Age and area; a study in geographical distribution and origin of species . seas were taken. The averagenumber of species per genus is also not unequal (islands1582/3461, average 2-1; Brazil 533/1291, average 2-4). The endemics of mountains are also as a rule small genera,though there are a fair number of exceptions to this, but onlyin the large mountain chains. In the Andes, for example, thereare Chaetanthera (30 species), Cinchona (40), Cristaria (30), Nas-sauvia (50), Psammisia (35), Puya (25), and many more ofsmaller size. One may go on to deal with still larger floras, and find thatthey ar
Age and area; a study in geographical distribution and origin of species . seas were taken. The averagenumber of species per genus is also not unequal (islands1582/3461, average 2-1; Brazil 533/1291, average 2-4). The endemics of mountains are also as a rule small genera,though there are a fair number of exceptions to this, but onlyin the large mountain chains. In the Andes, for example, thereare Chaetanthera (30 species), Cinchona (40), Cristaria (30), Nas-sauvia (50), Psammisia (35), Puya (25), and many more ofsmaller size. One may go on to deal with still larger floras, and find thatthey are arranged in precisely the same way, so that the pheno-mena shown by the endemic genera are exactly paralleled bythose shown by genera that occupy more area. If one take (asusual from my Dictionary, in which uncertain fours are countedas fives, etc.) the genera that are confined to single continents ch. xvi] ENDEMISM AND DISTRIBUTION: GENERA 177 r/ X u (0 -IN Xc E MDLMICS. Geneva, grouped by £> cvjri/e is 5 squiresdiagonal 1^ abcwe the last. ooX J oO O U. Number of 6petie&. Curves showing the numbers of genera of one, two, three, five, ten (andsometimes more) species, in various groups of endemic genera. Alwaysthere is a great preponderance of ones and twos and a tail of few largergenera. The monotypes are at the left-hand end of the curves (1). 12 178 ENDEMISM AND DISTRIBUTION: GENERA [pt. ii or continuous areas, one finds, for example, that in Africa thereare 835/1, 254/2, 136 3, 86 4. 97 5, 48 6. and so on, the largestgenus having 350 species. In tropical Asia one finds 445/1, 175 3. 68 4. 77/5. 56/6, and so on. the largest genus having 600species. In the north temperate region of the Old World onefinds 385/1, 135/2, 75 3. 45 4. 49 5. 29 6, and so on to 250. Fromthis one may go on to the world itself, and one finds (in the totalof 12,571) 4853/1, 1632/2, 921/3, and so on to 1600. All thesegroups of figures exhibit markedly hollow curves when plottedg
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