122 BOTANICAL GAZETTE | AUGUST 
portions of the bordering states, which, being mostly absent 
from south Mexico, Central America, and the Andes of Colom- 
bia, Venezuela, and Ecuador, reappear again first in Chili. 
Emphasis was laid upon the large percentage of Californian 
genera represented in Chili by identical or corresponding spe- 
cies, or even by species very distantly related, and their general 
absence in the intervening region. 
These lists by no means included all the North American 
elements in Andean or extra-tropical South America, nor did 
they indicate that some very notable cases represented the 
extension of South American elements into extra-tropical North 
America, though of course these additional phenomena of dis- 
tribution were discussed elsewhere in the Entwicklungs-geschichte, 
and it will be necessary to become familiar with them in the 
present paver. 
More accurately defined the regions chiefly concerned are as 
follows : 
1. In North America, the arid belt designated by Dr. 
Merriam? as the Lower Sonoran zone, including the Mexican 
tableland and adjacent western Texas, New Mexico, Arizona, 
Nevada, and Utah, with central, southern, and most of Lower 
California, approximately the region discussed by Professor 
Engler under “Das mexikanisches Hochland” and its north- 
ward extensions. 
2. In South America, the desert of Atacama from about 
Cobija to 27° south and the less arid district south to 34° ; the 
arid sand steppes and salt deserts of western Argentine along 
the east slope of the Andes, embracing in general from Cata- 
marca at the north, Cordoba at the east, and Mendoza south- 
ward toward the Rio Colorado and Rio Negro; the «‘ Chafar- 
Steppe” of Grisebach and ‘‘ Monte Formation” of Lorentz. 
With the above regions are also concerned the Gulf zone, 
with southern Brazil, Uruguay, and eastern Argentine ; and the 
high Andes of Colombia, Venezuela, Ecuador, Peru, and Bolivia 
3Geographical distribution of plants and animals, Year Book Dep. Agric. 1894+ 
207 (and note). 
