Definify.com
Webster 1913 Edition
Lichen
Li′chen
(lī′kĕn; 277)
, Noun.
[L., fr. Gr.
λειχήν
.] 1.
(Bot.)
One of a class of cellular, flowerless plants, (technically called
Lichenes
), having no distinction of leaf and stem, usually of scaly, expanded, frond-like forms, but sometimes erect or pendulous and variously branched. They derive their nourishment from the air, and generate by means of spores. The species are very widely distributed, and form irregular spots or patches, usually of a greenish or yellowish color, upon rocks, trees, and various bodies, to which they adhere with great tenacity. They are often improperly called rock moss
or tree moss
. ☞ A favorite modern theory of lichens (called after its inventor the Schwendener hypothesis), is that they are not autonomous plants, but that they consist of ascigerous fungi, parasitic on algæ. Each lichen is composed of white filaments and green, or greenish, rounded cells, and it is argued that the two are of different nature, the one living at the expense of the other. See
Hyphæ
, and Gonidia
. 2.
(Med.)
A name given to several varieties of skin disease, esp. to one characterized by the eruption of small, conical or flat, reddish pimples, which, if unchecked, tend to spread and produce great and even fatal exhaustion.
Webster 1828 Edition
Lichen
LICH'EN
,Noun.
1.
In botany, the name for an extensive division of cryptogamian plants, constituting a genus in the order of Algae, in the Linnean system, but now forming a distinct natural order. They appear in the form of thin flat crust, covering rocks and the bark of trees, or in foliaceous expansions, or branched like a shrub in miniature, or sometimes only as a gelatinous mass, or a powdery substance. They are called rock moss and tree moss, and some of the liverworts are of this order. They also include the Iceland moss and the reindeer moss; but they are entirely distinct from the true mosses (Musci.)2.
In surgery, a species of impetigo, appearing in the form of a red, dry, rough, and somewhat prurient spot, that gives off small furfuraceous scales.