DERIVATION OF THE FLORA AND FAUNA 289 



are interrelated in such a manner that we can derive the genera from a common 

 Antarctic centre. This is a problem that only an expert and all-round hepatologist 

 can solve. In our island case the result may be that the Antarctic element will 

 shrink and the Neotropical swell; we may have to merge the Chilean element in 

 the Neotropical. Disregarding the cosmopolitan species, anthropophilous and anthro- 

 pochorous and very likely of recent introduction, we find that the bulk of the 

 Chilean species is formed by the 14 species of Plagiochila\ we need a critical 

 revision of this gigantic assemblage before we shall know anything of its origin 

 and history. Also small but widely scattered genera offer difficulties: ^/^^i-Zr^'//^, 

 Adelanthus and Herberta, for instance. 



The discontinuous distribution of many southern genera and several species 

 was commented upon by Miss Fulford (/oj. 846): 



The distribution patterns indicate that they were contemporaries at a time when free 

 migration was possible between South America, Africa, Australia, New Zealand and the 

 Sikkim area in N.E. India. They also indicate that the Antarctic Continent has been of 

 great importance in the distribution of genera and identical species in South America, the 

 Antarctic Islands [rm^ Subantarctic], Australia— New Zealand and probably Africa. 



Finally, let us repeat our comparison of the four phyla analyzed. No obviously 

 Arcto-tertiary (Boreal) species were distinguished among the Hepaticae. The Chilean 

 element accepted in the mosses and hepatics has been combined with the Neotropical 

 to form a Neotropical-Chilean group (NC); A, Antarctic; B, Boreal. 



Table V. 



A NC B 



Angiosperms 42.2 36.7 15.6 



Pteridophytes 60.4 37.7 1.9 



Mosses 55.8 41.7 2.5 



Hepatics 67.7 32.3 — 



V. Lichenes. 



Unlike the Archegoniates the Lichens offer insuperable difficulties when we 

 try to trace eventual centres of origin and evolution. Of 67 genera represented in 

 Juan Fernandez no less than some 55 have a wide, in cases world-wide distribu- 

 tion; they are called cosmopolitan, subcosmopolitan, tropical, temperate and so 

 forth, and with regard to about 70 species the situation is the same. Only in a 

 very limited number of instances a genus, or a group of related species is, to 

 judge from its present distribution, concentrated to a limited area, tempting us 

 to consider it a centre of evolution. On the other hand we must not forget that 

 lichens are lichenized fungi; modern lichenologists do not regard them as a spe- 

 cial phylum but range them with the different fungus orders and families accord- 

 ing to the taxonomic position of the fungus component. Nothing prevents us 

 from assuming that the same lichen species originated in different places widely 

 apart where both fungus and microscopic alga happened to be present at the time 

 when lichen-forming fungi existed as independent organisms. Nor should it be 



19 ~ 557857 The Nat. Hist, of Juan Fernandez and Easter Isl. Vol. I 



