To be unusually Frank about it, orangetruck, when I first saw this expression of Proulx's, I immediately associated the word "rose" with the anus, and stem (as a noun and not a verb) for you know what. Hence, I thought there was a double meaning to the term -- first, it meant taking the thorns out of the rose, and second... well, you know what.
I interpreted it as a deliberate play at words.