An expensive mass of blooms isn't necessary for a flower arrangement. The imaginative arrangement of even one flower or a single spray bearing several heads can be beautiful, according to Julia Clements, internationally recognized speaker, demonstrator and judge of floral art. She has received the highest award of the Royal Horticultural Society, the Victoria Medal of Honor.

Clements is the author of a new, beautifully illustrated book, "The Art of Arranging a Flower" (published by Walker and Co., 96 pages, $19.95). Through pictures and simple, easy-to-duplicate steps that even the uninitiated can follow, she makes it look easy.

"Always pick your flowers before they are fully mature. Try to pick them at night or early morning, when transpiration is at its lowest.

"Strip off the lower leaves, recut the stem ends under water to avoid an air-lock and leave for some hours in deep water in a dark place before arranging. This treatment will harden and fully charge the stems with water.

"All woody stemmed flowers such as lilac, viburnum, chrysanthemums, roses and other flowering shrubs should have some of the leaves removed and the stem ends split before they are placed in deep water. Add sugar, a teaspoonful to a pint.

"Leaves and sprays of greenery, especially the young leaves of spring-time should be submerged in a bath of water for some hours, even overnight, before being used.

"Some sugar in the water (one teaspoonful to a pint) will help strenthen them. This does not apply to the gray hairy 'woolly' leaves such as Stachys lantana and Onopordom thistle, for these soak up water like a sponge if submerged and hold it, turning the leaves more green.

"All of the above hints apply also to bought flowers from the florists."