"Help youself to a leaf," said my friend, as I admired the violet-blue flowers on arching stems of a plant in a sunny window. And so, I did take a leaf, and thus I was launched on growing Streptocarpus, the Cape Primrose. Since that time, I have grown Streptocarpus from seeds as well as from leaves and have had flowers of many shades of rose, red, purple and also white.

Streptocarpus is a fibrous-rooted member of the gesneriad family to which florist gloxinias and African violets belong. You can just smile at the people who say "it sounds like a disease" and explain that the name means twisted fruit, descriptive of the spirally twisted seed pod. The name is no more formidable than chrysanthemum, which we all pronounce without hesitation.

The plant with which I got my start was Constant Nymph, a hybrid developed from plants originally brougt to England from South Africa. Although its flowers are smaller than those of some of the earliest Streptocarpus hybrids, it was judged particularly desirable, and obviously having potential as a houseplant, because of its constant bloom.

Constant Nymph has clustered, wrinkled strap-shaped leaves. The flower-bearing stems arise on the leaf at its base. Several stems may grow from one leaf, each producing clusters of two to six flowers. These are deep violet-blue and funnel-shaped with yellow or whit throat. The blooming periods is from spring to fall, starting in April. With supplemental lighting it can be kept in bloom all year.

The care of Constant Nymph is simple. Flowers are produced in profusion when the plants are grown in strong light, but not direct sunlight. Insufficient light during the winter months will curtail floweing. In summer the plants can be grown outdoors in hanging baskets in light shade. Indoors under fluorescent lights for 14-16 hours per day they bloom year round.

A gritty potting mix is recommended. A soilless mix, such as Pro-Mix of Jiffy Mix, to which fine chicken grit is added gives the roots the needed aeration and drainaged. I add about a teaspoon of pulverized egg-shell per four-inch pot to raise the pH of the soil; a bit of ground limestone serves the same purpose.

Streptocarpus is not a heavy feeder. Fertilize every week with standard balanced (10-10-10) fertilizer diluted to one-fourth the recommended strength. When the plant is blooming, switch to a formula containing more phosporus, such as 12-36-14. My earliest experience, using Peters 15-30-15 only, feeding with every watering on plants grown under fluorescent lights, produced strong, flowering plants.

Regular, very dilute feedings at short intervals are more beneficial than concentrated doses at longer intervals - as is true with other houseplants.

Streptocarpus Constant Nymph forms a rosette fo leaves that grows directly out of the soil. For this reason, care in watering is important because of the danger of crown rot. Grow the plants rather dry. When you water, water thoroughly. Use tepid water. Never pour water into the crown of the plant. Do not let pots stand in water. Constant Nymph can revive even when slightly wilted. My experience has been that Streptocarpus species bloom best when slightly pot-bound: and when blooming they are thirsty.

The principal need of these plants is cool well-aerated roots. While Streptocarpus is a tropical plant, it comes from cool elevations; it grows best at relatively cool temperatures - 65 to 70 degrees F. A temperature as high as 85 may kill the plant and will certainly reduce flowering. Growing the plants on pebble trays insures needed humidity.

Low humidity or overfeeding may cause the leaves to brown, wilt, or curl under at the tips. Unsightly leaves can be trimmed to improved the plant's appearance while the cause is being corrected.

Because Constant Nymph is tolerant of our usual indoor growing conditions it has become a popular houseplant and nurserymen are producing it in quantity: it can now be found in many plant stores and garden centers.

Indoor gardening questions can be addresed to Jane Steffey in care of The Weekly, The Washington Post. 1150 15th St. Washington, D.C., 23071. Please include your name and telephone number.