TEOPICAL FLORAS 65 



farther south into the uphuuls of (liiateinala, so that we only 

 get a wholly tropical flora in the small southern section of the 

 area from Kicaragua to Panama. 



The following table of the twelve largest orders in the whole 

 flora Avill be of interest to compare with that of British India; 



Mexico and Central America (11,688 species) 



1. Compositse 1518 



2. Leguminosae 944 



3. Orchidese 938 



4. Gramineae 520 



5. Cactaceae 500 



6. Rubiaceae 385 



7. Eiiphorbiacese 368 



8. Labiata? 250 



9. Solanaceae 230 



10. Cyperaceae 218 



1 1. Piperaeese 214 



12. Malvaceae 182 



Ferns 545 



The most remarkable feature in this table is the great pre- 

 ponderance of Compositse characteristic of all the temperate 

 and alpine floras of America, and the presence of Cactaceae, 

 Solanaceae, Piperaeese, and Malvaceae among the 12 predomi- 

 nant orders, the first of the four being confined to America. 



It may be noted that of the 12 most abundant orders 8 are 

 the same in these two very widely separated parts of the earth. 

 But even this table greatly exaggerates the actual difference 

 between the two very distinct floras. There are 175 natural 

 orders in British India, and of these only 20 are absent from 

 the Mexican region. Of these 20 orders 18 have less than 10 

 species (5 of them having only 1 species), so that, judging 

 from the great types of plants, the difference is wonderfully 

 small. We can therefore understand Sir Joseph Hooker's 

 view, that there are only two primary geographical divisions of 

 the vegetable kingdom, a tropical and a temperate region. 



It must be remembered, however, that even when the series 

 of orders in two remote areas are nearlv identical, there mav 

 be a very marked difference between their floras. Orders that 

 are very abundant in one area may be very scarce in the other ; 

 and even when several orders are almost equally abundant in 

 both, the tribes and genera may be so distinct in form and 

 structure as to give a very marked character to the flora in 



