FUNGI 



161 



are not single plants, but 

 that each lichen is formed 

 of a fungus and an alga 

 living together so inti- 

 mately as to appear like 

 a single plant. In other 

 words, a lichen is not an 

 individual but a firm of 

 two individuals, very un- 

 like one another. If a 

 lichen be sectioned, the 

 relation between the two 

 constituent plants may be 

 seen (Fig. 156). The fun- 

 gus makes the bulk of the 

 body with its interwoven 

 mycelial threads, in the 

 meshes of which lie the 

 Algae, sometimes scattered, 

 sometimes massed. It is 



these enmeshed Algae, showing through the transparent my- 

 celium, that give the greenish tint to the lichen. 



Fio. 156. Cross-section of a lichen, show- 

 ing the interwoven mycelium of the 

 fungus (TO) and the enmeshed alga (g). 

 After SACHS. 



Fio. 157. Section of one of the cup-like bodies of a lichen, showing the stalk of the 

 cup (m), the masses of Algae (g), and the lining layer of asci (A). After SACHS. 



