172 

 PLATE 46. 



EVERNIA VUJLPINA (L.) Acll. 



i . Portion of thallus natural size. 



2. Section of apothecium. 



a, thecium; b and c, layers of the hypothecium ; d, algal layer; e r 

 medullary tissue; e, mechanical tissue (hyphae) ; f, algal layer ; 

 g, protecting and mechanical tissue. 



3. Radial transverse segment of thallus. 



a, outer covering corresponding to 2 g ; b, algal layer; c, medullary 

 tissue; d, mechanical bundle cut transversely. 



4. Paraphyses and spore-sac. 



5. Spores. 



9. Ramalina Ach. Lich. Univ., 122. 1810. 



The phyletic relationship of this group is as yet undetermined. 

 According to the spore-characters it is not derived from the Lecan- 

 oras or Parmelias; some authors regard it as closely related to Ro- 

 cella but it is morphologically quite different. 



The position of the genus is also somewhat uncertain. Micro- 

 scopically considered, some of the forms (R. linearis) are closely 

 related to Usnea, and hence higher in position than Evernia. Its 

 mechanical adaptations seem to indicate a lower position. 



The thallus, although fruticose in all the species, always remains 

 flattened. In this genus we have the centric structure well charac- 

 terized, with a radial tendency in some of the forms. The tissue- 

 layers are quite constant throughout the genus and are essentially as 

 follows : An outer layer, quite well developed, consisting of closely 

 agglutinate hyphae extending parallel to the long axis of the thallus ; 

 sometimes this tissue is interwoven with hyphae which extend for 

 the most part radially horizontal ; this layer constitutes the protec- 

 tive and mechanical tissue, differing quite materially from the outer 

 layer in Evernia, not only structurally, but also in the absence of the 

 numerous acid crystals, which accounts for the comparative smooth- 

 ness of the outer surface of the Ramalina thallus ; next follows the 

 algal layer, in which the algae (Cysto 'coccus) occur in colonies, con- 

 siderably larger than in Evernia, otherwise much the same. The 

 entire interior is occupied by a medullary tissue, consisting of loosely 

 interwoven hyphae. It should, however, be remarked that occasion- 

 ally there are a few scattered mechanical hyphae nearer the algal 



