Neville: You know, if you're interested in plants, you should use Goshawk's Guide To Herbology. There's someone in Tibet who's growing gravity resistant trees...
Harry: Neville, no offense, but I really don't care about plants. Now, if there's a Tibetan turnip that will help me breathe underwater for an hour, great. But otherwise...
Neville: I don't know about turnips, but you could always use gillyweed.