CH. XXII] GEOGRAPHICAL DISTRIBUTION 237 



one take the number of species per family in the British flora, 

 one finds it to increase steadily with the number of genera; there 

 are no breaks, as one would be inclined to expect. The families 



Monospccifi c Genera at th 13 end f curve 



Number of species (or size of area] 



Mixed curves, to show the close agreement of the hollow curves, whether 

 derived from families of plants grouped by sizes of genera (Compositae, 

 Hymenomycetineae, Simarubaceae), families of animals (Chrysomelidae, 

 Amphipodous Crustacea, Lizards), endemic genera grouped by sizes 

 (Islands, Brazil, New Caledonia), local floras grouped by (local) sizes of 

 genera (Ceylon, Cambridgeshire, Italy), local faunas (Birds of British 

 India, British Kcliinoderms), Tertiary fossils by sizes of genera, or 

 Endemic Compositae of the Galapagos by area. [By courtesy of the 

 Editor of Nature.] 



with one genus show an average of 2-2 species per family, those 

 with two an average of 8-3, with three of 10-7, with four of 12-3, 

 with five, six or seven genera of 15, with eight, nine, or ten of 



