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 pretty European rock plant, 6-9 in. high, with erect trusses of rich-violet flowers from June to September. There is a white variety, and one (Webbiana) with bright, rosy-purple blooms. They grow in ordinary garden soil, and are increased by division and seeds.