202 



ELEMENTS OP RTKUCTURAL BOTANY. 



layers, as in the present instance, or are scattered through 

 the body of the thallus. The presence of thpse gonidia 

 may be' said to be the distinguishing feature of the 

 Lidiens. Their true relation and function v/ere for a long 

 time doubtful, widely diiFerent opinions being held, but 



Fig. 252. 



it is now generally admitted that the gonidia are them- 

 selves chlorophyll-bearing plants^ and that the remainder 

 of the Lichen is a true Fungus, parasitic upon, the gonidia. 



Fig. 252. — ^Very higrhly magnified view of section of tlie thallus of a Lichen ; 

 r, rhizoids; m, spurious tissue of hyphse ; g, green gonidia; o, boundary 

 cells of upper side ; u, boundary cells of under side. (Sachs.) 



