The growth of pollen tubes towards ovules is due to

Options

A. hydrotropism
B. chemotropism
C. geotropism
D. phototropism

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question:** The question asks about the reason for the growth of pollen tubes towards ovules.

2. **Identifying the Process:** The growth of pollen tubes is a response to certain stimuli. In this case, it is important to recognize that pollen tubes grow towards ovules, which is a crucial step in the fertilization process.

3. **Role of Chemicals:** The growth of pollen tubes is induced by the secretion of specific chemicals. These chemicals are primarily sugary substances secreted by the ripened stigma of the flower.

4. **Mechanism of Growth:** The sugary substances act as a stimulus for the pollen grains. The pollen grains respond to this chemical stimulus by growing a pollen tube in the direction of the ovule.

5. **Terminology:** The movement of the pollen tube towards the ovule due to the chemical stimulus is known as **chemotropism**. This term refers to the directional growth of an organism in response to a chemical gradient.

6. **Differentiating Other Tropisms:** It is important to distinguish chemotropism from other types of tropisms:
- **Hydrotropism**: Movement in response to water.
- **Geotropism**: Movement in response to gravity.
- **Phototropism**: Movement in response to light.

7. **Conclusion:** Based on the understanding of the process and the definitions of the different types of tropisms, the correct answer to the question is **chemotropism**.

**Final Answer:** The growth of pollen tubes towards ovules is due to **chemotropism**.

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