tions depend upon the thallus being stratified or unstratified, and the apothecia open or closed. The unstratified Lichenales are termed, from Byssus, the normal genus, the Byssine; and of the stratified Lichens, those having open Apothecia, are denominated Cetrarina; those having closed Apothecia, Verrucarinæ ; from Cetraria and Verrucaria, the two normal genera of the respective groups. The types are distinguished by subordinate characters, hereafter to be explained.

(362.) Until lately, the system of arrangement devised by Acharius almost universally prevailed; but the distinction and distribution of these plants have been so much improved and simplified by Fries, that since the publication of his "Lichenographia Europea Reformata," no doubt can be entertained that his labours will form the foundation of all modern schemes: therefore, his method, with some few slight modifications to render it compatible with the principles of these Outlines, will be adopted here.

CETRARINE.

(363.) The Cetraria Islandica, formerly known as the Lichen Islandicus, or Iceland moss, is a familiar example of the most extensive and economically important section of the Lichenales. This section contains two well-marked types, and at least five subtypes, associated by having their " Apothecia open and disciferous;" these characters are common to them all, whence they have been sometimes termed the Gymnocarpi, or naked-fruited Lichens; but Cetrarina is perhaps a preferable name, not only from its being a derivative of a well-known normal genus, but also from its etymological reference to the open shield-like fructification that pervades and characterises the entire section.

(364.) Parmeliacea. Parmelia (the Shield-edge,*) and Usnea, (the Lichen-hair, or Beard-moss,)† are the normal genera of two subtypes, called, from them, the Usnida (or Usneæ,) and Parmelida (or Parmelieæ,) which, together, form the type Parmeliacea, the first that occurs in the section Cetrarinæ.

From racun, a little shield or target, and eiλew, to surround.

From the Arabic áchneh, the common name of all Lichens among the Arabians.

A. Usnea barbata. (a) Pendulous vertical thallus. (b) Open apothecia. B. Usnea barbata, var. articulata. (a) Barren ramifications. (6) Shields. c. Cetraria islandica. (a) subvertical thallus. (b) Apothecia. D. Cetraria juniperina. (a) Thallus. (b) Apothecium. E. Parmelia perforata. (a) Foliaceous thallus. (b) Open perforated apothecia. F. Parmelia parietina. Section of open apothecium.

(365.) The Usnide are distinguished by having an open disk, and being destitute of hypothallus. Their thalli, likewise, are vertical, either pendulous or erect, for in their evolution the centripetal force predominates.

The several varieties of Usnea, known commonly as Jupiter's beard (barba Jovis,) Tree-beard (Arborum barba,) &c. are, with some species of the two following genera, Evernia and Ramalina, the chief Lichens "which clothe so profusely the trees of too thick or decaying plantations; a fir wood on moorish ground is in particular much infested with them. The fir, the birch, the ash, the oak, the sloe, and the hawthorn are, when old, always hung with this hoary livery; but the elm, the sycamore, the lime, and the beech, wear it not, or very sparingly; so that when Gray speaks of the rude and moss-grown beech,' he applies to it a character by no means appropriate, for no tree is so little or so seldom either rude or moss-grown."-Johnson.

(366.) Evernia, a name admirably descriptive of the elegant branching thalli of the lichens to which it belongs, is derived from iv, excelling, and ovos, a branch. E. prunastri is one of the most common British species, and, from its peculiar power of imbibing and retaining odours, it is in much request as an ingredient in sweet pots and perfumed cushions; and Evelyn says, that this "very moss of the oak, that is white, composes the choicest cypress powder, which is esteemed good for the head; but impostors familiarly vend other mosses under that name, as they do the fungi for the true agaric, (excellent for hemorrhages and fluxes,) to the great scandal of physic."

One species of this genus, viz. Evernia vulpina, is said to be poisonous, at least to foxes; whence its name. It is curious that a deleterious plant should be found in such a generally innocuous group.

(367.) Lightfoot says that one species of Ramalina, the R. scopulorum, or rock-branchlet, (Lichen calicaris of Linneus, and L. scopulorum of Dickson,) "will dye a red colour, and promises, in that intention, to rival the famous L. roccella, or argol, which is brought from the Canary Islands, and sometimes sold at the price of £80. sterling per ton. It was formerly used, instead of starch, in hairpowder." Johnston adds to this account that another species, the R. farinacea, affords a mucilage as good as that obtained from the Cetraria islandica.

(368.) Roccella, a corruption of the Portuguese Roccha, is a name given to several species of lichen, in allusion to the situations in which they are found, delighting to grow on otherwise barren seaward rocks, that thus produce a profitable harvest. Tournefort considers that one species at least (R. tinctoria) was known to the ancients, and that it was the especial lichen (Aux) of Dioscorides, which was collected on the rocky islands of the Archipelago, from one of which it received the name of the "purple of Amorgus."

Both R. tinctoria and fuciformis are indigenous to Britain; they are found, though sparingly, on the maritime rocks of our southern coasts, especially in Portland Island; but in the Canary and Cape de Verd Islands, in Barbary, and the Levant, the former is common; and the latter, which "attains a much larger size, and is reported to vie in richness of colouring with the common orchill, is said to abound in the East Indies, especially on the shores of Sumatra;" and hence may probably become an important article of commerce.

(369.) Under the name of Archill, or Orchell, (the Orcella of the Italians, and the Orseille of the French,) large quantities of this lichen are annually imported into this country, varying from ninety tons and upwards per annum. In times of scarcity it has fetched as much as £1000. per ton, but its usual price is not above a fourth part of that sum. The Canary orchell sells now at double the price of the Madeira, and the Barbary is the least esteemed of all: the former being sold at £290. per ton, while the second and third are only worth £140. and from £30. to £45. respectively.

(370.) The ancient mode of preparing orchell is said to have been lost, and rediscovered casually by a Florentine merchant, in the year 1300; and its preparation was long kept a secret by the Florentines and the Dutch. The former, to lead other manufacturers astray, called it tincture of turnsole, pretending that it was extracted from the Heliotropium, or turnsole; and by the latter it was made into a paste, which they called lacmus, or litmus. At present it is well known that the process consists in cleaning, drying, and powdering the plant, which, when mixed with half its weight of pearlash, is moistened with human urine, and then allowed to ferment. The fermentation is kept up for some time by successive additions of urine, until the colour of the materials

changes to a purplish-red, and subsequently to a violet or blue. The principal British manufactories are in London and Liverpool. The colour of orchil is extremely fugitive, and it affords one of the most delicate chemical tests for the presence of an acid. The vapour of sulphuric acid has been thus detected, as pervading to some extent the atmosphere of London.

(371.) Cetraria [§ 364, fig. C, D,] from cetra, a Moorish buckler, is the modern systematic name of the genus that contains the Lichen islandicus, or Iceland moss, which in commerce is often mixed with another species, the C. odontella. Several species are natives of our alpine woods and mountainous heaths. Sir James E. Smith found the Islandica on the Pentland hills, on Ben Lomond, and in various parts of Scotland. It grows, however, much more freely in the more northern parts of Europe; and Dr. Holland states that it abounds on the lava on the western coast of Iceland, where the whole plant is much more luxuriant than with us.

The bitter and purgative principles of this Cetraria may be separated by steeping it in cold water, which is done by the Icelanders and other northern nations, with whom it forms an important article of food; these poor people with gratitude confessing that out of the rock the Almighty gives them food; commanding that the very stones should furnish bread.

(372.) Immense quantities of this lichen are annually collected in Iceland for exportation, as well as for home consumption. After steeping in cold water, drying, and powdering, the Icelanders make it into cakes, or eat it boiled in milk; and Henderson, in his Tour through Lapland, says that a porridge made of this lichen flour is to a foreigner not only the most wholesome, but also the most palatable, of all the articles of Icelandic diet.

The esculent qualities of the Iceland moss have been long recognised in many parts of the continent of Europe; and it has lately been recommended by authority to use it, either alone or mixed with flour, in the composition of bread in times of scarcity. The Saxon government have published a report on this subject, which is full of interesting information to the inhabitants of those mountainous districts where the plant abounds. In this report we are informed that 6 lbs. and 22 loths of lichen meal, boiled with 14 times its weight of water, and baked in this state with 591 lbs. of flour, produced 1114 lbs. of good household bread. Without this