SUMMAET AM) ANALYSIS OF THE ELOKA. 211 



The numbers and percentages of the endemic and non-endemic genera, together with 

 their proportional distribution is given below. The second Table exhibits the generic 

 extension to other parts of America in the left-hand section, and countries beyond 

 America in the right-hand section. Those genera included in the column headed 

 " widely " are not repeated in any of the other columns to the right. That is to say, 

 of the 292 polypetalous genera which extend beyond America, 218 are widely diffused, 

 leaving seventy-four that extend to one, or rarely two, of the other countries or regions 

 named in the Table. 



Percentages of the Endemic Generic Element. 



Out of a total of 1849 genera of vascular plants in Mexico and Central America, 

 only 199, or about 10*8 per cent., are endemic, which is very low as compared with 

 extra-tropical South Africa and Australia, the only large countries of which there are 

 available data. Even taking Mexico alone, which is generally regarded as having a 

 highly specialized flora, the endemic genera do not amount to 12 per cent. Going 

 still farther, and including those genera common to Mexico and western North 

 America only, the majority of which may legitimately be reckoned as forming part of 

 the same floral region, in the same sense that the proportions for the whole of Australia 

 and the whole of extra-tropical South Africa are used in comparison, the percentage 

 would probably not exceed 20. Engler*, to whom we are indebted for particulars con- 

 cerning the genera of Australia, makes the total of vascular plants 1393, as he takes a 

 more restricted view than Mueller, and one more in accord with Bentham and Hooker's 

 'Genera Plantarum;' and 425 of them, or 30'5 per cent, are endemic, being nearly 

 three times as high as in Mexico. In extra-tropical South Africa the proportion is 

 even higher. Bolusf estimates the total number of genera of flowering-plants at 1255, 

 and the endemic at 446, which is equal to 35'5 per cent. Taken separately the flora of 

 West Australia would afford similar results, if not a still higher proportion of endemic 

 genera. The proportional distribution of the endemic genera is as here given : — 



Number, Percentages, and Distribution of the Endemic Genera of 



Phanerogamic Plants. 



Total endemic . ... 198 11-0 per cent, of 1794, total number. 



Endemic in north area . 

 „ in south area . 

 „ in combined areas. 



198 100-0 



* Yersuch einer Entwickelungsgeschichte der extratropischen Elorengebiete der siidlichen Hemisphere, 

 P- 34 - t < Sketch of the Elora of South Africa,' p 2. 



biol. cente.-amer., Bot. Vol. IV., August 1887. 2/ 



159 



80-3 per cent, of 198, total endemic. 



13 



" ^ '» 5» )» » >) 



26 



1 3-1 



