EU-MYCETES.~(a) A$COMYCLTES 



439 



susceptible to impurities in the air, and are absent 



areas (Fig. 372). 



Their structure shows two distinct constitucni., .....,„ ...,., 

 have Algal characters, and often closely resemble Algae known ,n 

 the free state ; they contain chlorophyll or some related colouring 

 matter, and are photo-synthetic. They are distributed vanously 

 m the thallus, often in a definite gonidial layer. These cclU arf 

 closely invested by the fungal constituent, which is composed of 





-->=:) 



Fig. 373- 

 Cladoniafurcata. A = vertical section of the t)iallui>how :i 

 layer below the cortical sheath ( x 330). B = part of the sa:. 

 show the mode of attachment of the hyphae to the gouidia ( - 



to 

 ; Uornn ) 



septate and branched hyphae, twigs of which enwrap the Algal cclb, 

 establishing intimate physiological relations (Fig. }"/}). Not only 

 does this dual organism flourish, but it may also propagate .15 stich. 

 In wet weather many Lichens arc covered by a mealy powder, extruded 

 from within. Examination shows that it is composed of soredtAi, 

 which are bodies containing both constituents of the th " .nd 



each soredium is thus able to grow directly into a new I.i' . 



The fruiting bodies of the Lichens are, however, produced from 

 the Fungal constituent only, and most of them closely resemble those 

 of Disco-mycetous and Pyreno-mycctous Fungi in form and con- 

 struction (Fig. ^72, A). In tiic Iceland Moss (Cctraria Islandua), which 



