302 Part III. Chapter 3. 
represent the eastern rim of the Mexican table-land. Here the rainfall reaches 
its greatest total, for the clouds which pass over the chaparral region without 
depositing their moisture strike the mountains higher up and deposit their 
moisture in copious showers. This tropic forest may be considered as a northern 
extension of the forests of Tehuantepec and Central America. It sends an arm 
up the west coast, as far, as San Blas and gradually gives way to a semitropic 
forest above Tampico on the east coast, which finally loses its identity, as a 
semitropic forest in the northwestern part of the Mexican state of Nuevo Leon. 
Mountain Flora of Mexico. The high mountain flora of Mexico deserves 
more than a passing notice. Generically the alpine flora is related to that of 
the Rocky Mountains, for we find in fact a large number of northern genera 
[Draba, Viola, Potentilla, Alchemilla, Hieracium, Pedicularis, Funcus, Carex) 
scattered along the mountains of Mexico and South America south to Fuegia 
and southern Chile where between sixty and seventy northern genera occur. 
Very few of the peculiarly American, or Mexican genera reach the altitudinal 
limit of vegetation where the plants of northern and Andine derivation are 
about equally balanced, thus at 13,000 feet out of ı7 genera, ı2 are northern, 
2 endemic and 3 Andine. At 14,000 feet out of ı5 genera, ıı are northern, 
3 Andine and ı endemic. Above 14,000 feet (4267 m), the few northern plants 
are balanced by the others and at snowline Arenaria and Alchemilla are com 
fronted by the Andine Chöonolaena. The number of species common to the 
higher cordilleras and peaks of Mexico and the Rocky mountains is extremely 
small. Mexico and Central America possess a great many endemic species 
pointing to a long separation floristically speaking of the two mountain systems 
and to the fact that a connection never was established between the snow 
deposits on the Rocky mountains and those found on the higher Mexican 
summits. Specifically the high mountain flora of Mexico is related to that of 
the Andes of South America. Consequently these mountains possess a mix 
flora of northern plants; endemic ascendants from the temperate plateau base, 
most abundant in the middle levels and diminishing upwards; thirdly, southerä 
plants ascendant from the tropics, and fourthly, the Andines, such as Acaena 
Pernettya and Chionolaena r; 
Guatemalan Flora. The central, or Guatemalan region”), which includes 
Guatemala, San Salvador and Honduras comprises three elements of unequal 
development. There is the tropic element, largely consisting of the littoral belt, 
which is comparatively unimportant. The xerophilous element of the dry regions 
of the plateau, which may be considered to be an extension of the characterisie 
flora of North Mexico. This element is the dominant one in many distrietS 
Guatemala which were formerly covered with dense forests before the oCcU 
pation of the country by the agricultural Indians. CooR states that in all ae 
nuded areas on the desert plains and in regions now covered with forest; 
ı) GApDow, Hans: Altitude and Distribution of Plants in southern Mexico. Journal of the ” 
Linnean Society, Botany XXXVII: 429—440. 
2) HEMSLEY, 1. c., see p. 83, Bibliography. 
