10] 
The University of New Mexico 
Shreve and Shelford have an article “Descriptive List of 
Middle American Biota,” 77-80, which briefly outlines nine 
areas for our region: Arid Deciduous Forest (southern Sina¬ 
loa), Extreme Desert, Desert, Succulent Desert (all three in 
Sonora and Chihuahua, but separated by coniferous for¬ 
ests) Dry Grassland (Chihuahua and Durango), Desert 
Coniferous Forest, Arid Coniferous Forest, Moist Conifer¬ 
ous Forest, and High Mountain Forest (in the Sierra Madre 
Occidental, progressing from Desert to High Mountain 
Forest with increase in elevation and decrease in latitude.) 
This article is illustrated with octavo page map of Mexico 
and Central America. The symposium also contains an 
article on “Natural Areas and Regions of Mexico,” 574-596, 
by Nelson and Goldman. These writers recognize an Arid 
Lower Tropical division in Sinaloa, Covillea Association 
in much of Durango, Chihuahua, and coastal Sonora, Pinon- 
Juniper Association flanking the Sierra Madre Occidental 
above the Covillea Association, and Pine Association • over 
most of the Sierra Madre Occidental. An octavo page veg¬ 
etation map of Mexico accompanies the above article, but it 
contains several gross errors. This same map was used to 
illustrate “The Natural Regions of Mexico,” by E. M. San¬ 
ders in Geographical Review , 11:212-226, 1921. La Vege¬ 
tation de Mexico , 1899, by Jose Ramirez, contributes little 
of value, as it lacks a vegetation map and is composed 
mainly of translations from foreign botanists such as Grise- 
bach, Hemsley, and Fournier. 
Several plant geographies devote small sections to 
northwestern Mexico. These general works only confuse 
the subject by adding new terms to an already cluttered 
terminology, and the maps are on too small a scale to be of 
much practical value. Among the best of these works are: 
Rubel, Eduard. Pflanzengesellschafen der Erde, 1930, with a 
map by H. Brockmann-Jerosch. 
Graebner, Paul. Lehrbuch der allgemeinen Pflanzengeo- 
graphie, 1929. 
Braun-Blanquet, J. Pflanzensoziologie , 1928. 
