Jan Naismith, age 15, of Barre, Vt., for her question:

HOW ARE PLANTS CLASSIFIED?

There are over 300,000 different species of plants on earth. Since no two individual plants are exactly alike, the task of classifying them is not an easy one.

Closely related plants may be so much alike that it is very hard even for the experts to tell them apart. Plant classification takes long experience, good judgment and an eye for the form of plants.

The six chief areas of classification, from smallest to largest, are species, genus, family, order, class and phylum.

The scientific name of any plant always comes in two words. The first word is the name of the genus or group to which the plant belongs. The second name is the name of the species, or the particular kind within the group.

Here's an example: oaks belong to the genus Quercus, and all roses belong to the genus Rosa. But the white oak is Quercus alba and the red oak is Quercus rubra. Rosa alba is the white or York rose while Rosa centifolia is a cabbage rose.

In listing the names of several species within a group, the genus name may be abbreviated. Thus the red oak might be listed as Q. rubra.

The plural of genus is genera. Genera which are closely related, such as those of the roses (Rosa) and the genus to which apples belong (Malus), may be grouped together into a family. In the case of roses and apples, the genera are all grouped into the rose family, or Rosacea.

Closely related families of plants, such as the rose, bean and gooseberry families, can be combined and make up an "order" of plants. The three listed families belong to the Rosales order.

The rose, in turn, is included in the "class" called Angiospermae. This class includes all flowering plants.

Largest of the plant classification divisions i s the "phylum." Phylum of the rose and a number of plants from other classes is Tracheophyta. Members of this phylum all have tissues that carry material from one part of the plant to another.

The plural of phylum is phyla. There are 10 phyla of plants, which form two great subkingdoms. The submkingdom Tallophyta includes algae and fungi while the subkingdom Embryophyta include all other plants. It includes all plants that grow from embryos.

Latin names that do not change are used for plants by scientists. Sometimes they are difficult to remember when first read, but they make work much easier for persons who spend their lives in the study and classificaton of plants.

When botanists first began to name plants, Latin was the language of scholars everywhere. Today, often the species of a plant which i s listed i n Latin, i s also given a common name. The genus and species R. arkansana, for example, has the common name of Arkansas rose or prairie rose.