THALLOl'HYTES: FUNGI 



81 



pendently of the fungus. In fact, the enmeshed Algae are 

 often recognized as identical with forms living independ- 

 ently, those thus used being various Blue-green, Protococ- 

 cus, and Conferva forms (see p. 87). 



On the other hand, the fungus symbiont has become 

 quite dependent upon the alga, and its germinating spores 

 do not develop far unless the young mycelium can lay hold 

 of suitable Algae. At certain times cup-like or disk-like 

 bodies appear on the surface of the lichen thallus, with 

 brown, or black, or more brightly-colored lining (Figs. 70, 

 71). These bodies are the apothecia, and a section through 

 them shows that the colored lining is largely made up of 

 delicate sacs containing spores (Figs. 73, 74). These sacs 

 are evidently asci, the apothecia correspond to ascocarps, 

 and the Lichen fungus proves to be an Ascomycete. 



FIG. 73. Section through an apothecium of Anaptychia, showing stalk of the cup 

 (m), masses of algal cells (g), outer margin of cup (?), overlapping edge (t, t), layer 

 of asci (h), and massing of hyphae beneath asci (y). After SACHS. 



Certain Ascomycetes, therefore, have learned to use cer- 

 tain Algae in this peculiar way, and a Lichen is the result. 

 Some Basidiomycetes have also learned the same habit, and 

 form Lichens. 



Various forms of Lichen bodies can be distinguished as 

 follows : (1) Crustaceous Lichens, in which the thallus resem- 



