452 SCIENCE PROGRESS. 



is accorded, and not by all botanists. I shall have occasion 

 to refer to the affinities of this natural order in a succeeding 

 paragraph. As a matter of fact, however, it has less 

 decided distinctive characters than some of the aberrant 

 endemic genera of Madagascar ; and it does not rank with 

 such orders as the American Bromeliaceae, Sarraceniaceae 

 and Calycereae ; or the South African Bruniacese and 

 Penaeaceae, and the Australian Tremandreae. At most, it 

 ranks no higher than the least specialized of the natural 

 orders named. 



Bearing on this question, the restricted area of natural 

 orders, it is singular that no natural order is confined to 

 Asia, but there are several— Dipterocarpeae, Moringeae and 

 Salvadoraceae — which are common to Asia and Africa; and 

 the two latter are represented in Madagascar. It is true 

 that if the genera Ancistrocladus and Lophira be excluded 

 from the Dipterocarpeae, only one species of this order 

 inhabits Africa against large numbers in Asia. 



The number of genera then (1889) known to inhabit 

 Madagascar was 970, and is now probably not less than 

 1000. Bentham and Hooker (24) describe less than 7600 

 genera, but the discoveries since the publication of the 

 various parts of that work would probably bring the total 

 up to 9000 upon the broad lines laid down by them. My 

 estimate of the number of genera of vascular plants known 

 to inhabit Mexico and Central America in 1888 was 1849, 

 whereof 1794 were phanerogams. My estimate of the 

 number of phanerogamic genera in the flora of British 

 India was 2271 ; and Sir F. von Mueller's census of 

 Australian plants gave 1409 genera, including 45 genera of 

 vascular cryptogams. These figures indicate that a large 

 proportion of the genera of vascular plants must have a 

 wide range, and the approximate percentages of endemic 

 genera in each of these regions will give an idea of their 

 relative degrees of concentration in large insular and large 

 continental areas. 



In Madagascar 15 per cent, of the genera are endemic ; 

 in Central America (including Mexico), 11 per cent.; in 

 British India, 13-8 per cent.; in Australia, 30*5 per cent.; 



