DISTRIBUTION 353 



epiphyllous lichens may spread to the regions beyond: Sporopodium 

 Caucasium and a sterile Strigula were found by Elenkin and Woronichin' 

 on leaves of Buxus sempervirens in the Caucasus, well outside the tropics. 



Pilocarpon, an epiphytic genus, is associated with Protococcaceae ; one 

 of the species, P. leucoblepharum, spreads from the bark to the leaves of pine- 

 trees ; it is widely distributed and has also been reported in the Caucasus^ 

 Chrysothrix, in which the gbnidia belong to the algal genus Palmella, grows on 

 Cactus spines in Chili, and may also rank as a subtropical epiphyllous lichen. 



A series of lichens from the warm temperate region of Transcaucasia 

 investigated by Steiner" were found to be very similar to those of Central 

 Europe. Lecanoraceae were, however, more abundant than Lecideaceae 

 and Verrucariaceae were comparatively rare. 



Much of Asia lies within tropical or subtropical influences. Several 

 regions have received some amount of attention from collectors. From 

 Persia there has been published a list of 59 species determined by Muller-*; 

 several of them are Egyptian or Arabian plants, 1 5 are new species, but the 

 greater number are European. 



A small collection of 53 species from India, near to Calcutta, published 

 by Nylander'', included a new genus of Caliciaceae, Pyrgidium {P. bengalense), 

 allied to Sphinctrina. He also recorded Rantalina angulosa in African species, 

 along with R. calicaris, R. farinacea and Parmelia perlata, f. isidiophora, 

 which are British. Other foliose forms, Physcia picta, Pyxine Cocoes and 

 P. Meissnerii are tropical or subtropical ; along with these were collected 

 crustaceous tropical species belonging to Lecanorae, Lecideae, Graphideae, etc. 



Leighton* published a collection of Ceylon lichens and found that Gra- 

 phideae predominated. Nylander' came to the same conclusion with regard 

 to lichens referred to him: out of 159 species investigated from Ceylon, 

 there were 36 species of Graphideae. In another list* of Labuan, Singapore 

 and Malacca lichens, 164 in all, he found that 56 belonged to the Graphidei, 

 36 to Pyrenocarpei, 14 to Thelotremei and 1 1 to Parmelei; only 15 species 

 were European. 



On the whole it is safe to conclude from the above and other publications 

 that the exceptional conditions of the tropics have produced many distinc- 

 tive lichens, but that a greater abundance both of species and individuals is 

 now to be found in temperate and cold climates. 



III. FOSSIL LICHENS 



In pronouncing on the great antiquity of lichens, proof has been adduced 

 from physiological rather than from phytogeological evidence. It would 

 have been of surpassing interest to trace back these plants through the ages, 



' Elenkin and Woronichin 1908. ^ Jaczewski 1904. ^ Steiner 1919. ^ MuUer 1892. 



' Nylander 1867. "^ Leighton 1869. ' Ny lander 1900. * Nylander 1891. 



S.L. 23 



