Arnold Berry, age 9, of Vancouver, Wash., for his question:

HOW MANY KINDS OF PLUMS ARE THERE?

Botanists call the plum a drupe. It is a popular fruit that contains a stonelike seed.

It may surprise you to learn that there are more than 2,000 varieties of plums known. Only about 150 kinds, however, are important.

Most of the important varieties of plums fall into one of five classes: European, Japanese, American, damson and ornamental. Some are round while others are oval. Some are large while others are small.

Most of the plums that are dried as prunes are in the European class. European plums grow best in cool dry areas and do especially well in the northeastern Atlantic Coast states and on the Pacific Coast.

American plums grow best east of the Rocky Mountains while the Japanese varieties do well on the Pacific Coast.

Plums belong to the rose family, Rosaceae.