STRATOSE-RADIATE THALLUS 115 



thus distinguishing it from the purely hyphal stalks of the apothecia in 

 Caliciaceae. Even in the genus Baeomyces, 

 while the podetia of some of the species 

 are without gonidia, neighbouring species 

 are provided with green cells on the up- 

 right stalks clearly showing their true 

 affinity with the Cladoniae. In one British 

 species of Cladonia (CL caespiticid) the 

 short podetium consists only of the fibrous 

 chondroid cylinder, and thus resembles the 

 apothecial stalk of Baeomyces rufus, but 

 in that species also there are occasional 

 surface gonidia that *may give rise to 

 squamules. 



Krabbe 1 concluded from his observa- 

 tions that the podetial gonidia of Cladonia 

 arrived from the open, conveyed by wind, 

 water or insects from the loose soredia that 

 are generally so plentiful in any Cladonia 

 colony. They alighted, he held, on the 

 growing stalks and, being secured by the 

 free-growing ends of the exterior hyphae, 

 they increased and became an integral part of the podetium. In more 

 recent times Baur 2 has recalled and supported Krabbe's view, but Wainio 3 , 

 on the contrary, claims to have proved that in the earliest stages of the 

 podetium the gonidia were already present, having been carried up from 

 the gonidial zone of the primary thallus by the primordial hyphae. Increase 

 of these green cells follows normally by cell-division or sporulation. 



Algal cells have been found to be common to different lichens, but in 

 Cladoniae Chodat 4 claims to have proved by cultures that each species 

 tested has a special gonidium, determined by him as a species of Cystococcus, 

 which would render colonization by algae from the open much less probable. 

 In addition, the fungal hyphae are specific, and any soredia (with their 

 combined symbionts) that alighted on the podetium could only be utilized 

 if they originated from the same species ; or, if they were incorporated, the 

 hyphae belonging to any other species would of necessity die off and be 

 replaced by those of the podetium. 



c. CORTICAL TISSUE. In some species a cortex of the decomposed type 

 of thick-walled conglutinate hyphae is present, either continuous over the 

 whole surface of the podetium, as in CL gracilis (Fig. 68), or in interrupted 



Fig. 67. Cladonia squatnosa Hoffm. Ver- 

 tical section of podetium with early 

 stage of central tube and of podetial 

 squamules x 100 (after Krabbe). 



1 Krabbe 1891. 



Baur 1904. 



3 Wainio 1880. 



4 Chodat 1913. 



