354 SYSTEMATIC 



even if it were never possible to assign to any definite period the first, 

 symbiosis of the fungus and alga ; but among fossil plants there are only 

 scanty records of lichens and even these few are of doubtful determination. 



The reason for this is fairly obvious : not only are the primitive thalline 

 forms too indistinct for recognizable preservation, but all lichens are charac- 

 terized by the gelatinous nature of the hyphal or of the algal membranes 

 which readily imbibe water. They thus become soft and ilaccid and unfit 

 to leave any impress on sedimentary rocks. It has also been pointed out by 

 Schimper' that while deciduous leaves with fungi on them are abundant in 

 fossil beds, lichens are entirely wanting. These latter are so firmly attached 

 to the rocks or trees on which they grow that they are rarely dislodged, and 

 form no part of wind- or autumn-fall. Trunks and branches of trees lose 

 their bark by decay long before they become fossilized and thus all trace of 

 their lichen covering disappears. 



The few records that have been made are here tabulated in chronological 

 order: 



1. Palaeozoic. Schimper decides that there are no records of lichens 

 in the earlier epochs. Any allusions^ to their occurrence are held to be ex- 

 tremely vague and speculative. 



2. Mesozoic. Braun' has recorded a Ramalinites lacerus from the 

 Keuper sandstone at Eckersdorf, though later^ he seemed to be doubtful as 

 to his determination. One other lichen, an Opegrapha, has been described' 

 from the chalk at Aix. 



3. Cainozoic. In the brown-coal formations of Saxony Engelhardt" 

 finds two lichens : Ramalina tertiaria, a much branched plant, the fronds 

 being flat and not channelled " and of further interest that it is attached to 

 a carbonized stem." The second form. Lichen dichotomus, has a dichoto- 

 mously branching strap-shaped frond. " There is sufficient evidence that 

 these fronds were cylindrical and that the width is due to pressure. In one 

 place a channel is visible, filled with an ochraceous yellow substance." 



Other records on brown coal or lignite are : Verrucarites geanthricis'' ' 

 Goepp., somewhat similar to Pyrenula nitida, found at Muskau in Silesia ; 

 Opegrapha Thoniasiana^ Goepp., near to Opegrapha varia, and Graphis scripta 

 succinea Goepp.' on a piece of lignite in amber beds, all of them doubtful. 



Schimper has questioned, as he well might, Ludwig's" recqrds from 

 lignite from the Rhein-Wetterau Tertiary formations ; these are : Cla- 

 donia rosea, Lichen albineus, L. diffissus and L. orbiculatus ; he thinks they 

 are probably fungus mycelia. Another lichen, a Parmelia with apothecia, 



^ Schimper 1869, p. 145. ^ Lindsay 1879. '• Braun 1840. '' Muenster 1846, p. id- 



° Elting.shausen and Debey 1857. ' Engelhardt 1870 (PI. I. figs, i and 2)., 



' Goeppert 1845, p. 195. ^ See Schimper 1869, pp. 145, etc. 



"Goeppert and Menge 1883, t. 1, fig. 3. l" Ludwig 1859, p. 61 (t. 9, figs. 1-4), 1859-61. 



