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 good plant for the rockery or wall, with lance-shaped leaves and sulphur-yellow flowers. There is a form with variegated leaves. Other kinds are Marschalli, bright yellow; mutabilis, bronze purple; and kewensis, a cross between the Wallflower (see p. 118) and mutabilis. They flourish in good soil, and are raised from seeds, or cuttings only in the case of Marshalli.