74 
TRANSACTIONS OP THE TEXAS ACADEMY OF SCIENCE. 
(1) Arctic or Arctic-Alpine Zone. Above the limit of tree growth. 
(2) H-udsonian Zone. Characterized by forests of spruce (Picea spp.). 
In the Hudsonian Alpine zone of the mountains of Arizona and New 
Mexico, the species of spruce is Picea engelmcCnni , and there occurs mixed 
with it the fox-tail pine, Pinus aristata.. 
(3) Canadian Zone. Forests of Douglas fir, Pseudotsvga douglasii, 
interspersed with aspen, Populus tremuloides. In the Canadian Alpine 
zone of the Rocky Mountains, Pimis flexilis macrocarpa also occurs with 
the fir and aspen. White potatoes, turnips, beets, and hardy cereals do 
moderately well. 
(4) Arid Transition Zone. Characterized by Pinus ponderosa or yel¬ 
low pine above, and Pinus edulis (pinon or nut pine), and Juniperus spp. 
(juniper or so-called cedar) below. Certain oaks occur sparingly and 
locally with the 3 r ellow pine, as Quercus undulatus gambellii and other 
species; below with the pinon and cedar there occurs the more southern 
form of the mountain mahogany, Cercocarpus paroifoUus , while a some¬ 
what hardier species, C. ledifolius , is more characteristic of the yellow 
pine belt. 
The apple (Oldberg, Greening, etc.), cherry, white potato, barley, and 
oats attain highest perfection. Plums grow and fruit. 
(5) Upper Sonoran Zone. Characterized in a general way by Sarco- 
batus , Atrip lex, Dasylirion , Robinia neomexicana , Fallugia paradoxa , 
Celtis occidentalis. Quercus undulata wriglitii , and Agave heteracantha and 
parryi above; with scrub mesquite (P. juliflora), Yucca augustifolia and 
baccata, Echinocactus. Ephedra, Opuntia, Larrea tridentata, Krameria, 
Zizyphus , and Fonquiera splendens on lower mesas; and Populus fremontii 
wislizeni, Salix, Prosopis pubescens , etc., in river valleys. It must be 
stated that these data refer most particularly to the southern half of New 
Mexico, western Texas, and northern Chihuahua, and that the distribu¬ 
tion of these plants may in some cases be somewhat different in other 
places. 
Here the Ren Davis and wine-sap apples, pear; peach, apricot, quince, 
sweet potato, and grape (Concord, Catawba, Isabella, Mission, etc.), attain 
highest perfection, especially in the lower portions. Plums do exceeding 
well. Cotton will grow fairly well from seed in certain localities in the 
lower portions, as in the Mesilla valley, but it would be an uncertain 
crop at best, on account of early and late frosts. 
(6) Lower Sonoran Zone. Here we have the tree yuccas, Y. arbores- 
cens , Y. fllifera, larger specimens of Y. australis, and Y. treculeana; tree 
cacti, Opuntias of various species which attain an immense growth; and 
the mesquite (P. juliflora) attains tree-like dimensions. 
The date palm, orange, lemon, lime, olive, pomegranate, cotton, 
sugar cane, raisin grape, almond, fig, and maguey (Agave americana) 
