LICHENES. 



Ord. IV. LICHENES. 1 Ach. Lichens. 



Perennial Plants, varying- exceedingly in their form, appear- 

 ance and texture, always constituting a thallus, crust, or frond 

 (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 

 fruticulose and much branched; at other times pendent ; variously 

 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 fructifica- 

 tion, 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 ];<<<>- 

 myces ; pilidia (jaij/'s, Sm.) as in Calicium ; orbillce, as in 

 / snea ,• pelta, targets, as in Peltidea ,• trica or gyromata {buttons. 

 Sin.) as in Gyrophora ; tubercula, tubercles, as in Verruoaria; 

 cistuke, {cellules, Sm.) as in Sphcerophoron ; eephalodia, (knobs, 

 Snu) as in Scyphophorus, (when the stalk which bears them is 

 called podetium); pulvinuli (naked sporules), as in Spiloma; 



variolic (pU8tules\ 96 in I ariolar/a : — these, for the most part, 

 are sessile, perennial, and contain a • omewhat waxy plat 



layer, (himina prolrgera, AcJu) in which are imbedded seeds, 

 or sporules, enclosed in little membranous tubes or th 



The Licit, ns are. perhaps, more nearly allied to the / 



than to the Alga, in general appearance. Some /' long 



the former, resemble certain Lichens, destitute of, or with an 

 imperfect, thallus; and the Genus Lichina i- considered by 



many l«» hi\«- a- great :i claim !•• rank with the lAchtM M 



among the Alga, in which ii is usually placed. \\\ the Genus 

 Endocarpon they approach the Hepaticc . They are among the 



1 Prom i '. irhich the fructification* often resemble. 



I 



