4 DESERT BOTANICAL LABORATORY 



{Tillandsia) . Between Sabinal and Uvalde occur areas on the 

 higher, more sterile parts of the plain, over which the mesquite and 

 oaks are wanting, the undergrowth, however, remaining. These 

 areas often contain a growth of an Acacia 2 to 3 feet high with dark 

 yellowish-green persistent foliage, the whole plant suggesting the 

 creosote bush of the more western desert. 



Between Del Rio and Devils River a change in the flora takes place, 

 the sotol (^Dasylirion) becoming the most conspicuous feature of the 

 upland vegetation, with a broad leaved Tucca having a trunk i to 6 

 feet high, a shorter leaved grayer plant than the one about San Antonio. 

 The Acacia mentioned earlier and various shrubs, chiefly gray leaved 

 and spinose, are also abundant, while the mesquite is small and con- 

 fined chiefly to the ravines. A lechuguilla {Agave) occurs on rocky 

 slopes and thin soils, and a coral bean {Sophora secundijlora), with 

 its shining, bright green leaves, in the canyons. 



Between Shumla and Dorso the ocotillo {Fouquieria splendens) and 

 the creosote bush ( Covillea tridentata) appear, interspersed with 

 the large yucca, the lechuguilla growing in abundance on thin rocky 

 soils with acacia, and the mesquite and a small juniper growing in the 

 washes. The area is characterized also by a second smaller species 

 of Opuntia^ in addition to the larger one earlier mentioned, and by an 

 Ephedra^ probably E. antisyphilitica . The ocotillo disappears at 

 an elevation of about 2,000 feet as the plateau west of the Pecos is 

 reached. 



THE SAND DUNES OF CHIHUAHUA. 



South of El Paso and crossed by the old traders' trail from Santa 

 Fe to the city of Chihuahua is a long stretch of sand dunes which we 

 had determined to examine ; these were familiar to the early travelers 

 but are almost unknown to the botanists of today. Taking a Mexican 

 Central train at Juarez we were put off, through the courtesy of the 

 railroad officials, among the sand dunes, about six miles south of the 

 station of Samalayuca. This station is eighteen miles from Juarez and 

 one mile north of Los Medanos. 



The dunes where the railroad crosses them are about forty feet high, 

 with scant winter vegetation consisting of a few w^oody plants, princi- 

 pally a labiate bush {Poliomintha incana)^ an Artemisia^ a Chryso- 

 thamnus^ a Tucca {Tucca radiosa)^ and a suffrutescent Senecio. 

 Two perennial grasses, an Andropogon and a Sporobolus with a spike- 

 like panicle {Sporobolus cryptandrus) ^ are of frequent occurrence as 

 are the remnants of many annual plants. The Tucca takes an impor- 

 tant part in binding the sands ; roots were seen extending in a nearly 

 horizontal direction forty feet from the plant. 



