Originally posted in substantially similar form on September 24, 2010, at Historical Fancy Dress.
Jumping forward in time, from The New York Times on February 18, 1898 comes a full description of a very successful themed fancy dress event: a "Plant Party". The ladies were asked to dress in some "representative" costume, while the gentlemen were expected to appear in ordinary evening clothes and were given something like a vegetable boutonniere at the door. Supposedly, this was copied from something that Louis XVI did it at Versailles. I'd certainly like to see a description of that!
Sadly, very little information is given about the dancing: there was some, informal, after supper, and with no cotillion.
No full list of costumes was published, but there are some excellent examples at the end of how the ladies trimmed their gowns to match the theme.
I've transcribed the entire article below.

