THE WOOD SORRfiL. 12 



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 

 (cleistogamoiis\ but which develop into seed-vessels and dis- 

 charge 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, Giroflee 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. Cuipepper 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 



