202 



ELEMENTS OF STRUCTURAL BOTANY, 



layers, us in the present instance, or arc scattered through 

 the body of the thallus. The presence of these gonidia 

 may be said to. be the distinguishing feature of the 

 Lichens. Their true relation and function wore for a long 

 time doubtful, widely different 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 hi'/hly magnified view of section of the th.illus of a Lichen : 

 r, rhizoids ; in, spurious tissue of hyphae ; g, green gonidia; o, boundary 

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



