312 APPENDIX. 



remarkable manner ; and the endemic element is specific rather than generic *. The 

 diversified oak-forests laden with epiphytical orchids, Bromeliacese, and other plants 

 equally characteristic of the vegetation south of the Isthmus of Panama afford the best 

 illustration of the correctness of this statement. It is true the oak type is not 

 peculiarly characteristic of a moist climate ; but it is essentially northern, and although 

 it has reached the Andes of South America, its development there is quite insignificant f. 

 On the other hand, the orchids associated with the oaks of Mexico belong almost wholly 

 to genera equally or more strongly represented in South America. Thus only nine out of 

 upwards of a hundred genera are endemic in our central province ; and only fourteen are 

 restricted to the country north of the Isthmus of Panama. Further, ten of the fourteen 

 endemic genera are monotypes, and the others number very few species ; moreover it is 

 noteworthy that nearly as many of the genera reach eastern as western South America. 

 Details of the distribution of this highly characteristic order in South Mexico will be 

 found on pages 267 to 271, but we do not there distinguish between the eastern and 

 western extensions in South America. From elaborate tables compiled on a slightly 

 different basis from our present, before the publication of the OrchideaB in Bentham 

 and Hooker's ' Genera Plantarum,' it appears that sixty-five of our genera also occur in 

 eastern South America, sixty-nine in western, and fifty-nine in the West Indies ; and of 

 species seventy-nine are common to the West Indies, seventy-five to Colombia, twenty- 

 two to Peru, forty-five to Guiana, and thirty-six to Brazil. On the other hand, 520 

 species of orchids are endemic in the combined areas of South Mexico and Guatemala. 

 The distribution of the Bromeliacea?, Aroideee, and Gesneracea? is very similar; and if 

 other instances of their eastern North-American associates in South Mexico are wanted 

 we may refer to the list of deciduous trees on page 309. 



The flora of Guatemala is essentially of the same composition as that of South 

 Mexico, though apparently less rich in specific diversity. About 1600 species of 

 vascular plants belonging to 677 genera are recorded from this area. Of the eastern 

 North- American deciduous arboreous types in South Mexico just alluded to, some, as 

 Tilia and Ulmus, are not known to reach Guatemala, while others, such as Liquidambar, 

 Morus, Ostrya, and Carjpinus, are present, and the two latter have here their southern 

 limit. As might be expected, too, some characteristic South-American types find their 

 northern limit in Guatemala. Noteworthy among these are the Vochysiacese ; the 

 genera Vochysia and Trigonia being both represented. 



* The phanerogamic generic endemic element consists of 198 genera for the whole of Mexico and Central 

 America, or 11 per cent, of the total ; and the Compositse, which are represented by very nearly double the 

 number of genera of any other order, and by 5 per cent, more species than the next in numerical sequence, 

 contribute forty-five of them, or 23 per cent., which is nearly twice the proportional amount of the orders 

 collectively, for only 12 per cent, of the total genera belong to the Composite. Taking North Mexico alone, 

 the proportional generic endemic element would be even higher in this order, and extending the area to 

 Texas, New Mexico, and Arizona, itwould be enormously increased ; and this applies to the generic endemic 

 element generally, confirming the view that this region constitutes a distinct plant province. 



f Particulars of this will be found at p. 261. 



