Been away for a while. Thought maybe you were going to say I haven't mentioned the missing comma from the clue, too.
I have read a bit of JS Mill, so this caught my eye. Must admit, though, i still haven't worked out why the best = flower (no River Best as far as I know so must be something else)
2.
the finest individuals out of a number of people or things.
"he wasted the flower of French youth on his dreams of empire"
synonyms: best, finest, top, pick, choice, choicest, prime, cream, prize, treasure, pearl, gem, jewel, the jewel in the crown, the crème de la crème, first class, elite, elect; informalthe tops
"the flower of the nation's youth"