This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Perennial herbs with alternate unequally pinnate leaves and corymbose blue or white flowers. Calyx campanulate. Corolla rotate, 5-lobed. Stamens decimate, inserted on the throat of the corolla; filaments hairy at the base. Cells of the capsule many-seeded. There are about twelve species in temperate northern regions. The name is from war, but the application is not satisfactorily explained.
1. P. caeruleum (fig. 174). Jacob's Ladder, Greek Vale-rian. - An elegant border plant, and one of the oldest favourites in cottage gardens. Stems about 2 feet high, angular and fistular, and as well as the foliage glabrous or slightly pubescent, and glandular. Flowers white or blue, according to the variety, appearing in Summer. There is also a handsome variety with variegated foliage and white flowers.
Fig. 174. Polemonium caeruleum. (1/4 nat. size.)
A native of Central and Northern England and Europe, North Asia, and North America.
2. P. pulcherrimum. - A dwarfer less foliaceous species scarcely attaining a foot in height. Leaflets smaller, obtuse. Flowers bright blue, smaller, but more numerous than in the preceding. A native of North America, blooming in Summer.
P. reptans, humile, etc., are other North American species of dwarf spreading habit and blue or white flowers. The former is desirable on account of its early flowering season.