18 Proceedings of the Royal Irish Academy. 



so-called varieties of B. calicaris, with the exception of S. canaliculate 

 recognized as species, and gives in detail the histological and physical 

 peculiarities of the tissues concerned. Briefly, he recognizes an outer cortex, 

 a gonidial layer and a medulla in all varieties, the relative development of 

 cortex and medulla being in some cases characteristic ; he distinguishes two 

 opposed cortices, an upper and an under ; he notes the more or less loose 

 nature of the medullary tissue, and the fact that the gonidial layer is an 

 interrupted one, sometimes penetrating the lichen cortex. In his detailed 

 account of the cortex he asserts thru the apical swellings of the longitudinally 

 arranged hyphae are disposed at ri.'ht angles to the surface, being firmly laid 

 together to form the very smooth surface of the lichen. The cortical hyphae 

 are described as thin tubes with fine lumen and thick walls, and as being 

 bound together by a cement, the decomposition product of the cell walls ; 

 this is stated to be an easily soluble, structureless substance lying between 

 the cells ; no cross walls could be found. 



In 1860-2 Schwendener 1 published his researches on the lichen thallus. 

 Be regards the outermost laj 3 rechneider's "apical swellings," as the 

 true ooi internally by strands of mechanical tissue, which 



-ist.s "f longitudinally arranged hyphae. lie recognizes cross walls and 

 regards the - substance" as a part of the thick hyphal wall, 



supposing t: - rschneider mistook the lumina of the cortical cells for 

 the complete cells and their valla. He distinguishes in all epiphloeodic 

 lichens, whether crustaoeous or foliaceous, a basal layer or disc of tissue, free 

 from algal a ring within the periderm and serving for attachment 



and nourishment. This he names the " bypothaJlus," remaining in the 

 substratum under the " protothallns." In the former term he includes 

 rhuoids of folioc . basal discs of strap lichens and gonidialess hyphal 



layers of erustaoeous licb 



He further states with a b the mode of attachment, that in Usnea 



the attachment-poinl . ise to rows of hyphae which take root round 



projections of the bark, thus fastening the lichen to the substratum, and that 

 these attaching hyphae arise from the medullary tissue. In 1894 Crombie, 2 

 in his monograph, following Xylander, 5 distinguishes between species of 

 lalina having an amorphous and those having a filamentous cortex, most 

 of the corticolous species coming under the latter heading. He describes the 



1 Schwendener. '• Untenuchungen Gber den Flechtenthallua " (Xageli's Beitrage z. w. 

 Botanik, - 



5 Crombie, J. M. A Monograph of Lichens found in Britain. London, 1894. 



1 Nvlander, W. Kecognilio monographic* Ramalinarnm (Bull. Soc. Linn, de Norm. 

 2 iv, 1868-9). 



