Thallus:
1. When the plant body is not differentiated into root, stem and leaves, it is called thallus. It is found in algae.
2. It is a gametophyte but reproduces both asexually and sexually.
3. Specialised sex organs, such as antheridium and archegonium are not formed.
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4. Gametes are mostly biflagelleted.
5. It may be unicellular or multicellular.
Prothallus:
1. It is a small, thallus-like green, flat and heart-shaped structure found in ferns.
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2. It is a gametophyte and reproduces only sexually.
3. Prothallus contains antheridium and archegonium.
4. Gametes are multiflagllated.
5. It is multicellular.