Wash japonicas, but do not peel or core. Put into a preserving pan or large saucepan with the water (if the fruit is under-ripe add an extra ¼ pint water) and ginger. Simmer gently until the mixture is a pulp. Sieve the pulp and to each 1 lb. of pulp add 1 lb. sugar and the juice of 2 lemons. Put over a low heat until sugar has dissolved, then boil rapidly until setting point is reached. Pour into hot sterilized jars and cover.