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.
This genus has a few good plants, among the best being angustifolia, 1 ft., with pinkish and blue flowers; arvensis, deep blue and white; also officinalis, red turning to violet; saccharata, with spotted leaves and red flowers. They are all about 1 ft. high, and flower from March to July. Ordinary soil and shaded places are suitable, and they are increased by division and seeds.