170 ENDEMISM AND DISTRIBUTION: GENERA [pt. ii 



what is often supposed, the proportions of endemic genera upon 

 islands are usually small : they range from nothing for the British 

 Islands to about 12-20 per cent, upon such islands as Juan 

 Fernandez, the Mascarenes, and New Caledonia, being as usual 

 larger in the more southern islands. On larger areas of grovmd 

 the proportions are greater; Brazil has about 21 per cent, of its 

 genera endemic, and so has Chile, Australia about 30 per cent.. 

 South Africa about 35 per cent. Africa as a whole has about 

 46 per cent., and the proportions increase with increasing area 

 till one finds 100 per cent, endemic in the world. 



AVhilst in general it is true that increasing size of area, greater 

 isolation, and greater nearness to the southern limit of about 

 40-48° S. are accompanied by increasing number and proportion 

 of local genera, these are probably not the only factors in the 

 question. If the country from which the invasion of plants has 

 come be inhabited by great numbers of them, or if the communi- 

 cation between them be broad, the proportion of local genera 

 will be more likely to be large. 



There is no definite and demonstrable difference between en- 

 demic genera and others, and we shall endeavour to show, just 

 as in the case of species, that the phenomena exhibited by them 

 are simply a miniature of those exhibited by genera as a whole. 



One may, to a very large extent, repeat the preceding chapter, 

 but with genus substituted for species, and family for genus, and 

 find it to agree with the facts about endemic genera, which 

 behave like the species. Just as in their case, the areas occupied 

 by genera, whether so local that they are classed as endemic, or 

 whether of larger size, are nicely graduated from small to large. 



