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XI. 



ON THE ATTACHMENT OEGANS OF SOME COMMON 

 PAEMELIAE. 



By LILIAN PORTER, M.Sc. 



Plates XXI-XXIII. 



Read November 11, 1918. Published January 10, 1919. 



I. — Introduction. 



Among foliaceous lichens the genus Parmelia is characterized by a simple 

 type of anatomical structure which persists in species differing widely in 

 general habit, colour, segmentation, and habitat. The upper cortex consists 

 of a distinct layer of branched, septate hyphae, running at right angles to 

 the surface ; below this is a gonidial layer with Protococcus gonidia and a 

 medullary layer of loosely woven hyphae, running more or less parallel to 

 the surface. 



The under cortex as a rule resembles the upper. Reinke 1 states that the 

 upper, as the under, side is covered by a thickly woven horny cortex ; but it 

 will be seen later that exceptions to this generalization occur. Zahlbriickner's 2 

 statement that the under cortex is usually dark-coloured, applies without 

 restriction to all species which are dorsiventral in habit. 



The variations in colour and in distribution of rhizines and papillae 

 exhibited by the imder-surface are valuable aids to identification of species, 

 and have been well described by Lindau. 3 



The following studies deal with these variations microscopically and in 

 greater detail than was necessary for the pioneei work of the same author 4 

 on the subject of attachment organs of lichens. The methods used are those 

 described previously for a similar study of the Ramalinae, and the materials 



1 Reinke, J. Abhaudlungen uber Flechten IV. Pringsheim's Jahrbiicher f. w. 

 Botanik 28, 1895, p. 385. 



2 Zahlbriickner, A. " Flechten " in Engler und Prantl's Natiirlichen Ptlanzenfaniilien 

 Ti'el I*. B Specieller Teil, 1907, p. 211. 



3 Lindau, G. Die Flechten. Berlin, 1913, p. 184 et seq. 



4 Lindau, G. Lichenologische Untersuchungon I, Uber Wachstum und Anheftungs- 

 weise der Rindentiechten. Dresden, 1895. 



5 Porter, L. On the attachment organs of the common corticoloua Ramalinae. 

 Proc. Roy. Irish Acad., xxxiv, B, 2, 1917. 



R.I. A. PROO., VOL. XXXIV, SliCT. B. [2 A] 



