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 North American perennial, 1-2 ft. high, with ovate lance-shaped leaves and tubular purple-blue flowers from April to June, drooping from the axils of the upper leaves. Another good plant is sibirica, 1½ ft., with paler-blue flowers, which in the variety alba are white. M. echioides is a rare kind, 6 in. high, with rich-blue flowers; and closely related is primuloides, with deep gentian-blue flowers. Other kinds grown are ciliata, 2 ft., lanceolata, 1½ ft., and oblongifolia, 1 ft., all with blue flowers. Mertensias flourish in ordinary soil, and are raised from seeds sown in frames, and by division.