Under The Rose

[Brian D. McCary]

Just out of curiosity, does anyone know where the phrase "under the rose"
comes from?  Not only is it the title of one of TRP's short stories,
but it pops up early on in V:

"Profane had wondered then what it was with Da Conho and that machine
gun.  Love for an object, this was new to him.  When he found out not long
after this that the same thing was with Rachel and her MG, he had his first
intelligence that something had been going on *under the rose*, maybe for
longer than and with more people than he would care to think about."

My emphasis added.  I've never run across this phrase anywhere else.  
Any hints?

Brian McCary