26 Proceedings of the Royal Irish Academy. 



though only present to the extent of - 3 per cent, as shown hy Zopf. 1 In the 

 case of R. farinacea it is present to the extent of "25 per cent., in R. pollinaria 

 •16 per cent.; but undoubtedly of the three species, R. farinacea is normally 

 the lightest in colour, apart from the whitish, farinaceous appearance given 

 by its soredia. Further, if the acid be present in crystalline form it can 

 hardly appear as a structureless cement between the hyphae. Its presence 

 is commonly regarded as substantiated if the addition of caustic potash gives 

 a yellow colouration, but this generalization should be regarded with suspicion, 

 as a similar colour is given with potash by ramalic acid in R. pollinaria, by 

 cetraric arid in species of Cetraria and Cladonia, and probably by others. 

 Again, it should be noted that these acids are obtained and investigated after 

 extraction from dried and crumbled lichens by means of hot ether (Zopf) 1 or 

 milk of lime (Stenhouse, II- se),' and cannot therefore be regarded with any 

 certainty as occurring naturally in the furms described, except in the few 

 rare cases exemplified by /■'. thmusta. 



The excreted substances, acting as cements, are therefore probably of the 

 nature of lichenin, the gum-like substance occurring in Cetraria islandica, the 

 Iceland Moss ; they become mucilaginous and semi-transparent in water, as 

 noted by Speerschneider, but are hydrolyzed readily with acids, and in some 

 cases with alkalis, forming in some cases sugars, e.g. glucose from the extract 

 from /.' i prtmastri, mannite from Xanthoria parietvna. 



This gummy character would account for the adhesion of the hyphae 

 to the cell-walls of a gap in periderm tissue, enabling them to absorb the 

 decomposition products of the cellulose, according to Lindau's theory 

 (Untersuchungen, I. p, 57 >. 



In this case the basal disc must be regarded as an organ of nourishment 

 as well as of attachment, an important conclusion, involving the partial 

 independence <>f t lie fungal hyphae of their algal companions and em- 

 phasizing the symbiotic, rather than the parasitic, nature of the combina- 

 tion (Funfetuck, p. 15). 



With regard to the attachment organs themselves, three points distinguish 

 those of the Ramalinat investigated from those of Usnea and Uremia as 

 described by Schwendener and Lindau. In the first place there is no 

 limiting zone, the tissues of the thallus above and below the surface of the 

 periderm l>eing continuous. In the second, this tissue is cortical, consisting 

 of thickly-woven strands which only become loose masses at their apices 



' Zopf, W. Zur Kenntnii dur Flechtcnstnll'u vii. Annalen del Chemie, 313, 227, and 

 300. 



II' B, I I -r i linige Flechtcnstoffe. Annalen dcr Chomie, 284. 



