The water moved silently over moss and lichen covered slabs of rocks, forming small pools in the low spots.
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.
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.
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 reproductive organs of the lichen are of a typically fungal character, i.e.
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.
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.
The thallus or body of the lichen is of very different form in different genera.
There are three methods of reproduction of the lichen: by fragmentation, by soredia, by the formation of fungal spores.
The lichen, however, is able to grow as the alga supplies organic food material and the fungus has developed a battery of acids (see below) which enable it actually to dissolve the most resistant rocks.
The relation of the two constituents of the lichen have been briefly stated in the beginning of this article.
The fungus seems, on the other hand, to stimulate the algal cells to special development, for those in the lichen are larger than those in the free state, but this is not necessarily adverse to the idea of parasitism, for it is well known that an increase in the size of the cells of the host is often the result of the attacks of parasitic fungi.
The real attractions of the Hollowell farm, to me, were: its complete retirement, being, about two miles from the village, half a mile from the nearest neighbor, and separated from the highway by a broad field; its bounding on the river, which the owner said protected it by its fogs from frosts in the spring, though that was nothing to me; the gray color and ruinous state of the house and barn, and the dilapidated fences, which put such an interval between me and the last occupant; the hollow and lichen-covered apple trees, gnawed by rabbits, showing what kind of neighbors I should have; but above all, the recollection I had of it from my earliest voyages up the river, when the house was concealed behind a dense grove of red maples, through which I heard the house-dog bark.
Sometimes I rambled to pine groves, standing like temples, or like fleets at sea, full-rigged, with wavy boughs, and rippling with light, so soft and green and shady that the Druids would have forsaken their oaks to worship in them; or to the cedar wood beyond Flint's Pond, where the trees, covered with hoary blue berries, spiring higher and higher, are fit to stand before Valhalla, and the creeping juniper covers the ground with wreaths full of fruit; or to swamps where the usnea lichen hangs in festoons from the white spruce trees, and toadstools, round tables of the swamp gods, cover the ground, and more beautiful fungi adorn the stumps, like butterflies or shells, vegetable winkles; where the swamp-pink and dogwood grow, the red alderberry glows like eyes of imps, the waxwork grooves and crushes the hardest woods in its folds, and the wild holly berries make the beholder forget his home with their beauty, and he is dazzled and tempted by nameless other wild forbidden fruits, too fair for mortal taste.
The ear may be regarded, fancifully, as a lichen, Umbilicaria, on the side of the head, with its lobe or drop.