Trans. N. V. Ac. Scz. 92 Feb. 12, 



low lands, in certain localities over thousands of acres, are thickly set 

 with mesquite, {Prozopis glandulosa), here a strong spreading shrub, 

 never a tree, but with roots disproportionately large, composed of very 

 dense tissue and furnishing a large amount of excellent fuel. Along 

 the arroyos, cottonwood may occasionally be seen, either the narrow 

 or the broad-leaved forms, {Popidus monolifera or P. angustifolid), 

 and more commonly the hacksberry, {Celtis occidentalis), and the nogal, 

 the little black walnut {/u^iatts rupestris), the Mexican Buckeye 

 {Ung7iadia speciosa), and the Guyacon {Guyacum Coulteri), The 

 dryer portions, especially the gravel terraces bordering the Rio Grande, 

 are frequently covered with the creosote plant, {Larrea Mexicana) 

 and Tonquieria splendens. 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 which the bases 

 are in contact. Usually it is without leaves, and seems as though 

 dead, but, for a brief interval 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 " chapparal " or thickets, the 

 Holacatitha is the most conspicuous, and Salizaria the most inter- 

 esting. 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 per- 

 forms the functions of leaves, and, in the spring, these bear bunches of 

 yellow flowers similar to those of Berberis. The Salizaria is a labiate 

 allied to Scutillaria, and the seed is enclosed in a balloon-like capsule, 

 similar to that of the balloon vine {Cardioz permum), also found 

 here and having the same function, namely, dissemination by the wind. 

 Two species of Acacia and one of Berberis, {B. trifoliata) all spiry, 

 help to make the chapparal as nearly impenetrable as the thickets of 

 cactus further west. 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 

 most common, one species growing in a mass ten feet or more in 

 height, with each leaf-like subdivision of the stem a foot m 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, half 

 eaten, and the flattened stems notched by their semi-circular bites. 

 One species or variety of Opuntia, growing abundantly in Chihuahua, is 

 of a deep purple color, which makes it conspicuous and often ornamen- 

 tal. 



The most striking feature in the botany of this region is formed by 

 the century plant and its allies : other species of Agave, Habranihus , 



