The Potomac Unit of the Herb Society of America will hold its annual Herb Day on Thursday, May 14, 10 a.m. to 4 p.m., at the National Arboretum. The public is invited and admission is $2 -- a donation to the Arboretum.

Mrs. Edward Rea of the Herb Society will conduct a demonstration on constructing potpourri, an arrangement of dried petals set in a jar designed to release a pleasing fragrance into a room. Mrs. I. B. Richards will lecture on how herbs can be used in cooking, particularly as additives to butter and as replacements for salt.

there will be a tour of the Arboretum's recently opened National Herb Garden, demonstrations on the construction of herb wreaths and tussie mussies, and a sale of herb bread, plants and books on herbs.

Herbs not only offer an option to seasoning with salt, they can be used judiciously to completely eliminate salt from the diet if desired, according to specialists at Northrup King Co., Minneapolis, Minn. 55413, which offers 18 varieties of herbs in packet seeds to the consumer.

The flavor of fresh vegetables is greatly enhanced by herbs, rosemary adds an exciting touch to carrots, summer savory is perfect with snap beans and the treatment of sour cream with fresh-snipped chives for baked potatoes is unbeatable, they say.

Canned or frozen vegetables also come to life with a touch of the right herbs, especially if substituted for salt in the cooking liquid.

The National Arboretum plans to establish the world's finest research collection of flowering cherry trees, according to Dr. Frank S. Santamour, acting director of the Arboretum.

A comprehensive research collection of cherry trees is critical to the future existence of many of the world's 200-plus selections. Many cultivated varieties have already died out, victims or neglect and natural causes. Wild cherries, which have a significant potential for improving the disease resistance, hardness, and beauty of their cultivated cousins, are also being threatened by the accelerating loss of natural areas.

A decade from now there will be little point in attempting to collect flora from the wild, Santamour says. The wild in many countries will have disappeared.

This is true in Japan where the cultivation of sakura or garden cherry has been an honored art for 1,500 years. During World War II, many historic groves were cut for firewood and lumber. Japan's booming industrialization, with its attendant pollution and urbanization, has been only slightly kinder.

Yet the cherry's vulnerability brings hope for its preservation. In January, concerned Japanese officials came to the Science and Education Administration and the National Park Service seeking several thousand live cuttings of Washington's famed flowering cherry trees. The National Arboretum took cuttings from the Tidal Basin, Potomac Park, and Arboretum cherry collections. The majority of collected varieties had become extinct in Japan.

With Japanese-American horticultural cooperation, both countries will become the principal sources, East and West, for the genetic material of cherry and other members of the genus Prunus, Santamour says.

Ronald Jefferson, National Arboretum botanist, was in Japan during April to collect and identify as many wild and cultivated flowering cherries as he could find.

Cultivated and revered in Japan for centuries, the flowering cherry or sakura has suffered in the polluted and urbanized hands of modern society, says Santamour. Many varieties across the world face extinction. The National Arboretum itself harbors at least five varieties otherwise lost to the world.

Jefferson is equal to the formidable task of locating, documenting and helping to preserve the world's cherries, according to Santamour. During his 21 years of plant research he has performed similar feats for the world's flowering crabapples.

The Arboretum will eventually publish a comprehensive catalogue of the world's flowering cherries. Jefferson has already published a similar monograph on the history, progeny and location of the world's flowering crabapples.

Dr. Donald Egolf, National Arboretum research horticulturist, will head the breeding program for the cherries Jefferson collects. Uncommon and rare selections could prove particularly useful for improving genetic characteristics.

Developing superior resistance to many viral and bacterial blights will be a principal focus of the Arboretum's cherry research. Smaller, more shapely trees and increased beauty of blossom, leaf, and bark are also possible outcomes of such research.

"All of this, we believe, will add to the lasting beauty of many, many places," Santamour says.