on the approach of rain. The flower is regular; sepals five, petals five, stamens ten, stigmas five. The fruit is a five-angled, irritable capsule, from which the seeds are thrown with great force to a distance of several yards. In addition to the coloured spring flowers the Wood-Sorrel produces throughout the summer a large number of buds which never open (cleistogamous) but which develop into seed-vessels and discharge good seeds. The leaves have a pleasant acid flavour, due to the presence of oxalic acid. The generic name refers to this fact, and is derived from the Greek Oxys, sharp.
This is the only truly native species, but two others with yellow flowers have become naturalized in the S.W. of England. These are:
Procumbent Wood-sorrel (O. corniculata), with much-branched stalk; both stalk and branches soon becoming procumbent; and the flowers borne two or three on one peduncle. Leaves and stalks bronzed. Flowers June to September.
Upright Yellow Wood-sorrel (O. stricta) similar to the last, but with stem more erect; flowers two to eight on one peduncle.
The Wallflower (Cheiranthus cheiri).
This is not a British plant, though it has become firmly established on many old ruins throughout the country. It is a native of Central and Northern Europe, and according to Loudon was introduced to England in 1573. It is never found growing on rocks in this country, as would be the case were it a native. In some districts it is known as Gillyflower, a name corrupted from the French, Giroflée de Muraille. Old writers who use the name Gillyflower refer to the Clove Pink; in the present day the plant usually intended by the term is the Garden Stock. Culpepper calls this Winter Gillyflower. The wild plants are always the single yellow variety.
It is a Cruciferous plant, like the Bittercress and Shepherd's Purse, and the structure of the flowers is very similar to those. The sepals are very long, and for economy's sake that part of
