CLASS X. ORDER IV.] OXALIS. 659 



the leaflets of the plant before us is by no means a peculiarity; but as 

 it is a familiar example that may be observed by most persons, we 

 more particularly notice it as an illustration of some of the very in- 

 teresting investigations for the student in the economy of vegetable 

 life. Jn the leaf it is pretty well ascertained that the fluids of the 

 plant undergo the most important changes to their further elaboration, 

 not only for the perfection of the structure of the plant, but for the 

 perfect formation of its peculiar secretions; and to the accomplishment 

 of this end the action of light is one of the most important agents, 

 and, therefore, we see the leaflets during the day are fully exposed 

 to its influence; and by this movement another object is attained, 

 namely, the expanded leaflets prevent, by their projection forming a 

 covering over the roots, so great an evaporation of moisture as would 

 otherwise take place ; but during the night, when the heat of the day 

 is gone, and the dew begins to be deposited, the leaflets fall, that 

 the roots may be fully exposed to the influence of its deposition, to 

 the invigoralion of the plant, and supplying it with that moisture 

 which is evaporated from the leaves during the day. Thus far it may 

 be observed are some of the results consequent on the movement of the 

 leaflets ; but what the causes of this movement in the leaflets are we 

 must leave for the further investigation of the student : to slate the 

 imperfect knowledge which we possess of these causes would occupy 

 more space than we can here be allowed. 



Another result in consequence of these changes is readily ascer- 

 tained: on tasting the leaves, it will be found that the juices are 

 become of a pleasant acid flavour, which is from chemical investiga- 

 tions ascertained to be oxalic acid, in a state, according to Thomson, of 

 binoxalate of potash, and it is from the circumstance of this acid being 

 found in the leaves that it bears the name. Twenty pounds of the 

 leaves yield about six pounds of juice, which properly evaporated, &c., 

 gives two ounces and half of impure crystalizable salt, which, when 

 purified, forms flat semi-transparent crystals, having an intensely sour 

 taste and active poisonous properties, which, when taken internally in 

 the dose of half an ounce, prove rapidly fatal ; and even in the dose of 

 half a drachm they have been known to produce death after a few 

 days. Oxalic acid of the shops is not now prepared from the juice of 

 vegetables, since Scheele has discovered a method of procuring it by 

 acting upon sugar with nitric acid, and producing the salt by this 

 means more readily, and far more economically. Oxalic acid, when 

 mixed with cream of tartar, was sold under the name of salts of lemon, 

 and is useful in removing iron moulds, ink spots, and stains from linen, 

 as well as various other domestic purposes ; but since the real salts of 

 lemon, citric acid, is become so much cheaper, and at the same time 

 better, it has supplied its place. 



The leaves of the Wood-sorrel, notwithstanding the poisonous pro- 

 perties which they contain, are used in diff'erent parts of the Continent 

 as an ingredient in the spring salads, and form a delicate and very 



