Choose the correct statements. 
1. Autogamy takes place only in cleistogamous flowers. 
II.  A plant with geitonogamy must possess unisexual flowers.
III. Allogamy takes place only in chasmogamous flowers 
IV. A dioecious plant is always xenogamous

Options

A. I, II, III, IV
B. I, III, IV
C. II, IV
D. III, IV

Answer

To determine which statements are correct regarding autogamy, geitonogamy, allogamy, and dioecious plants, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement I: Autogamy takes place only in cleistogamous flowers.**
- **Analysis:** Autogamy refers to self-pollination, where pollen from the same flower fertilizes its ovules. While cleistogamous flowers (which remain closed) primarily exhibit autogamy due to their structure, autogamy can also occur in chasmogamous flowers (which are open) under certain conditions. Therefore, this statement is **incorrect**.

2. **Statement II: A plant with geitonogamy must possess unisexual flowers.**
- **Analysis:** Geitonogamy is a form of pollination where pollen from one flower fertilizes the ovules of another flower on the same plant. This can occur in both unisexual and bisexual flowers. Thus, it is not necessary for geitonogamy to involve only unisexual flowers. Therefore, this statement is **incorrect**.

3. **Statement III: Allogamy takes place only in chasmogamous flowers.**
- **Analysis:** Allogamy refers to cross-pollination, where pollen from one plant fertilizes the ovules of another plant. This process requires the flowers to be open (chasmogamous) to allow pollen to be transferred between different plants. Therefore, this statement is **correct**.

4. **Statement IV: A dioecious plant is always xenogamous.**
- **Analysis:** Dioecious plants have distinct male and female individuals, meaning that male plants produce only male flowers and female plants produce only female flowers. As a result, for fertilization to occur, pollen must be transferred from a male flower to a female flower of another plant, which is a form of xenogamy (cross-pollination). Therefore, this statement is **correct**.

### Conclusion:
The correct statements are:
- Statement III: Allogamy takes place only in chasmogamous flowers.
- Statement IV: A dioecious plant is always xenogamous.

Thus, the correct answer is **Statements III and IV**.