DERIVATION OF THE FLORA AND FAUNA 213 



Rea Hert. ex Ucne p.]). Sec 2^p. ySS. 



neriifolia Dene. Little is known of this, but it is undoubtedly a very good 

 species; micrantha Bert, ex Dene and pruinata (Johow) Skottsb. are near rela- 

 tives but good species (comp. 22g. 207). 

 Hesperoseris Skottsb. gigantea (Johow) Skottsb. See 2^p. 788. 



Vicarious species. 



VlERllAl'l'KR {2/6) distinguished between true and false vicarism. True vi- 

 carists have arisen from a common initial species and become differentiated either 

 within the limits of the area this once occupied or after penetration into a 

 <lifferent habitat, followed by isolation, whereas in the case of pseudo-vicarism 

 they have a different origin; a second species may invade the area of the first 

 and colonize such parts of the area as are unsuitable to the latter. Very often 

 the term "vicarious" has been taken in a much wider sense: any two related 

 species replacing each other in separate areas were called vicarious, and phyto- 

 geographers used the term to designate two plant species, related or not, that 

 played corresponding roles in two closely allied plant communities; in this case 

 Xothomvrcia fernaiidezhuui and Myrceugenia ScJiulzci, which form the bulk ot 

 the forest in Masatierra and Masafuera, respectively, are vicarists, although they 

 belong to different genera. Species not fulfilling the conditions claimed by VlER- 

 IIAPPER were called "substitute species". 



WULFF [2gi. 66-6^) devotes considerable space to a discussion of \icarism. 

 He agrees with ViERHAPPER: true vicarism is a result of one taxon breaking 

 up into two, adapted to different habitat conditions. Cain [42. 265) expresses 

 himself in slightly different words, but their meaning is the same: "closely re- 

 lated allopatic species which have descended from a common ancestral popula- 

 tion and attained at least spatial isolation." He summarizes statements made 

 by Drude, Diels, Wulff and Setciiell, who called species vicarious if they 

 were only slightly discontinuous morphologically but widely so geographically; 

 certainly anybody would call them vicarists but use the same term for a pair 

 of intimately related forms of which one inhabits granite and the other limestone 

 within the same geographical area. 



I am afraid that, in most cases, we know very little or nothing at all of 

 the ancestry of species we are used to call vicarious, let it be that we have 

 reason to assume that they have differentiated out of a common population some 

 time in the past. This is, at least, the situation in Juan Fernandez. Here I 

 should perhaps refer to what Cain (I.e. 276) calls polytopic species, i.e. when 

 the same taxon occurs in two or more discrete areas, disjunction being the 

 result either of dispersal from one original centre or of the breaking up of an 

 area through subsidence or formation of some other kind of barrier; upon a close 

 investigation it has been shown in many instances that slightly different forms 

 within the original population happened to become isolated and appear as ex- 

 amples of true vicarism. 



Joiiow (/JO. 233) held forth that 6 species endemic in Masatierra correspond 

 to 6 other species endemic in Masafuera, but he did not use the term vicarious. 



