Read the following text and answer the following questions on the basis of the same:
A typical anther is bilobed. It is a tetragonal structure consisting of four microsporangia. These microsporangia form pollen sac which on maturity gets filled with a pollen grains. Pollen grains represent the male gametophytes, their cell wall is very hard. Pollen grains of many species cause severe allergies which cause various diseases in human beings.
Assertion (A) : The innermost layer of microsporangium is called tapetum.
Reason (R) : Tapetum nourishes the develop into pollen grains.

Options

A. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
B. Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
C. Assertion (A) is true but reason (R) is false.
D. Assertion (A) is false but reason (R) is true

Explanation

To solve the question based on the provided text, we will analyze the assertion and reason statements step by step.

### Step-by-Step Solution:

1. **Identify the Assertion and Reason:**
- Assertion (A): The innermost layer of microsporangium is called tapetum.
- Reason (R): Tapetum nourishes the developing pollen grains.

2. **Evaluate the Assertion:**
- The text describes the structure of a typical anther, stating that it consists of four microsporangia. The innermost layer of the microsporangium is indeed called the tapetum. Therefore, the assertion is **true**.

3. **Evaluate the Reason:**
- The reason states that the tapetum nourishes the developing pollen grains. In the context of the microsporangium, the tapetum provides nutrients to the developing pollen grains, which is also **true**.

4. **Determine the Relationship Between Assertion and Reason:**
- While both the assertion and reason are true, we need to assess whether the reason is the correct explanation of the assertion. The assertion states what the innermost layer is called, while the reason explains its function. Although the reason is true, it does not directly explain why the innermost layer is called the tapetum. Thus, the reason is **not the correct explanation** of the assertion.

5. **Conclusion:**
- Since both the assertion and reason are true, but the reason does not correctly explain the assertion, the correct option is: "Both assertion and reason are true, but reason is not the correct explanation of assertion."

### Final Answer:
The correct answer is: **Both assertion and reason are true, but reason is not the correct explanation of assertion.**