In fern, archegonia occur on

Options

A. Stem
B. Root
C. Leaf
D. Sex organ.

Answer

### Step-by-Step Solution:

1. **Understanding Ferns**: Ferns belong to the group of plants known as pteridophytes, which are seedless vascular plants. This means they have a vascular system for transporting water and nutrients but do not produce seeds.

2. **Identifying Archegonia**: Archegonia are the female reproductive structures in ferns. They are responsible for producing eggs.

3. **Location of Archegonia**: In ferns, archegonia are found on the gametophyte stage of the plant, which is known as the prothallus. The prothallus is a heart-shaped, free-living structure that develops from haploid spores.

4. **Prothallus and its Functions**: The prothallus bears both male and female sex organs: antheridia (male) and archegonia (female). The archegonia are specifically located on the prothallus.

5. **Conclusion**: Since the prothallus is derived from the spores that germinate from the sporangia located on the undersurface of the fern leaves, we can conclude that archegonia occur on the leaves of the fern, specifically on the prothallus.

6. **Final Answer**: Therefore, the correct answer to the question "In fern, archegonia occur on" is **leaf** (option 3).