Prepare the artichokes. Break off the stems and pull off a the bottom row of leaves, close to the stem, if you can. Using a very sharp knife, and holding it against the side of the artichoke, cut off all the large leaves from the artichoke, leaving a soft cone of small leaves in the center. Cut off this soft cone of leaves, level with the artichoke heart. Scoop out any choke in the center, using a stainless steel spoon, and rub the artichoke heart all over with the lemon, to minimize discoloration. Trim the base of the heart into an even round shape. Rub again with lemon, and put the artichoke into the bowl of acidulated water.