Most people think of a terrarium as a landscape in a glass container. Whether it is a fish tank or a large glass or plastic sphere with plants skillfully and artistically arranged, a terrarium is a controlled environment, a contained atmosphere.

A single plant in the contained atmosphere of a bubble bowl is equally artistic, the same principles apply, and the making is not so fraught with anxiety as trying to provide for environmental needs of an assortment of plants.

An exceptionally good plant to grow in a bubble bowl by itself is the miniature, Begonia prismatocarpa, one of the few yellow-flowering begonias. This epiphytic begonia was discovered in 1861 growing on rocks and trees on a tropical island off the coast of West Africa, but it has only in recent years become widely known in the United States.

The main attribute of Begonia prismatocarpa is that it is almost ever-blooming. In addition, it is a small plant usable in a small container easily accommodated where space for plants is at a premium; it makes a delightful table piece in home or office.

This compact little plant has leaves one-half to one inch long - among the smallest among begonias. It grows to a height of only about 2 or 3 inches and its stems, or rhizomes, spread slowly to fill the container with glistering light green, hairy leaves. The abundance of yellow-orange flowers nestled among the leaves makes it an especially desirable plant to have, considering that we can't always count on having flowers in a contained atmostphere.

Begonia primatocarpa does need lots of light to bloom but not direct sunlight. If, instead of flowers, it is filling the bowl with leaves, it is not getting enough light. A fluorescent light garden is an ideal place to grow it, with the container 12 to 24 inches below the tubes.

Prepare to grow this little charmer by assembling your equipment. Select a small glass container - 6 or 8 inche bowl is a good size; it doesn't like a big bowl with detergent, rinse thoroughly, and dry it.

Place a half inch of perlite in the bottom of the bowl and sprinkle a layer of charcoal chips over it;this provides a drainage area for excess water.

Add moistened mix to a depth of one inch. Use a light powdery mix, half finely sifted peat moss and half perlite. Packaged terrarium mix of a light fluffy type may be used.

Then, plant the begonia and cover the container with a lid or with plastic wrap.

Condensation on the inside of covered containers indicates whether too much or too little moisture is present. If your begonia is obscured by the condensation, remove the cover to allow excess to be evaporate. This step may need to be repeated several times until there is only slight condensation - a thin film.

If there is no condensation on the sides of the bowl, the environment is too dry and you will need to add water.

Watering is a very important consideration with this bergonia. The growing mix will turn a lighter shade of brown as it dries. Because watering a container with no drainage is critical, it is best to use distilled water so that no waterbone chemicals are added. Tilt the container; point a baster to the sides of the bowl and let the water trickle into mix. Any water that is not absorbed by the mix within a few minutes should be drawn off with the baster. It is essential that there should never be an excess of water.

In the first, few weeks you should be watchful until you are sure that you have established the required moisture balance.

Begonia prismatocarpa is an excellent accent plant with other plants in a mixed planting, but it is most attractive as a single specimen in its own container.

In 1974, Michael Kartuz, well-known grower and hybridizer, introduced a hybrid between Begonia prismatocarpa and another epiphytic begonia, B. ficicola. The characteristics of both parents appear in the hybrid, which was named "Buttercup" because of its coin-dot yellow flowers.It, too, is plant for a contained atmosphere and has become a favorite of begonia hobbyists.

Both of these begonias are obtainable from the following mail order specialty nurseries: Kartuz Greenhouses, 92 Chestnut St., Wilmington, Ma., 01887; Logee's Greenhouses, 55 North St., Danielson, Ct., 06239.

One of the best ways of obtaining unusual and hard to find plants is to belong to a plant society. Begonia hobbyists have their own group, the Americanf Begonia Society. To obtain information about membership in the Potomac Branch, write to Maxine Zinman, Route 1, Box 73, Boyce, Va., 22620.