123 
strong, spreading shrub, never a tree, but with roots (disproportion- 
ately large, composed of very dense tissue and furnishing a large 
amount of excellent fuel. Along the arroyos, cottonwood may occa- 
sionally be seen, either the narrow- or the broad-leaved form {^Popii- 
his monilifera or P. angustifolia)^ and more commonly the hack- 
berry {Celtis occidentalis), and the nopal, the little black walnut 
(Juglans rupestris)^ the Mexican buckeye ( Ungnadia speciosa), and 
the guayacan {Guaiacum Coulteri), The drier portions, especially 
the gravel terraces bordering the Rio Grande, are frequently covered 
with the creosote-plant {Larrea Mexicana) 2^\id Fonqinera splende?is. 
The latter forms a cluster of fifteen or twenty canes, ten or twelve 
feet high, springing from the same root and bristling with spines an 
inch or more in length, of wiiich the bases are in contact. Usually 
It is without leaves, and seems as though dead; but, for a brief inter- 
val in the rainy season, it is covered with small, crowded, obovate 
leaves, and from the summits of each stem springs one or more 
spikes of brilliant crimson flowers. 
Among the shrubs which form the *' chaparral" or thickets, the 
Holacantha is the most conspicuous, and Salazana\\\t most interest- 
ing. The former, as its name implies, is a mass of thorns, which are 
often as large and strong as those of the honey -locust. The branches 
and spines are covered with a green epidermis, which performs the 
functions of leaves, and, in the spring, these bear bunches of yellow 
flowers similar to those of Berberis. The Salazaria\% a labiate allied 
to Scutellaria^ and the seed is inclosed in a balloon-like capsule, 
similar to that of the balloon-vine {Cardiospermmn),-A%o found here, 
and having the same function, namely, dissemination by the wind. 
^ 'O species of Acacia and one of Berberis {B. trifoliata), all spiny, 
p to make the chaparral as nearly impenetrable as the thickets of 
cactus further w^est. We are here fairly within the confines of the 
cactus country, but not in its heart. Many species differing much 
in habit are constantly in sight — the '' nopal," an Opuntia, being the 
"^ost common, one species growing in a mass ten feet or more in 
[weight, with each leaf-like subdivision of the stem a foot in diameter. 
Though covered with spines, this plant is largely eaten by cattle, and 
nothing is more common than to see a patch of it trampled down, 
l^alf eaten, and the ^flattened stems notched by semicircular 
^ites. One species or variety of Opuntia, growing abundantly in 
Chihuahua, is of a deep purple color, which makes it conspicuous and 
often ornamental. 
The most striking feature in the botany of this region is formed 
l^ythe cehtury-plant and its allies, other species of Agave, Habran- 
^nus and Dasylirion, and the yuccas. In many places these are the 
hel 
otily plants attaining any large size, and are very numerous, scattered 
over the plains and slopes of the mountains; the plants notcrowded, 
put separated by intervals of a few feet, which are occupied with a 
luxuriant growth of gramma grass. The yuccas belong to four 
species, or three species and two varieties, Yuua angusttfoha and Y 
bjtccata. Of these, two rise to the height of five to hfteen feet, with 
runks from six to twelve inches in diameter, the crowded, radiating 
'eaves crowning the summit in a round or oval mass, six feet or more 
