Li"chen (lī"k&ebreve;n; 277), n.
[L., fr. Gr. leichh`n.] 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.
&fist; 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.
