C. H. TYLER TOWNSEND-BIO-GEOGRAPHY OF TEXAS. 
75 
reach highest perfection. Bananas and plantains grow, but do not fruit 
well. Tobacco attains best quality for manufacture of smoking and plug 
brands (as with Virginia tobacco of the corresponding eastern region). 
On the north the limit of the date palm and the limit of the Lower 
Sonoran zone are nearly or quite identical. 
(7) Tropical Zone. Here grow the mangrove, mahogany, royal palm, 
(Oreodoxa regia), orchids, and hosts of brilliantly-flowering trees, plants 
and shrubs, forming a luxuriant vegetation, such as is only to be found 
in a low, moist, and very warm country, which frost never reaches. 
The cocoanut palm, banana, mango, guava, pineapple, sapote, papaw, 
custard apple, etc., attain highest perfection. The date palm, sugar 
cane, orange, etc., grow well. Coffee attains highest perfection at 2000 
to 4000 feet above sea. Tobacco attains best quality for manufacture of 
cigars (as witness the Vera Cruz and Havana tobacco). The northern 
limit of the cocoanut palm and the northern sea-coast limit of the Trop¬ 
ical zone are identical. 
It has already been hinted that some of the above native desert plants 
named as characteristic of the Upper and Lower Sonoran vary locally 
somewhat in their distribution. The data under these heads must be 
taken as a whole, and in a general way. For instance, as conclusively 
shown by Dr. Merriam’s admirable work, the Mohave Desert region, 
although covered with Larrea tridentata , is to be considered as Lower 
Sonoran. In New Mexico, and south on the Mexican plateau, Larrea 
tridentata is characteristic of lower levels of the Upper Sonoran. In the 
region around the Mohave Desert, Dr. Merriam has made full investiga¬ 
tions of the limits of the tree yucca, Y. arborescens , showing, as he points 
out, that this plant there marks the upper limit of the Lower Sonoran. 
It also invades the Upper Sonoran more or less, and is even in places 
found in company with junipers, which latter suggests that either the 
Upper Sonoran fades out in such places, or the. juniper has a different 
distribution from that shown in New Mexico and invades the Upper 
Sonoran from above. Such local intricacies, variances, and disturbing 
elements of distribution need careful study over the whole country, be¬ 
fore their meaning can be made out. They will be found largely de¬ 
pendent upon meteorologic and soil conditions, no doubt. 
I will now apply the above and other data to the elucidation in detail 
of the boundaries and outlying portions of these life areas in the region 
mentioned in the title, beginning at the north. 
TRANSITION AND BOREAL. 
New Mexico and Arizona.— Rio Grande Valley to Continental Divide 
of New Mexico and Grand Canon of the Colorado. In the summer of 
1892, I made a trip .across the country from Las Cruces, in the Mesilla 
