WOOD-SORREL TRIBE 163 



Wood-sorrel (Oxdlis). — Sepals 5, united below ; petals 5, often 

 united below ; stamens united by the base of their filaments ; styles 5 ; 

 capsules 5-celled, angular. Name from the Greek oxijs, sharp or acid, from 

 the acid nature of the leaves. 



Wood-sorrel (OxcHis). 



1. Common Wood-sorrel (0. acetodlla). — Leaves all springing from 

 the root, ternate, hairy ; scape with 2 small bracts about the middle, single- 

 flowered ; root scaly. Perennial. There are few of our woodland flowers 

 more beautiful than this, when, in May, its clear triple leaf is spreading 

 around the trunks of the old trees. It might at first be taken for a mass 

 of clover, but the foliage is both thinner and of brighter green than that 

 of any of our species of trefoil, and the delicate white or lilac flower, veined 

 with purple, stands up gracefully from among it. As Linnseus remarked of 

 them, these pencilled bells close on the approach of rain; even when the 

 weather changes in a moment from sunshine to shower, though they were 

 before fully expanded, they are folded up immediately. The leaves are 

 always closed at night, as well as before and during rain. They are said 

 to shrink together, too, at a blow with a stick, and the seed-vessel partakes 

 of the general sensibility of the plant. This, if ever so slightly touched, 

 will open one of its valves, jerking out the seeds at the opening. "This," 

 says Mr. Curtis, " is not owing to any elasticity in the capsule itself, which 

 continues unchanged ; the cause of this propulsion is a strong, white, shining 

 arillus which covers the seed, and, bursting, by its elasticity throws the seed 

 to a distance." 



Many of the leaves of our common plants, especially such as are pinnate 

 in form, close regularly at night, as well as before rain. Anyone who 

 observes the foliage of a clover-field, or of the peas, vetches, or mountain-ash, 

 will see how readily they are affected by the moisture of the atmosphere, 

 or the approach of night. But we have not, in this country, any plant which 

 can at all compare with the sensitive plants, the Mimosas of tropical regions, 

 whose thousands of leaflets fold together at the slightest touch, so that the 

 Indians may well call them Dormideras, or sleepy plants. 



There are large tracts of country in hot and damp districts entirely 

 covered with Mimosce, where the vibration caused by the galloping of a' 

 horse past them is sufficient to set the whole mass in motion. We know 

 of no plant, however, truly wild in the British field or wood which would 

 better deserve the name of Sensitive Plant than our woodland Sorrel, 

 though the species termed Oxalis sfricfa, which can hardly be claimed as a 

 truly wild flower, has even more sensibility. The whole family of the Wood- 

 sorrels are remarkable in this respect. The leaves of the Oxalis sensitira are 

 well known to collapse on the slightest touch ; and Professor Morren, of 

 Liege, attributes to the Oxalis strida, which is naturalized in the counties 

 of Devon and Cornwall, the properties of the sensitive plants of the East. 

 The excitability and spontaneous movements of the leaves of this species, 

 which were accidentally observed by two of the pupils of this professor, in 

 the Botanic Garden of Modena, were communicated to the Royal Academy 

 at Brussels. Professor de Brognoli, in verifying some experiments which 



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