The English flora - SeaweedAfrica

LICHENES.
1
Ord. IV. LICHENES.
Ach. Lichens.
Perennial Plants, varying- exceedingly in their form, appearance
and texture, always constituting a thallus, crust, orfrond
(universal receptacle, Ach.), which frequently spreads horizontally
upon soil, rocks, stones, the bark of trees ami dead wood, and
is pulverulent, membranaceous, coriaceous, gelatinous, filamen-
tose, and variously lobed and divided: sometimes it is erectj
variously
fruticulose and much branched; at other times pendent ;
coloured, rarely green : often the substance is simply composed
of cell 'iles, at other times the cellules are mixed with fibres.
Imperfect roots are sometimes formed, hut more for the pur-
post' of fixing the plant to its place of growth than of deriv-
ing nutriment, which appears to be alforded solely by the
air. Fructification is of two kinds : a, powdery substance, tunn-
ing indeterminate masses, or collected into more or less evident
receptacles; and, what is considered a higher state of fructification,
apothecia, or partial receptacles, which have received
different names according to their forms: scutella; or shields,
as in Lecanora and Parmelia : patelluhe (spangles, Sm.) as in
Lecidea ; lirella, clefts, as in Opegrapha ; mycina, a- in ];