1. In a small saucepan, combine 1 cup of cold water, ˝ teaspoon of salt and the watercress or spinach leaves. Bring to a boil over high heat and boil 1 minute. Drain through a sieve and set the leaves aside.
2. In a 2-quart saucepan, combine the 6 cups of cold water, the kombu and the clams. Bring to a boil over high heat, then remove the kombu with a slotted spoon or tongs, and discard it.
3. Let the soup boil for about 2 minutes, or until the clams open, meanwhile skimming off any scum that rises to the surface. Stir in the mushrooms, soy sauce, ˝ teaspoon salt and a few sprinkles of MSG. Boil for 30 seconds, then remove from the heat.
4. In each of 6 soup bowls place 2 clams in their shells. Garnish with 2 sprigs of the watercress or spinach, a mushroom and a slice of lemon or lime.
5. Fill each bowl with the hot broth, pouring it down the side of the bowl to avoid disturbing the decorative arrangement. Serve at once.
