(see Encycl.), is a genus of plants, of which the most valuable species seems to be the Lichen Roccella, or Argol. As that species has not been noticed in the article referred to, the following account of it from Professor Beckmann will be acceptable to many of our readers:

It is found in abundance in some of the islands near the African coast, particularly in the Canaries, and in several of the islands in the Archipelago. It grows upright, partly in single, partly in double stems, which are about two inches in height. When it is old, these stems are crowned with a button sometimes round, and sometimes of a flat form, which Tournefort, very properly, compares to the excrescences on the arms of the fetus. Its colour is sometimes a light, and sometimes a dark grey. Of this moss, with lime, urine, and alkaline salts, is formed a dark red paste, which in commerce has the same name, and which is much used in dyeing. That well-known substance called lacmus is also made of it.

Theophrastus, Dioscorides, and their successor Pliny, give the name of Physos thalassion, or pontium, to this plant, which, notwithstanding its name, is not a weed but a moss; as it grew on the rocks of different islands, and particularly on those of Crete or Candia. It had, in their time, been long used for dyeing wool, and the colour it gave when fresh was so beautiful, that it excelled the ancient purple, which was not red, as many suppose, but violet. Pliny tells us, that with this moss dyers gave the ground or felt tints to those cloths which they intended to dye with the costly purple. When it was first employed as a dye by the moderns, is not so certain, though the Professor has proved, we think completely, that it must have been at least as early as the beginning of the 14th century.

"Among the oldest and principal Florentine families (says he), is that known under the name of the Oricellarii." Oricellarii or Rucellarii, Ruscclai or Ruccelai, several of whom have distinguished themselves as statesmen and men of letters. This family are descended from a German nobleman, named Ferro or Frederigo, who lived in the beginning of the twelfth century. One of his descendants, in the year 1300, carried on a great trade in the Levant, by which he acquired considerable riches, and returning at length to Florence, with his fortune, first made known in Europe the art of dyeing with argol. It is said, that a little before his return from the Levant, happening to make water on a rock covered with this moss, he observed, that the plant, which was there called respio, or respo, and in Spain orcella, acquired by the urine a purple, or, as others say, a red colour. He therefore tried several experiments; and when he had brought to perfection the art of dyeing wool with this plant, he made it known at Florence, where he alone practised it for a considerable time, to the great benefit of the state. From this useful invention, the family received the name of Oricellarii, from which, at last, was formed Ruccelai." The Professor, however, does not believe that this Florentine discovered the dye by means of the above-mentioned accident, but that he learned the art in the Levant, and on his return taught it to his countrymen.

"Our dyers do not purchase raw argol, but a paste made of it, which the French call orseille en pâte. The preparation of it was for a long time kept a secret by the Florentines. The person who, as far as I know, made it first known was Roletti; who, as he himself tells us, carried on the trade of dyer at Florence. Some information was afterwards published concerning it by Imperati* and Michelini the botanist†. In later times this art has been much practised in France, England, and Holland. Many druggists, instead of keeping this paste in a moist state with urine, as they ought, suffer it to dry, in order to save a little dirty work. It then has the appearance of a dark violet-coloured earth, with here and there some white spots in it.

"The Dutch (continues our author), who have found out better methods than other nations of manufacturing many commodities, so as to render them cheaper, and thereby to hurt the trade of their neighbours, are the inventors also of lacmus, a preparation of argol, called orseille en pierre, which has greatly lessened the use of that en pâte, as it is more easily transported and preserved, and fitter for use; and as it is besides, if not cheaper, at least not dearer. This art consists, undoubtedly, in mixing with that commodity some less valuable substance, which either improves or does not much impair its quality, and which, at the same time, increases its weight (A). Thus do they pound cinnamon and small finer than other nations, and yet sell both these articles cheaper. Thus do they sift cochineal, and sell it cheaper than what is unfiltered.

"It was for a long time believed, that the Dutch prepared their lacmus from those linen rags which in the south of France are dipped in the juice of the croton tinctorium; but at present, it is almost certainly known, that orseille en pâte is the principal ingredient in orseille en pierre that is in lacmus; and for this curious information we are indebted to Ferber. But whence arises the smell of the lacmus, which appears so like that of the Florentine iris?" Some of the latter may, perhaps, be mixed with it; for our author thinks, that he has observed in it small indissoluble particles, which may have been bits of the roots. The addition of this substance can be of no use to improve the dye; but it may increase the weight, and give the lack more body; and perhaps it may be employed to render imperceptible some unpleasant smell, for which purpose the roots of that plant are used on many other occasions.