- **Option 2: Sweet Plain Lentils**: This is also a leguminous plant and contains Rhizobium.
- **Option 3: Alnus and Caterina**: Alnus (commonly known as alder) is not a leguminous plant and does not contain Rhizobium in its root nodules. Caterina is not a recognized leguminous plant either.
- **Option 4: Carton Plant**: This is also not a leguminous plant and does not contain Rhizobium.

4. **Conclusion**: Among the options provided, Alnus and Caterina do not contain Rhizobium in their root nodules. Therefore, the correct answer is **Alnus and Caterina**.