"Roots are positively geotropic." The exception to this statement is

Options

A. pneumatophores in Rhizophora
B. stilt roots in sugarcane
C. prop roots in banyan
D. nodulated roots in legumes

Answer

**Step-by-Step Solution:**

1. **Understanding Geotropism**:
- Roots are generally described as positively geotropic, meaning they grow downward in response to gravity. This characteristic helps them anchor the plant and access water and nutrients from the soil.

2. **Identifying Exceptions**:
- While most roots grow downwards, there are exceptions where roots may grow upwards or in a different direction. We need to identify these exceptions.

3. **Analyzing the Options**:
- **Option 1: Nematophore in Rhizophora**:
- Nematophores are specialized aerial roots found in mangrove plants like Rhizophora. They grow upwards to access oxygen in waterlogged soils where oxygen is scarce. This is a valid exception to the statement.
- **Option 2: Slit Root in Sugarcane**:
- Slit roots grow from the base of the plant and do not exhibit upward growth. This option does not represent an exception.
- **Option 3: Supporting Roots in Banyan**:
- These roots grow downwards from branches to support the tree. They do not contradict the statement about geotropism.
- **Option 4: Nodulated Roots in Legumes**:
- These roots host nitrogen-fixing bacteria and typically grow downwards as well. This option also does not represent an exception.

4. **Conclusion**:
- The only valid exception to the statement "Roots are positively geotropic" is **Nematophore in Rhizophora**.

**Final Answer**: Nematophore in Rhizophora.

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