This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
A charming Caucasian annual, 1-1½ ft. high, with masses of pure-white flowers borne on slender hair-like stems. Seeds are sown in the open air two or three times during the year in the shallow drills about 6 in. apart, chiefly to supply cut flower to the florists. G. viscosa is a soft rose-coloured form also grown. G. paniculata and its double-flowered variety are the best known of the perennial kinds. They have thick parsnip-like roots, and make dense bushes, 2-3 ft. high, smothered in small white flowers. Used for cut bloom in the same way as G. elegans, and may be increased by division in spring or autumn, or from seeds. Other kinds are G. cerastioides, 3 in., white, from the Himalayas, and G. repens, 4 in., rosy white.