Which of the following characteristic structure is found in slime mould?

The correct answer is Capillitium.

Let's break down the explanation and look at the characteristics of slime moulds step-by-step:
1. What are slime moulds? Slime moulds (specifically myxomycetes or acellular slime moulds) are eukaryotic organisms that can live freely as single cells, but can aggregate together to form multicellular reproductive structures. During their reproductive stage, they form sporangia (fruiting bodies) containing spores.
2. What is a capillitium? A capillitium is a network of sterile, thread-like fibers found inside the sporangia of many myxomycetes (slime moulds), intermingled with the spores.
3. Function of the capillitium: The capillitium is hygroscopic in nature. It responds to changes in environmental humidity by twisting, expanding, or contracting, which helps in loosening the spore mass and aids in the gradual dissemination (dispersal) of spores into the wind.
4. Why other options are incorrect:
- Pseudoelaters: These are sterile cells found in the sporangia of hornworts (bryophytes, e.g., Anthoceros) that help in spore dispersal.
- Elaters: These are specialized, hygroscopic, spindle-shaped cells found in the sporangia of liverworts (bryophytes, e.g., Marchantia) that assist in spore discharge.
- Capitulum: This term refers to a type of head-like inflorescence found in flowering plants (like Asteraceae) or a structure in certain algae, but is not a characteristic spore-dispersal structure of slime moulds.