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.
A small genus of annual plants sometimes united with Campanula; but the corolla is rotate, filaments flat and hairy, and the capsule fusiform or prismatic. Speculum is the Latin equivalent of looking-glass, and is employed to designate these herbs on account of their bright corollas. S. hybrida is a small cornfield weed, bearing inconspicuous lilac-blue flowers.
S. speculum, syn. Prismatocdrpus. Venus's Looking-glass. - A slender branching plant about 6 or 8 inches high with linear leaves and reddish-violet, lilac, or white flowers about an inch in diameter. The calyx-lobes are linear, and exceed the corolla in length. A hardy little annual producing its pretty flowers in great profusion. It is a native of the South of Europe.