172 

 PLATE 46. 



EVERNIA VULPIXA (L.) Ach. 



1. 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 Lccan- 

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

 cclla but it is morphologically quite different. 



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

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

 related to Usnca, and hence higher in position than Evcrnia. 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 Rainalina thallus ; next follows the 

 algal layer, in which the algae ( Cystococcus) occur in colonies, con- 

 siderably larger than in Evcruia, 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 



