A GARDENER'S WORLD; Gloriosa, the Eliza Doolittle of Daisies

IF I were starting a garden in an open, sunny spot, and if I wanted bright color quickly and a steady source of excellent cut flowers but lacked a big budget, there is no question what I would plant -gloriosa daisies. These short-lived perennials are properly named, for they are one of the glories of the garden from midsummer into fall.

Their care is simple. They germinate quickly from a package of seed sown either in early spring or in the fall, with fall slightly preferable for the earliest possible bloom the next year. Once established, they are reliable self-sowers, without making pests of themselves. And they can stand hot dry weather, which leaves many other flowers looking limp.

Gloriosa daisies are so diverse in color and form that they could almost make a garden all by themselves. I have several dozen clumps blooming in my front yard, and no two are exactly alike. Heights range from 15 to 30 inches. The blossoms vary in size from 2 to 6 inches across; most are single, but some are double or semi-double. The dominant color is deep gold, with a brown cone at the center, but there are also shades of russet and mahogany and copper, as well as some very appealing combinations.

When I consider the dazzling effect of a mass of gloriosas, as bright as the brass section of a symphony orchestra, I wonder why van Gogh ever bothered with sunflowers. But the answer is easy; he could not paint gloriosa daisies because there weren't any in his day. Introduced 31 years ago, they are younger than many gardeners who now grow them.

Seed catalogues seldom print histories of the seeds they offer, and that is a pity. Every plant has a history, sometimes a fascinating one, and knowing it gives gardening an extra dimension of pleasure. The story of the gloriosa daisy somewhat resembles the tale of Eliza Doolittle and her transformation by Prof. Henry Higgins, except that in this case the professor's name was Blakeslee.

Gloriosas owe their toughness and bright summer color to their ancestor, the black-eyed Susan (Rudbeckia hirta), the quintessentially American wildflower of roadsides and open fields. Native to the Midwestern states, this flower hitchhiked its way to the Eastern Seaboard in shipments of hay and clover in the 19th century, and quickly made itself at home.

Even in its natural state, the black-eyed Susan is worthy of a place in the garden, but it had a more glamorous future in store, thanks to Prof. Alfred Francis Blakeslee (1874-1954). Director of the Genetics Experiment Station at Smith College in Northampton, Mass., and the world's foremost expert on the datura, a genus of plants that includes Jimson-weed, Professor Blakeslee took the humble black-eyed Susan in hand in his later years.

Treating the seeds with the dangerous chemical colchicine, derived from the colchicum bulb, he set off to transform their genetic material. The seedlings usually died, but a few survived as tetraploids - plants with double the usual number of chromosomes. The extra chromosomes meant enlarged possibilities to produce new colors, new forms and also greater vigor through hybridization.

David Burpee, owner of the venerable seed company, W. Atlee Burpee, eventually acquired stock of the tetraploid black-eyed Susans and set his company to work improving them even further. Some 40 acres were given over to these plants. Superior ones were tagged for keeping, the rest discarded. Mr. Burpee gave explicit instructions to his workers to look for large flowers on fairly compact plants, for wide variations in color and for boldness of effect.

Mr. Burpee introduced these flowers commercially in 1957, to considerable fanfare. Hundreds of plants were forced into early bloom in greenhouses for display at the annual Philadelphia Flower Show in March, where they caused an enormous stir. Then he was interviewed on Edward R. Murrow's ''Person to Person'' television show, in which he sang the praises of his (and Professor Blakeslee's) gloriosa daisies.

Well launched, these splendid progeny of a common American wildflower have, ever since, been fine and trouble-free plants in many home gardens.