262 



ELEMENTS otv STRUCTURAL. BOTANY. 



layers, as in the present instance, or are 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 were 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 highly magnified view of section of the 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.) 



