Fig. 129. Gyrophora polyrhiza Koerb. (S. H., Photo., reduced).
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.
Fig. 130. Lecanora esculenta Eversm. Loose nodules of the sterile thallus.
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.