178 ENDEMISM AND DISTRIBUTION: GENERA [pt. ii 



or continuous areas, one finds, for example, that in Africa there 

 are 835/1, 254/2, 136/3, 86/4, 97/5, 48/6, and so on, the largest 

 genus having 350 species. In tropical Asia one finds 445/1, 175/2, 

 90/3, 68/4, 77/5, 56/6, and so on, the largest genus having 600 

 species. In the north temperate region of the Old World one 

 finds 385/1, 135/2, 75/3, 45/4, 49/5, 29/6, and so on to 250. From 

 this one may go on to the world itself, and one finds (in the total 

 of 12,571) 4853/1, 1632/2, 921/3, and so on to 1600. All these 

 groups of figures exhibit markedly hollow curves when plotted 

 graphically. 



The various figures that have just been given for islands, 

 countries, continents, etc., show in a very distinct way that the 

 larger genera are found upon the larger and more isolated areas, 

 whether of islands or of countries on the mainland, as would be 

 expected upon the principle of Size and Space (Chapter xii). 

 Thus, while Ja\a has no endemic genus of more than two species, 

 nor Socotra of more than three, Borneo reaches five, Ncav Cale- 

 donia 15, IMadagascar 20, and the very isolated Hawaiian Islands 

 28. The largest island endemic genus, Oncostemon with 60 species, 

 is found in Madagascar and the Mascarenes, a large total area. 

 Astronia, the next largest, with 30 species, occupies large parts 

 of the Malay Archipelago and Polynesia. The largest genus con- 

 fined to New Zealand proper has only 9 species, but that con- 

 fined to New Zealand and surrounding islands (p. 66) has 20, 

 In the same way, the possible size of a genus increases with the 

 increasing size of the area, till we reach 600 species in a genus of 

 Tropical Asia, and 1600 in the world. 



All these groupings of genera, whether usually considered en- 

 demic, or not, whether confined to small areas, or found on 

 larger (even up to the whole world), show the same type of 

 arrangement, with the bulk of their number monotypic or di- 

 typic, and a tail running out to the larger genera, the tail being 

 longer the larger the size of the area dealt with. There is no 

 difference between the endemic genera and the rest. 



It is also evident that the sizes of genera are grouped in the 

 same Avay as the areas occupied by their species. Both go with 

 age ; the older the genus, the more space will it occupy, and the 

 more species will it have. Of course one must only deal with 

 groups of say ten genera, and must only compare allied forms, 

 to get results that are at all reliable and comparable. 



It is clear that the general types of relationship shown, whether 

 between endemic genera only, between genera of larger area 



