138 



thallus presents almost the same external appearance as to color and 

 conformation, but the minute anatomy is somewhat different. The 

 algae are Cystococcus humicola, very intimately associated with 

 the haustoria, both ectotrophic and endotrophic ; this union is so 

 intimate that it is almost impossible to separate the symbionts with- 

 out destroying the algae or the hyphae. The upper layer of the 

 thallus contains the remnants of numerous dead algae whose contents 

 have been absorbed by the haustoria. The algae are evidently soon 

 exhausted by the absorbing haustoria, which necessitates the for- 

 mation of new algal cells by division. The algal cells are quite 

 variable in size, which seems to depend upon the intimacy of their 

 union with the hyphae ; if they are enclosed by few haustoria they 

 may develop to considerable size before dividing. 



As in Catillarid) the hypothecium is black or dark blue. 1 The 

 entire thecium is likewise more or less blue-black. The spore-sacs 

 contain one, rarely two, large simple spores. The two layers of the 

 spore-wall are very distinct ; the outer layer (exosporium) is quite 

 thick and gelatinous, which enables the spore to adhere to any sub- 

 stratum when moist. 



This genus, which is likewise separated from Heterothecium, is 

 represented by a single species (M. sanguinaria) . It is not very 

 common, occurring upon tree trunks, and is readily recognized by the 

 comparatively large convex apothecia upon the light grey thallus. 



PLATES 22 AND 23. 

 MEGAI.OSPORA SANGUINARIA (L.) Kbr. 



1 . Plant natural size. 



2. Section of apothecium. 



3. Section of thallus. 



a, dermal layer ; b, algal layer ; c, medullary layer (compare with 

 c of plate 21. 



4. Spore-sac with spore and paraphyses. 



<;. Spores; a, gelatinous exosporium ; b, endosporium. 

 6. Algae (a) and hyphae (b) ; c, pyrenoid bodies. 



12. LOPADIUM Kbr. Syst. Lich. Germ. 210. 1855. 

 Some authors include this group of lichens in the conglomerate 

 genus Heterothecium. It is represented by a few well-characterized 

 species. 



1 European specimens are said to have a colorless hypothecium. Some authors 

 recognize varieties based upon the " red " or " vellowish " color of this structure. 



