This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Ornamental North American shrubs, somewhat tender in places, and usually grown on warm walls. C. americanus - the New Jersey Tea plant - has clusters of white flowers; C. azureus has long dense racemes of pale-blue flowers in early summer. There are many varieties, the best being "Gloire de Versailles", with deep-blue flowers. One called "Albert Petit" has pinkish blossoms. C. Veitchianus is a fine Californian shrub with deep-blue flowers. All kinds are raised from seeds, cuttings of the ripened shoots, and by layers.