STRATOSE-RADIATE THALLUS 123 



considered them as part of the sporiferous organ. This view was also held 

 by some of the earliest lichenologists: Necker 1 , for instance, constantly 

 referred to the upright structure as "stipes"; Persoon 2 included it, under 

 the term "pedunculus," as part of the "inflorescence" of the lichen, and 

 Acharius 8 established the name "podetium" to describe the stalk of the 

 apothecium in Baeomyces. 



Later lichenologists, such as Wallroth 4 , looked on the podetia as advanced 

 stages of the thallus, or as forming a supplementary thallus. Tulasne 5 

 described them as branching upright processes from the horizontal form, 

 and Koerber 6 considered them as the true thallus, the primary squamule 

 being merely a protothallus. By them and by succeeding students of lichens 

 the twofold character of the thallus was accepted until Wainio and Krabbe 

 by their more exact researches discovered the endogenous origin of the 

 podetium, which they considered was conclusive evidence of its apothecial 

 character: they claimed that the primordium of the podetium was homolo- 

 gous with the primordium of the apothecium. Reinke 7 and Wainio are in 

 accord with Krabbe as to the probable morphological significance of the 

 podetium, but they both insist on its modified thalline character. Wainio 

 sums up that: "the podetium is an apothecial stalk, that is to say an 

 elongation of the conceptacle most frequently transformed by metamorphosis 

 to a vertical thallus, though visibly retaining its stalk character." Sattler 8 , 

 one of the most recent students of Cladonia, regards the podetium as evolved 

 with reference to spore-dissemination, and therefore of apothecial character. 

 His views are described and discussed in the chapter on phylogeny. 



Reinke and others sought for a solution of the problem in Baeomyces, 

 one of the more primitive genera of the Cladoniaceae. The thallus, except 

 in a few mostly exotic species, scarcely advances beyond the crustaceous 

 condition; the podetia are short and so varied in character that species 

 have been assigned by systematists to several different genera. In one of 

 them, Baeomyces roseus, the podetium or stalk originates according to 

 Nienburg 9 deep down in the medulla of a fertile granule as a specialized 

 weft of tissue ; there is no carpogonium nor trichogyne formed ; the hyphae 

 that grow upward and form the podetium are generative filaments and give 

 rise to asci and paraphyses. In a second species, B. rufus (Sphyridium), the 

 gonidial zone and outer cortex of a thalline granule swell out to form a 

 thalline protuberance; the carpogonium arises close to the apex, and from 

 it branch the generative filaments. Nienburg regards the stalk of B. roseus 

 as apothecial and as representing an extension of the proper margin 10 (ex- 

 cipulum proprium), that of B. rufus as a typical vegetative podetium. 



1 Necker 1871. 2 Persoon 1794. 3 Acharius 1803. 4 Wallroth 1829, p. 61. 



5 Tulasne 1852. 6 Koerber 1855. 7 Reinke 1894. 8 Sattler 1914. 



9 Nienburg 1908. 10 See p. 183. 



