Negative geotropic roots of mangrove plants are :

Question

Accepted Answer

Negative geotropic roots of mangrove plants are known as pneumatophores, which is why Option 4 is the correct answer. Let's delve into the explanation:

1. **Why Option 4 is Correct (Pneumatophores):**
   - Pneumatophores are specialized aerial roots that grow upwards, against the force of gravity, which is why they are termed "negative geotropic." These roots are a characteristic feature of mangrove plants, which thrive in waterlogged, oxygen-poor environments such as coastal intertidal zones.
   - The primary function of pneumatophores is to facilitate gas exchange. They protrude above the water or soil surface, allowing the plant to access atmospheric oxygen, which is crucial for respiration in the anaerobic conditions of waterlogged soils.
   - This adaptation is vital for the survival of mangrove plants, as it enables them to thrive in challenging environments where other plants might not survive.

2. **Why the Other Options are Incorrect:**
   - **Option 1: Coralloid roots**
     - Coralloid roots are typically associated with cycads, not mangroves. These roots have a symbiotic relationship with nitrogen-fixing cyanobacteria, which help in nitrogen assimilation. They do not exhibit negative geotropism and are not related to the oxygenation needs of mangroves.
   
   - **Option 2: Assimilatory roots**
     - Assimilatory roots are involved in photosynthesis and are not a feature of mangrove plants. These roots are not adapted for gas exchange in waterlogged conditions and do not exhibit negative geotropism.
   
   - **Option 3: Hygroscopic roots**
     - Hygroscopic roots are specialized for absorbing moisture from the air, typically found in epiphytic plants. They are not relevant to the mangrove environment and do not exhibit the negative geotropic growth pattern seen in pneumatophores.

In conclusion, pneumatophores are the correct answer as they are uniquely adapted to the environmental conditions faced by mangrove plants, allowing them to access oxygen in waterlogged soils through their negative geotropic growth.