Note: Information is dated. Do not rely on it.Plum. A stone fruit, widely grown in all temperate climates, and ranking third in importance among orchard products in the United States. The three principal types of plums are the European plums, Japanese, and native plums. The European plums thrive in the regions about the Great Lakes and northern states, and on the Pacific slope where the prune industry has reached its greatest development. The Japanese variety was introduced about 1870, and flourishes much farther south than the European plum. The native plum is inferior to either, though more hardy. The fruit is distinguished from the peach, its near relative, by its smooth skin and unwrinkedd stone. Firm, sweet-fleshed varieties of plums that can be successfully cured are called prunes. They are extensively grown on the Pacific slope where very favorable conditions exist for drying them.