What occurs during the hydration phase after removing xylene?

During the hydration phase after removing xylene, washing the samples in decreasing alcohol concentrations occurs. This step is crucial because xylene is a non-polar solvent used to clear specimens after the embedding process. Prior to embedding the samples in paraffin wax, it's essential to rehydrate them, which is achieved by gradually decreasing the concentration of alcohol they have been immersed in.

Starting from a higher concentration of alcohol, which is used to remove xylene, the samples are subsequently transferred to solutions of lower alcohol concentrations, ultimately leading to an aqueous environment suitable for embedding in wax. This gradual transition helps prevent any damage to the tissues that could occur if it were done too abruptly.

The other options do not accurately describe the hydration phase after xylene removal: washing in increasing alcohol concentrations would not effectively rehydrate the tissue; transferring to a wax embedding medium happens after hydration; and staining the samples occurs after the embedding process, not during hydration.