Page:The American Cyclopædia (1879) Volume X.djvu/416

 410 LICHENS small black dots, either upon the margin only or scattered over its surface, called spermo- gonia. A magnified cross section (fig. V) shows a great number of needle-shaped, extremely minute bodies, the spermatia, which are borne by branched or simple filaments called sterig- mata. The spermatia are present or absent in different species, and vary considerably in form, which is constant for each species in which they occur. Seasoning from analogy, the spermatia have been supposed to be equiva- lent to the antheridia in ferns and mosses, and to play the part of the male organ in fertilizing the spores; but as their action has not been observed, and they have not the locomotive power of the antheridia, their office is inferred rather than proven. Pycnidia are still other protuberances upon the surface of the thallus of some lichens ; they are not of common oc- currence, and their office is not well under- stood ; as they contain spore-like bodies, they are regarded by Tulasne as supplementary means of propagation. The close relationship of lichens with algce and fungi has already been alluded to ; indeed, Schwendener goes so far as to deny to lichens the rank of a distinct order? but re- gards them as compound organisms consisting of algas held in captivity by the meshes of a fun- gus ; a view which meets with but few adherents. The essential elements of terrestrial vegeta- tion are to be found in these plants, which hold such a subordinate rank in the scale of creation, being in fact rootless and cellular, subsisting upon the air, but furnished with stems, branch- es, and parts which correspond to fruits and seeds ; their position in the vegetable kingdom being intermediate between the floating tribes of the alga3 and the fugacious forms of the fungi, or, as Fries expresses it, "having the vegetation of the algals and the fructification of the fungals." Thus ingeniously contrived and admirably fitted for an especial office, we should expect to find them in situations suited to no other vegetation. Lichens play an important part in the economy of nature, and it is proba- ble that they were the first forms of vegetation upon the dry rocks ; and that by their decay and accompanying disintegration of the rocks they began the accumulation of soil. It is now well known that the pulverulent lichens are the first plants that clothe the bare rocks of newly formed islands in the midst of the ocean ; the foliaceous lichens follow these, then mosses and liverworts, which by their decay prepare a soil for the growth of plants of the higher orders. The crustaceous lichens affect the very summits of mountains, growing near the limits of perpetual snow, and are seen very far north, so seemingly rudimentary as to appear like colored spots of the solid rocks. They are not, however, exclusively confined to such re- gions, being common in some instances on the margin of the sea in countries where granitic strata especially are to be found. The sides of buildings and the surfaces of sandstone rocks .are favorite situations for many kinds. The larger and more conspicuous are found in tem- perate and moist climates, choosing in the northern hemisphere northern and western exposures ; and even at the equator there are species rich and gorgeous in colors. The pre- vailing tints in lichen are gray, white, black, dark brown, rich green, pale yellow, and or- ange red. From mere specks or patches of hard, seemingly inanimate matter, the lichens assume sizes of considerable magnitude. The change produced by moisture in the same plant is very striking : dull and inconspicu- ous in dry weather, it assumes bright colors in a prolonged season of dampness, and ap- pears endowed with life. Lichens grow upon almost every substance where alternate dry- ness and moisture can be found, a very few only passing much of their existence in a sub- merged state. Destitute of roots and depen- dent upon the atmosphere for their nutrition, it seems to matter little with them upon what matrix they fix. Some have even been found attached to the glass in the windows of old and deserted buildings. In so wide a geographical range as that over which they are spread, the same identical species must be found occurring upon very distinct kinds of trees and soils, yet maintaining their specific characters. Thus there are some species which are most com- monly to be expected upon rocks, yet which frequently grow upon the bark of trees. Many species are excessively polymorphous, and pre- sent themselves under so many varieties as to render it difficult to reduce them to an original type, the color of the thallus being often af- fected by the chemical composition of the rock on which they grow, or the color of the disk of the apothecia remarkably diverse. Sev- eral species are parasitical upon others, occur- ring upon their thalli in the reduced forms of mere fruits or of spermagonia ; their own vege- tative functions being supplied by the subject to which they have attached themselves. The value of the lichens to man may be estimated from their uses as articles of food and of med- icine, and from their employment in the arts. According to Linnaeus, in the arctic regions of Lapland the reindeer lichen (cladonia rangi- ferina) grows in the utmost profusion, and overspreads plains hundreds of miles in extent. These are the fertile fields of the Laplanders, so that the possessor of such a barren tract thus covered with lichens considers himself fortunate ; for when the cold of winter has withered up every sort of herbage, this lichen becomes the principal aliment of the herds in which consists his wealth, and on which de- pends the very existence of the natives of that country. The reindeer lichen was at one time by edict of Gustavus III. of Sweden used in the manufacture of flour, when grain Avas scarce. It also grows in this country as far south as Penn- sylvania, and is especially abundant northward to Canada and arctic America. The Iceland moss (cetraria Islandicd) fattens cattle, sheep, deer, and swine ; and out of this and of the G.