62 



THE WORLD OF LIFE 



CHAP. 



together will give more than the actual number of species in 

 the combined flora, because an unknown portion of the 

 species will be found in two or three of these divisions. 

 But he gives the total numbers for these three states and 

 also for the remainder of the nine areas. He also gives the 

 numbers which are " endemic " in these two groups of areas 

 separately and in the whole flora ; I have therefore been 

 able to ascertain the proportion which the endemic bear to 

 the total in Mexico and Guatemala, which I find to be as 

 3 to 4 very nearly, so that by deducting one -fourth of 

 the sum of the species in these areas I obtain the number 

 existing in the combined area. But as it is known that in 

 the tropics species have a less range than in the temperate 

 zone, I deduct one- fifth in the case of the three tropical 

 areas, which will, I believe, approach very nearly to the 

 actual number of species in the combined floras as given in 

 the following table : — 



Nicaragua, Costa Rica, and Panama (3000 species) 



1. Orchideae . 



2. Compositae 



3. Leguminosae 



4. Rubiacese . 



5. Gramineae 



6. Euphorbiaceae 

 Ferns 



This table brings out clearly the extra-tropical character 

 of Mexico as compared with these tropical sections of Central 

 America. No less than five orders of the former twelve have 

 to be omitted (Cactaceae, Labiatae, Solanaceae, Piperaceae, 

 and Malvaceae), which are replaced by the more exclusively 

 tropical Gesneraceae, Melastomaceae, Urticaceae, Aroideae, and 

 Palmae. Here, in two adjacent areas differing about 12° in 

 mean latitude, there is a more pronounced difference in the 

 prevalent orders of plants than exists between two great 

 regions on opposite sides of the globe. Another character- 

 istic tropical feature is seen in the large number of ferns, 

 which are nearly one-half those of the whole number found 

 in Mexico and Central America, which has an area nine times 

 as great. 



Of the other tropical American floras little need be said. 



