Cut plums from stones; crush in blender, or chop fine.
Measure fruit into saucepan, and add water.
Cover, and simmer 5 minutes, stirring occasionally.
Add sugar, and bring to full rolling boil.
Boil 1 minute, stirring constantly.
Remove from heat, and add pectin.
Stir and skim 2 to 3 minutes.
Cool slightly, and ladle into 8 to10 sterilized jam or jelly glasses.
Seal at once with paraffin.
When cold, store in cool place.