User blog comment:Ieatrice/New Image Galleries Available in Labs/@comment-11842624-20141015200439/@comment-3988575-20141017025136

On mobile, you are right, there is no hover. The user can tap on the caption and it will expand to show the rest of the caption. If you tap away from the caption, the caption will collapse again. One of the goals for the galleries is to offer some level of standardiziation for gallery styles so we don't plan on offering fine-tuning to each individual gallery at this time.