190 THE MONOTYPIC GENERA [pt. ii 



type of distribution shown in minute detail; and working upon 

 large numbers, one gets it shown quite clearly. 



One may, however, go further than merely splitting up the 

 world into continents. If one take the genera endemic to South 

 America, and divide these up among the countries to which the 

 bulk of them are confined, and then take, for example, Brazil, 

 one finds that it contains G-8 per cent, of the world's monotypes 

 (genera of one species), but only 5-5 per cent, of the ditypes, 

 3-5 per cent, of the tritypes, 0-7 per cent, of the genera with ten 

 species, and so on. The other countries of South America show 

 similar, but not quite so regular, results (on account of the smaller 

 numbers). Individual islands, when they ha^'e sufficient endemic 

 genera, also show the same. Thus Madagascar contains 3-9 per 

 cent, of the world's monotypes, 2-2 per cent, of the ditypes, and 

 1 per cent, of the tritypes, the numbers afterwards becoming 

 irregular on account of their insignificant totals, but none of 

 them approaching the figure for the ditypes (the highest is 

 1-4 per cent.). 



If now, returning to the table, one look at the figures for the 

 largest area (New and Old AVorlds), which includes in general 

 genera that occur throughout the north temperate zone, the 

 tropics, or the world, but also includes a number that are only 

 found in eastern Asia and in North America {i.e. really quite a 

 small area), one finds the figiu'cs to go in the reverse direction, 

 from 1-3 per cent, of monotypes to 73 per cent, of the large 

 genera. This agrees absolutely with what has been said above 

 under Size and Space; the surprising feature is that the figures 

 increase regularly. 



If now one take the Palaeotropical region (tropical Asia and 

 Africa, North Australia, Polynesia), one finds the proportions to 

 increase up to about genera of 50 species, and regularly, and 

 then to diminish regularly. Tropical America behaves in the 

 same wa}^ but the decrease begins sooner. In other words, 

 genera of larger size tend to occur in both Old and New World 

 tropics. In tropical Asia, a much smaller area, the falling-off 

 begins much sooner, and so it does in Australia. In the north 

 temperate regions of the Old World it does not begin till about 

 the size of 50 species (the flora, however, is more herbaceous). 



There are many very interesting points to be made out from 

 the study of such statistics as these, and still more interesting 

 features can be discovered by breaking them up, and studying 

 individual regions, and families, or types of vegetation, in detail. 



