Some of the cookbooks praise different kinds of plums for making jelly. The British seem to favor green gages, and the French the mirabelle. And the beach plums of the North Atlantic seaboard make exceptional jelly. My first effort at making jelly was with a small, apricot-colored plum bought at a roadside stand near Santa Fe, but I never knew its name. It had a wonderfully spicy flavor, and I got all of two pints out of my haul. Do you have any favorite jelly or jam plums? Where do you usually get them?