Hormogonia are produced in
A. Oscillatoria
B. Ultrix
C. Spirogyra
D. Yeast

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Hint: The cells of certain organisms produce filament during the vegetative reproduction. These filaments are referred to as hormogonia. These are produced during unfavorable conditions on exposure to environmental stress.

Complete Answer:
- In the given question, we need to discuss which organism produces hormogonia. It is produced by organisms that belong to the group of cyanobacteria. These organisms that produce hormogonia are known as filamentous cyanobacteria. Since oscillatoria are the blue-green algae which are capable of producing their food through the process of photosynthesis. These algae possess a special pigment called chlorophyll which is responsible for the photosynthesis process.
- We know that Oscillatoria belongs to the category of cyanobacteria from the above-given options. We should note that these organisms are present in freshwater. These organisms undergo reproduction through the process of fragmentation. We should note that fragmentation is the process that forms shorter filaments and these filaments get separated as fragments and grow as new younger ones. The broken filaments produced by oscillatoria are referred to as hormogonia. The length of these hormogonia structures varies depending on the particular organism which produces it.
- There are some additional points about oscillatoria discussed below. An interesting fact about oscillatoria is as its name signifies that these organisms are subjected to back and front movements known as oscillation. The part which is responsible for the oscillatory movement is the trichome. These trichomes are made of a set of cells whose tips are involved in the oscillatory movement.

So, the correct option is A as we know that hormogonia are the reproducing structures in the cyanobacteria, and out of all the options, Oscillatoria produces hormogonia during the vegetative reproduction process.

Note: It is noted that filaments are present in the cyanobacteria called trichomes. In between trichomes 5-15 cells are called hormogonia. This is a structure that firstly remains attached to the plant but after some time it gets separated and then leads to the formation of a fully-fledged filament.