STRATOSE-RADIATE THALLUS 



121 



a continuous growth at the edges of the perforations, giving an unbroken 

 smooth surface and checking any irregular tearing. The enlargement of 

 the walls is solely due to intercalary growth. The origin of the reticulate 

 structure in the Clathrinae is unknown, though it is doubtless associated 



Fig. -71. Cladonia retepora Fr. From Tasmania. 



with wide podetia and rendered possible by the absence of an internal 

 chondroid layer. The reticulate structure is marvellously adapted for the 

 absorption of water: Cl, retepora, more especially, imbibes and holds moisture 

 like a sponge. 



F. ROOTING STRUCTURES OF CLADONIAE 



The squamules of the primary thallus are attached, as are most squa- 

 mules, to the supporting substance by strands of hyphae which may be 

 combined into simple or branching rhizinae and penetrate the soil or the 

 wood on which the lichen grows. There is frequently but one of these 

 rooting structures and it branches repeatedly until the ultimate branchlets 

 end in delicate mycelium. Generally they are grey or brown and are not 



