The relations of the Alga and the Fungus, which have formed a close associationship in the structure known as the Lichen, were established many years ago.
Schimper distinguishes moss tundra, Pot ytrichum tundra, and lichen tundra; and the lichen tundra is subdivided into Cladonia tundra, Platysma tundra, and Alectoria heath.
Above this grows a species of pine, which becomes dwarfed and disappears at an altitude of about 6000 ft., beyond which is a zone of lichen and moss covered or almost bare rock.
The algal cells are never known to form spores while part of the lichen-thallus, but they may do so when separated from it and growing free.
In 1865 De Bary suggested the possibility that such lichens as Collema, Ephebe, &c., arose as a result of the attack of parasitic Ascomycetes upon the algae, Nostoc, Chroococcus, &c. In 1867 the observations of Famintzin and Baranetzky showed that the gonidia, in certain cases, were able to live outside the lichen-thallus, and in the case of Physcia, Evernia and Cladonia were able to form zoospores.
Although Schwendener supported this view of the " dual " nature of lichens by very strong evidence and identified the more common lichen-gonidia with known free-living algae, yet the theory was received with a storm of opposition by nearly all lichenologists.
He investigated the exact relation of fungus and alga and showed that the same alga is able to combine with a number of different fungi to form lichens; thus Chroolepns umbrinus is found as the gonidia of 13 different lichen genera.
The view of the dual nature of lichens had hitherto been based on analysis; the final proof of this view was now supplied by the actual synthesis of a lichen from fungal and algal constituents.
The thallus or body of the lichen is of very different form in different genera.
The incense sticks and pastils known all over India under the names of ud-buti (" benzoin-light") or aggar-ki-buti (" wood aloes light") are composed of benzoin, wood aloes, sandalwood, rock lichen, patchouli, rose-malloes, talispat (the leaf of Flacourtia Cataphracta of Roxburgh), mastic and sugar-candy or gum.
Moller also in 1887 succeeded in growing small lichen-thalli without their algal constituent (gonidia) on nutritive solutions; in the case of Calicium pycnidia were actually produced under these conditions.
There are three methods of reproduction of the lichen: by fragmentation, by soredia, by the formation of fungal spores.
The ear may be regarded, fancifully, as a lichen, Umbilicaria, on the side of the head, with its lobe or drop.
- Lichen-forming Algae.
The relation of the two constituents of the lichen have been briefly stated in the beginning of this article.
Another nutritious lichen is the " Tripe de Roche " of the arctic regions, consisting of several species of the Gyrophorei, which when boiled is often eaten by the Canadian hunters and Red Indians when pressed by hunger.
But the most singular esculent lichen of all is the " manna lichen," which in times of drought and famine has served as food for large numbers of men and cattle in the arid steppes of various countries stretching from Algiers to Tartary.
LICHEN (lichen Tuber), in medical terminology, a papular disease of the skin, consisting of an eruption in small thickly set, slightly elevated red points, more or less widely distributed over the body, and accompanied by slight febrile symptoms.
The mango, lichen, pear and orange are indigenous, and several fruits and esculents have been introduced.
In the prevalent European varieties the bark is reddish-grey, and rather rough and scarred in old trees, which are often much lichen-covered.
Baranetzky therefore concluded that a certain number, if not all of the so-called algae were nothing more than free living lichen-gonidia.
The soredia are the most successful method of reproduction in lichens, for not only are some forms nearly always without spore-formation and in others the spores laregly abortive, but in all cases the spore represents only the fungal component of the thallus, and its success in the development of a new lichen-thallus depends on the chance meeting, at the time of germination, with the appropriate algal component.
Contrary to the behaviour of the non-lichen forming Ascomycetes the lichen-fungi show very few cases of ordinary conidial formation.
- Section of Heteromerous Lichen Thallus.
The more important part in lichen distribution as the development of the r1012444 ordinary spores is dependent on their ?,O.° finding the proper alga on the sub- I t.?
This lichen seems unique in the fact that the fungal element is also found growing and fruiting entirely devoid of algae, while in the TRaiiine margin ? ??.:??0411 - ?
The lichen algae are not alone in their specializa tion to the symbiotic (or parasitic) mode of life, for, as stated earlier, the fungus appear in the majority of cases to have completely lost the power of independent development since with very rare exceptions they are not found alone.
These excretory products have usually an acid nature and hence are generally known as lichen-acids.
Zukal has considered that the lichen acids protect the lichen from the attacks of animals; the experiments of Zopf, however, have cast doubt on this; certainly lichens containing very bitter acids are eaten by mites though some of the acids appear to be poisonous to frogs.
The dual nature of the lichen thallus introduces at the outset a classificatory difficulty.
Thus in the case of saxicolous lichens the mineralogical character of the rock has of itself little or no influence upon lichen growth, which is influenced more especially and directly by their physical properties, such as their capacity for retaining heat and moisture.
2), a rootless plant, which hangs in long grey lichen-like festoons from the branches of trees, a native of Mexico and the southern United States; the water required for food is absorbed from the moisture in the air by peculiar hairs which cover the (From The Botanical Magazine, by permission of Lovell, Reeve & Co.) FIG.
Lichen Kanons, ii.
The highest specimen obtained was a lichen (Lecanora subfusca, L.) on the south side of Chimborazo, 18,400 ft.
Many of them enter into the structure of the lichen-thallus, as the so-called gonidia.
At the other extreme the cell-walls of many lichen-fungi are soft and colourless, but turn blue in iodine, as does starch.
In such districts lichen vegetation is entirely or almost entirely absent.
The lichen flora of temperate regions again is essentially distinguished from the preceding by the frequency of corticolous species belonging to Lecanora, Lecidea and Graphidei.