Lichens

J. A. Wheldon[1240] found the eggs of a species of mite, Tetranychus lapidus, attached to the fruits of Verrucaria calciseda, Lecidea immersa and L. Metzleri, calcicolous lichens of which the thallus not only burrows deep down into the limestone, but the fruits form in shallow excavated pits (Fig. 126). The eggs of this stone mite are found fairly frequently on exposed limestone rocks, bare of vegetation, except for a few crustaceous lichens. “There is usually a single egg, rarely two, in each pit apparently attached to the old lichen apothecium. The eggs are very attractive objects under a lens; they measure ·5 mm. in diameter, and are disc-like with a central circular depression from which numerous ridges radiate to the circumference, like the spokes of a wheel. When fresh, they have a white pearly lustre, becoming chalk-white when dry and old.” Wheldon’s observations were made in the Carnforth and Silverdale district of West Lancashire.

A minute organism, Hymenobolina parasitica[1241], first described by Zukal and doubtfully grouped among the mycetozoa, feeds, in the plasmodium stage, on living lichens. The parasitic habit is unlike that of true mycetozoa. It has recently been recorded from Aberdeenshire.

b. Insect mimicry of Lichens. Paulson and Thompson[1242] give instances of moth caterpillars, which not only feed on lichens, but which take on the coloration of the lichens they affect, either in the larval or in the perfect moth stage. “One of the most remarkable examples of this protective resemblance to lichens is that of the larva of the geometrid moth, Cleora lichenaria, which feeds upon foliose lichens growing upon tree-trunks and palings, and being of a green-grey hue, and possessed of two little humps on many of their body-segments, they so exactly resemble the lichens in colour and appearance as to be extremely difficult of detection.” Several instances are recorded of moths that resemble the lichens on which they settle: perfect examples of such similarity are exhibited at the Natural History Museum, South Kensington, where Teras literana, Moma orion, and other moths are shown at rest on lichen-covered bark from which they can hardly be distinguished.

Another curious instance of suggested mimicry is recorded by G.E. Stone[1243]. He spotted a number of bodies on the bark of some sickly elms in Massachusetts. They were about 1/8 of an inch in diameter “with a dark centre and a drab foliaceous margin.” They were principally lodged in the crevices of the bark and Stone collected them under the impression that they were the apothecia of a lichen most nearly resembling those of Physcia hypoleuca. Some of the bodies were even attached to the thallus of a species of Physcia; others were on the naked bark and had every appearance of lichen fruits. Only closer examination proved their insect nature, and they were identified as belonging to a species Gossypina Ulmi, an elm-leaf beetle common in Europe where it causes a disease of the tree. It had been imported into the United States and had attacked American elms.

It is stated by Tutt[1244] that the larvae of many of the Psychides (Lepidoptera) live on the lichens of trees and walls, such as Candelaria concolor, Xanthoria parietina, Physcia pulverulenta and Buellia canescens, and that their larvae pupate on their feeding grounds. Each species makes a “case” peculiar to itself, but those of the lower families are usually covered externally with grains of sand, scraps of lichens, etc. The “case” of Narcyria monilifera, for instance, is somewhat raised on a flat base and is obscured with particles of sand and yellow lichen, giving the whole a yellow appearance. That of Luffia lapidella is roughly conical and is held up at an angle of 30° to 45° when the larva moves. The “cases” of Bacotia sepium are always upright; they measure about 5·5 mm. in height and 2·75 mm. in width and present a hoary appearance from the minute particles of lichen with which they are covered, so that the structure is not unlike the podetium of a Cladonia.

c. Food for the Higher Animals. It has been affirmed, especially by Henneguy, that many lichens, if deprived of the bitter principle they contain, by soaking in water, or with the addition of sodium or potassium carbonate, might be used with advantage as fodder for animals. He cites as examples of such, Lobaria pulmonaria, Evernia prunastri, Ramalina fraxinea, R. farinacea, and R. fastigiata, all of which grow abundantly on trees, and owe their nutritive quality to the presence of lichenin, a carbohydrate allied to starch.

Cladonia rangiferina (Fig. 127), the well-known “reindeer moss,” is, however, the lichen of most economic importance, as food for reindeer, cattle, etc. It is a social plant and forms dense tufts and swards of slender, much branched, hollow stalks of a greenish-grey colour which may reach a height of twelve inches or even more; the stalks decay slowly at the base as they increase at the apex, so that very great length is never attained. In normal conditions they neither wither nor die, and growth continues indefinitely. It is comparatively rare in the northern or hilly regions of the British Isles, and is frequently confused with the somewhat smaller species Cl. sylvatica which is very common on our moorlands, a species which Zopf[1245] tells us reindeer absolutely refuse to eat.

The true reindeer moss is abundant in northern countries, more especially in forest regions[1246] and in valleys between the tundra hills which are more or less sheltered from the high winds; it is independent of the substratum and flourishes equally on barren sand and on wet turf; but grows especially well on soil devastated by fire. For long periods it may be covered with snow without injury and the reindeer are accustomed to dig down with horns and hoofs in order to reach their favourite food. Though always considered as peculiarly “reindeer” moss, deer, roebuck and other wild animals, such as Lemming rats[1247], feed on it largely during the winter. In some northern districts it is collected and stored as fodder for domestic cattle; hot water is poured over it and it is then mixed with straw and sprinkled with a little salt. Johnson[1248] has reported that the richness of the milk yielded by the small cows of Northern Scandinavia is attributed by some to their feeding in great measure on the “reindeer moss.”

When Cladonia rangiferina is scarce, a few other lichens[1249] are made use of, Alectoria jubata, a brownish-black filamentous tree-lichen being one of the most frequent substitutes. Stereocaulon paschale, which grows in large dense tufts on the ground in mountainous regions, is also eaten by reindeer and other animals; and Iceland moss, Cetraria islandica, is stored up in large quantities by the Icelanders and used as fodder. Willemet[1250] reports it as good for horses, oxen, cows and pigs.

It is interesting to recall a discovery of prehistoric remains at the Abbey of Schussenried on the Lake of Constance and described by F. Keller[1251]: under successive beds of peat and crumbly tufa, there was found a layer, 3 feet thick, containing flints, horns of reindeer and bones of various animals, and, along with these, masses of reindeer moss; a sufficient proof of its antiquity as a fodder-plant.

d. Food for Man. Lichens contain no true starch nor cellulose, but the lichenin present in the cell-walls of the hyphae has long been utilized as a food substance. It is peculiarly abundant in Cetraria islandica (Fig. 128), which grows in northern countries, covering great stretches of ground with its upright strap-shaped branching fronds of varying shades of brown. In more southern lands it is to be found on high hills or on upland moors, but in much smaller quantities. Commercial “Iceland moss” is supplied from Sweden, Norway or Iceland. In the last-named country the inhabitants harvest the lichen preferably from bare stony soil where there is no admixture of other vegetation. They revisit the locality at intervals of three years, the time required for the lichen to grow to a profitable size; and they select the wet season for the ingathering of the plants as they are more easily detached when they are wet. If the weather should be dry, they collect it during the night. When gathered it is cleansed from foreign matter and washed in water to remove as much as possible of the bitter principle. It is then dried and reduced to powder. When required, the powder is put to macerate in water for 24 hours, or it is soaked in a weak solution of soda or of carbonate of potassium, by which means the bitter cetraric acid is nearly all eliminated. When boiled[1252] it yields a jelly which forms the basis of various light and easily digested soups or of other delicacies prepared by boiling in milk, which have been proved to be valuable for dyspeptics or sufferers from chest diseases. The northern nations also make the powder into bread, porridge or gruel. Johnson[1253] states in his account of “Useful Plants” that considerable quantities of Iceland moss were formerly employed in the manufacture of sea biscuit, and that ship’s bread mixed with it was said to be less liable to the attacks of weevil than when made from wheat flour only.

An examination of the real food value of the mucilaginous extract from “Iceland moss” has been made by several workers. Church[1254] states that for one part of flesh formers, there are eight parts of heat-givers reckoned as starch. Brown[1255] isolated the two carbohydrates, lichenin and isolichenin. The former, a jelly which yields on hydrolysis a large quantity of a reducing sugar, dextrose, ferments with yeast and gives no phloroglucin reaction; it is unaffected by digestion and probably does not form glycogen. Iso-lichenin is much less abundant and resembles soluble starch, but on digestion yields only dextrins—no sugar. It may be concluded, judging from the chemical nature of the mucilage, from the resistance of its constituents to digestion and from the small amount present in the jelly, that its nutritive value is practically nil[1256].

It has been stated that “reindeer moss” in times of food scarcity is powdered and mixed with “Iceland moss” and rye to make bread in North Finland. Johnson confirms this and cites the evidence of a Dr Clarke that: “to our surprise we found we might eat of it with as much ease as of the heart of a fine lettuce. It tasted like wheat-bran, but after swallowing it, there remained in the throat and upon the palate a gentle heat, or sense of burning, as if a small quantity of pepper had been mixed with the lichen.”

The Egyptians[1257] have used Evernia prunastri, more rarely E. furfuracea, in baking. In the eighteenth century fermentative agents such as yeast were unknown to them, and these lichens, which were imported from more northern lands, were soaked in water for two hours and the solution then mixed with the flour to give a much appreciated flavour to the unleavened bread.

In India[1258] a species of Parmelia (near to P. perlata) known in the Telegu language as “rathapu” or rock-flower has been used as a food, generally prepared as a curry, by the natives in the Bellary district (Madras Presidency), and is esteemed as a delicacy. It is also used medicinally. The collecting of rathapu is carried on during the hot weather in April and May, and forms a profitable business.

A note has been published by Calkins[1259], on the authority of a correspondent in Japan, that large quantities of Endocarpon (Dermatocarpon) miniatum (Fig. 56) are collected in the mountains of that country for culinary purposes, and largely exported to China as an article of luxury. The local name is “iwataka,” meaning stone-mushroom. Properly prepared it resembles tripe. It is possibly the same lichen under a different name, Gyrophora esculenta, which is described by Manabu Miyoshi[1260] as of great food value in Japan where it is known as “iwatake.” It is a greyish-brown leathery “monophyllous” plant of somewhat circular outline and fairly large size, measuring 3 to 13 cm. across. Fertile specimens are rare, and are smaller than the sterile. It grows generally on the steep declivities of damp granitic rocks and is common in various districts of Japan, being especially abundant on such mountains as Kiso, Nikko, Kimano, etc. The face of the precipices is often thickly covered with the lichen growth. The inhabitants collect the plants in large quantities. They dry them and send them to the towns, where they are sold in all vegetable stores; some are even exported to other countries. These lichens are not bitter to the taste, nor are they irritating as are other species of the genus. They are on the contrary quite harmless and are much relished by the Japanese on account of their agreeable flavour, in spite of their being somewhat indigestible. Though only determined scientifically in recent times, this edible lichen has long been known, and the risks attending its collection have frequently been described in Old Chinese and Japanese writings.

Other species of Gyrophora including G. polyrhiza (Fig. 129) and Umbilicaria, black leathery lichens which grow on rocks in northern regions, have also been used as food. They are the “Tripe de Roche” or Rock Tripe of Arctic regions, a name given to the plants by Canadian fur-hunters. They have been eaten by travellers and others in desperate straits for food; but though to a certain extent nutritious, they are bitter and nauseous, and cause severe internal irritation if the bitter acids are not first extracted by boiling or soaking.

Of more historical interest is the desert lichen Lecanora esculenta, supposed to be the manna[1261] of the Israelites, and still called “bread from heaven.” Eversmann[1262] wrote an account of its occurrence and qualities, and fuller information was given by Berkeley[1263]: when mixed with meal to a third of its weight it is made into bread and eaten by the desert tribes. It grows abundantly in North Africa and in many parts of Western Asia, on the rocks or on soil. It is easily broken off and driven into heaps by the wind; and has been reported as covering the soil to a depth of 15 cm. to 20 cm. with irregular contorted lumps varying in size from a pea to a small nut (Fig. 130). Externally these are clear brown or whitish; the interior is white, and consists of branching interlaced hyphae, with masses of calcium oxalate crystals, averaging about 60 per cent. or more of the whole substance.

A still more exhaustive account is given by Visiani[1264], who quotes the experience of a certain General Jussuf, who had tested its value in the Sahara as food for his soldiers. When bread was made from the lichen alone it was friable and without consistency; when mixed with a tenth portion of meal it was similar to the soldiers’ ordinary bread, and had something of the same taste. The General also gave it as fodder to the horses, some of them being nourished with the lichen and a mixture of barley for three weeks without showing any ill effects. It is also said that camels, gazelles and other quadrupeds eat it with advantage, though it is in any case a very defective food.

A remarkable deposit of the lichen occurred in recent times in Mesopotamia during a violent storm of hail. After the hail had melted, the ground was seen to be covered, and specimens were sent to Errera[1265] for examination. He identified it as Lecanora esculenta. In his opinion two kinds of manna are alluded to in the Bible: in one case (Exodus xvi.) it is the sweet gum exuded from the tamarisk that is described; the other kind (Numbers xi.), he thinks, plainly refers to the lichen. He considers that its nutritive value must be very low, and it can only be valued as food in times of famine.

B. Lichens as Medicine

a. Ancient Remedies. An interesting note has been published by Müller-Argau[1266] which seems to trace back the medicinal use of lichens to a very remote age. He tells us that Dr Schweinfurth, the distinguished traveller, who made a journey through the valley of the Nile in 1864, sent to him from Cairo a piece of lichen thallus found in a vase along with berries of Juniperus excelsa and of Sapindus, with some other undetermined seeds. The vase dated from the 18th Dynasty (1700 to 1600 B.C.), and the plants contained in it must thus have lain undisturbed over 3000 years. The broken pieces of the lichen thallus were fairly well preserved; they were extremely soft and yellowish-white and almost entirely decorticate, but on the under surfaces there remained a few black patches, which, on microscopical examination, enabled Müller to identify them as scraps of Evernia furfuracea. This lichen does not grow in Egypt, but it is still sold there along with Cetraria islandica and some other lichens as foreign drugs. Dr Schweinfurth considered his discovery important as proving the use of foreign remedies by the ancient Egyptians.

b. Doctrine of “Signatures.” In the fifteenth century A.D. there was in the study and treatment of disease a constant attempt to follow the guidance of nature. It was believed that Providence had scattered here and there on plants “signatures,” or resemblances more or less vague to parts of the human body, or to the diseases to which man is subject, thus indicating the appropriate specific.

Lichens among other plants in which any “signature” could be detected or imagined were therefore constantly prescribed: the long filaments of Usnea barbata were used to strengthen the hair; Lobaria pulmonaria, the true lung-wort, with its pitted reticulate surface (Fig. 72), was marked as a suitable remedy for lung troubles; Xanthoria parietina being a yellow lichen was supposed to cure jaundice, and Peltigera aphthosa, the thallus of which is dotted with small wart-like tubercles[1267], was recommended for children who suffered from the “thrush” eruption.

The doctrine reached the height of absurdity in the extravagant value set on a lichen found growing on human skulls, “Muscus cranii humani” or “Muscus ex cranio humano.” There are a number of lichens that grow indifferently on a variety of substances, and not infrequently on bones lying in the open. This skull lichen[1268], Parmelia saxatilis (Fig. 131) or some other, was supposed to be worth its weight in gold as a cure for epilepsy. Parkinson[1269] tells us in all confidence “it groweth upon the bare scalps of men and women that have lyen long ... in former times much accounted of because it is rare and hardly gotten, but in our own times much more set by, to make the ‘Unguentum Sympatheticum’ which cureth wounds without the local application of salves ... but as Crollius hath it, it should be taken from the sculls of those that have been hanged or executed for offences.” Ray[1270] says that the same gruesome plant “is celebrated by several authors as useful in haemorrhages and is said to be an ingredient of the famous ‘Unguentum Armarium[1271],’ reported to have been invented by Paracelsus.” Another lost ointment!

c. Cure for Hydrophobia. Still another lichen to which extraordinary virtue was ascribed, was the very common ground species Peltigera canina (Fig. 54), a preparation of which was used in the cure of rabies. Dillenius[1272] has published in full the prescription as “A certain Cure for the Bite of a Mad Dog” which was given to him by a very celebrated physician of that day, Dr Richard Mead, who had found it effective:

“Let the patient be blooded at the arm, nine or ten ounces. Take of the herb called in Latin Lichen cinereus terrestris, in English Ash-coloured ground liverwort, clean’d, dry’d and powder’d half an ounce. Of black pepper powder’d two drachms.

“Mix these well together and divide the Powder into four Doses, one of which must be taken every Morning, fasting, for four Mornings successively in half a Pint of Cow’s Milk warm. After these four Doses are taken, the Patient must go into the cold bath, or a cold Spring or River, every Morning fasting, for a Month. He must be dipt all over but not stay in (with his head above water) longer than half a minute, if the Water be very cold. After this he must go in three Times a Week for a Fortnight longer.”

Lightfoot[1273], some forty years later, refers to this medicine as “the once celebrated ‘Pulvis antilyssus,’ much recommended by the great Dr Mead.” He adds that “it is much to be lamented that the success of this medicine has not always answered the expectation. There are instances where the application has not prevented the Hydrophobia, and it is very uncertain whether it has been at all instrumental in keeping off that disorder.” Belief in the efficacy of the powder died out before the end of the century but the echo of the famous remedy remains in the name Peltigera canina, the dog lichen.

d. Popular Remedies. Lichens with very few exceptions are non-poisonous plants. They owed their repute as curative herbs to the presence in the thallus of lichenin and of some bitter or astringent substances, which, in various ailments, proved of real service to the patient, though they have now been discarded in favour of more effective drugs. Some of them, on account of their bitter taste, were frequently used as tonics to replace quinine in attacks of fever. Several species of Pertusaria, such as the bitter P. amara (Fig. 132), and of Cladonia as well as Cetraria islandica (Fig. 128), were recommended in cases of intermittent fever; species of Usnea and others, as for instance Evernia furfuracea, were used as astringents in haemorrhages; others were given for coughs, Cladonia pyxidata (Fig. 69) being supposed to be specially valuable in whooping cough.

One of the most frequently prescribed lichens was the tree lung-wort (Lobaria pulmonaria) (Fig. 72). It was first included among medical plants by Dorstenius[1274], a Professor at Marburg; he gives a good figure and supplies directions for its preparation as a cure for chest complaints. The doctrine of “signatures” influenced practitioners in its favour, but it contains lichenin which acts as an emollient. In England, it was taken up by the famous Dr Culpepper[1275], who, however, believed in astrology even more than in signatures. He says: “it is of great use with many physicians to help the diseases of the lungs and for coughs, wheesings and shortness of breath which it cureth both in man and beast.” He adds that “Jupiter seems to own the herb.” A century later we find Dr John Hill[1276], who was a physician as well as a naturalist, stating that the great tree lung-wort has been at all times famous in diseases of the breast and lungs, but by that time “it was not much used owing to change in fashions.”

The only lichen that has stood the test of time and experience as a real remedy is Cetraria islandica, and even the “Iceland moss” is now rarely prescribed. The first mention in literature of this famous plant occurs in Cordus[1277] as the Muscus with crisp leaves. Some years later it figures among the medicinal plants in Sibbald’s[1278] Chronicle of the Scottish Flora, and Ray[1279] wrote of it about the same time as being known for its curative and alimentary properties. It was Linnaeus[1280], and later Scopoli[1281], who gave it the important place it held so long in medicine. It has been used with advantage in many chronic affections as an emollient and tonic. Cramer[1282] in a lengthy dissertation gathered together the facts pertaining to its use as a food, a medicine and for dyeing, and he gives recipes he had himself prescribed with marked success in many different maladies. It has been said that if “Iceland moss” accomplished all the good it was alleged to do, it was indeed a “Divine gift to man.”

The physiological action of cetrarin (acid principle of the lichen) on living creatures has been studied by Kobert[1283] and his pupils. It has not any poisonous effect when injected into the blood, nor does it work any harm when taken into the stomach even of small animals, so that it may be safely given to the most delicate patients. Nearly always after small doses peristaltic movements in the intestines are induced which indicate that as a drug it might be of service in the case of enfeebled organs. In larger doses it may cause collapse in animals, but if administered as free cetraric acid it passes through the stomach unchanged to become slowly and completely dissolved in the intestine. The mucous membrane of the intestine of animals that had been treated with an overdose, was found to be richer in blood so that it seems as if cetrarin might be of service in chlorosis and in assisting digestion.

Cetrarin has also been proved to be a nerve excitant which might be used with advantage in mental maladies.

C. Lichens as Poisons

Though the acid substances of lichens are most of them extremely irritating when taken internally, very few lichens are poisonous. Keegan[1284] writing on this subject considers this quality of comparative innocuousness as a distinctive difference between fungi and lichens and he decides that it proves the latter to be higher organisms from a physiological point of view: “the colouring matters being true products of deassimilation, whereas those of fungi are decomposition or degradation waste products of the albuminoids akin to alkaloids.”

The two outstanding exceptions to this general statement are the two Alpine species Letharia vulpina and Cetraria pinastri. The former contains vulpinic acid in the cortical cells, the crystals of which are lemon-yellow in the mass. Cetraria pinastri produces pinastrinic acid in the hyphae of the medulla and the crystals are a beautiful orange or golden yellow.

These lichens, more especially Letharia vulpina, have been used by Northern peoples to poison wolves. Dead carcasses are stuffed with a mixture of lichen and powdered glass and exposed in the haunts of wolves in time of frost. Henneguy[1285], who insists on the non-poisonous character of all lichens, asserts that the broken glass is the fatal ingredient in the mixture, but Kobert[1286], who has proved the poisonous nature of vulpinic acid, says that the wounds caused by the glass render the internal organs extremely sensitive to the action of the lichen.

Kobert, Neubert[1287] and others have recorded the results of experiments on living animals with these poisons. They find that Letharia vulpina either powdered or in solution has an exciting effect on the mucous membrane. Elementary organisms treated with a solution of the lichen succumbed more quickly than in a solution of the acid as a salt. Kobert concluded that vulpinic acid is a poison of protoplasm.

He further tested the effect of the poison on both cold- and warm-blooded animals. Administered as a sodium salt, 4 mg. proved fatal to frogs. The effect on warm-blooded animals was similar. A sodium salt, whether swallowed or administered as subcutaneous or intravenous injections, was poisonous. Cats were the most sensitive—hedgehogs the least—of all the animals that were subjected to the experiments. Volkard’s[1288] synthetic preparation of vulpinic acid gave the same results as the solution directly extracted from the lichens.

D. Lichens used in Tanning, Brewing and Distilling

The astringent property in Cetraria islandica and in Lobaria pulmonaria has been made use of in tanning leather. The latter lichen grows commonly on oak and could hardly be gathered in sufficient quantity to be of commercial importance. Like many other lichens it develops very slowly. Lobaria pulmonaria has also been used to replace hops in the brewing of beer. Gmelin[1289] in his journey through Siberia visited a monastery at Ussolka where the monks employed it for this purpose. The beer tasted exactly like that made with hops, but was more intoxicating. The lichen in that country grew on pine-trees.

Lichens have in more modern times been used in the preparation of alcohol. The process of manufacture was discovered by Roy of Tonnerre, early in the nineteenth century, and was described by Léorier[1290]. It was further improved by Stenberg[1291], a Professor of Chemistry in Stockholm. Roy had worked with Physcia ciliaris, Ramalina fraxinea, R. fastigiata, R. farinacea and Usnea florida, but Stenberg and distillers after his time[1292] made more use of Cladonia rangiferina (Fig. 127), Cetraria islandica (Fig. 128) and Alectoria jubata.

By treatment with weak sulphuric or nitric acid the lichenin of the thallus is transformed into glucose which on fermentation forms alcohol. Stenberg found that 68 per cent. of the weight in Cladonia rangiferina was a “sugar” from which a good brandy could be prepared: a kilogramme of the lichens furnished half a litre of alcohol. The Professor followed up his researches by establishing a distillery near Stockholm. His papers contain full instructions as to collecting and preparing the plants. Henneguy[1293], writing in 1883, stated that the fabrication of alcohol from lichens was then a large and increasing industry in Sweden. The whole industry seems, however, to have fallen into disuse very soon: Wainio[1294], quoting Hellbom[1295], states that the various distilleries were already closed in 1884, because of the exhaustion of the lichen in the neighbourhood, and the impossibility of obtaining sufficient supplies of such slow-growing plants.

E. Dyeing Properties of Lichens

a. Lichens as Dye-plants. Knowledge as to the dyeing properties of lichens dates back to a remote antiquity. It has been generally accepted that lichen-colours are indicated by the prophet Ezekiel in his denunciation of Tyre: “blue and purple from the Isles of Elishah was that which covered thee.” Theophrastus describes certain plants as growing in Crete, and being used to dye wool, etc., and Pliny in his Phycos Thalassion is also understood as referring to the lichen Roccella, “with crisp leaves, used in Crete for dyeing garments.”

Information as to the dyeing properties of certain lichens is given in most of the books or papers dealing with these plants from the herbals onwards. Hoffmann[1296] devoted a large part of his Commentatio de vario Lichenum usu to the dye-lichens, and, illustrating his work, are a series of small rectangular coloured blocks representing samples of woollen cloth dyed with different lichens. There are seventy-seven of these samples with the colour names used by French dyers.

An important treatise on the subject translated into French was also contributed by Westring[1297]. He desired to draw attention to the tinctorial properties of lichens other than the Roccellae which do not grow in Sweden. The Swedes, he states, already used four to six lichens as dye-plants, but only for one colour. He demonstrated by his improved methods that other colours and of finer tint could be obtained. He describes the best methods both of extraction and of dyeing, and then follows with an account of the different lichens likely to be of service. The treatise was subsequently published at greater length in Swedish[1298] with twenty-four very fine coloured illustrations of the lichens used, and with sample blocks of the colours to be obtained.

b. The Orchil Lichen, Roccella. The value of Roccella as a dye-plant had been lost sight of until it was accidentally rediscovered, early in the fourteenth century, by a Florentine merchant called Federigo. He introduced its use into Florence, and as he retained the industry in his own hands he made a large fortune, and founded the family of the Orcellarii, called later the Rucellarii or Rucellai, hence the botanical name, Roccella. The product was called orseille for which the English name is orchil or archil. Another origin suggested for orchil is the Spanish name of the plant, Orcigilia. There are a number of different species that vary in the amount of dye-product. Most of them grow on rocks by the sea-side in crowded bluish-grey or whitish tufts of strap-shaped or rounded stiff narrow fronds varying in length up to about six inches or more. The main supply of “weeds” came from the Levant until the fifteenth century when supplies were obtained from the Canaries (long considered to produce the best varieties), Cape Verd and the African coasts. The geographical distribution of the Roccellae is very wide: they grow on warm sea-coasts all over the globe, more particularly in Angola, the Cape, Mozambique, Madagascar, in Asia, in Australia, and in Chili and Peru.

Zopf[1299] has proved the existence of two different colouring substances among the Roccellas: in R. fuciformis (Fig. 57) and R. fucoides (both British species), in R. Montagnei and R. peruensis the acid present is erythrin; in R. tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In R. tinctoria (Fig. 133), according to Ronceray[1300], the acid is located chiefly in the gonidial layer and the soredia but is absent from the cortex and centre. In R. portentosa it is abundant in the cortex and central layer, while scarcely to be detected in the gonidial layer, and it is wanting altogether in the soredia. In R. Montagnei it is chiefly found in the cortex and the gonidial layer, and is absent from the soredia and from the medulla.

c. Purple Dyes: Orchil, Cudbear and Litmus. Orseille or orchil is formed not only from erythrin and lecanoric acid (orseillic acid), but also from erythrinic, gyrophoric, evernic and ramalic acids[1301] and may be obtained from any lichen containing these substances. By the action of ammonia the acids are split up into orcin and carbonic acid. In time, under the influence of ammonia and the oxygen of the air[1302], orcin becomes orcein which is the colouring principle of orchil; the perfecting of the process may take a month. The dye is used for animal fibres such as wool and silk; it has no effect on cotton.

There are several different preparations on the market, chiefly obtained from France and Holland; orchil or orseille in the form of a solution, cudbear (persio of Germany) almost the same, but manufactured into a violet-reddish powder, and litmus (tournesol of France) which is prepared in a slightly different manner. At one time the lichen, broken into small pieces, was soaked in urine; a fermentation process was set up, then lime and potash with an admixture of alum were added. The mass of material when ready was pressed into cubes and dried in the air. Commercial litmus contains three substances, erythrolein, erythrolitmin and azolitmin; the last named, which is the true litmus, is a dark brown amorphous powder soluble in water, and forming a blue solution with alkalies.