THE TULAROSA DESERT 7 



presence of a grama grass {Bouteloud) forming almost a turf, and 

 by frequent clumps of an Ephedra^ of a grayish purple color at 

 this season and with 3-scaled nodes (Plate V). These bottoms usually 

 show no sign of moisture, but in two places we found water holes, the 

 water so alkaline that the horses would not drink it at the end of their 

 first day's drive. About both holes occurred salt grass (^Distichlis 

 spicata) and wire grass {Jtmcus balticus)^ both of them character- 

 istic of moist alkaline soils (Plate VI). 



In addition to their woody vegetation the White Sands appear to 

 have an abundant herbaceous vegetation which would well repay care- 

 ful systematic and ecological study. The area they cover is large, 

 probably 400 square miles or more, the physical and chemical proper- 

 ties of the soil are very unusual, and no botanist has yet thoroughly 

 studied the vegetation. 



The relation of Yucca radiosa to the sand dunes is unusually inter- 

 esting. A group of four small yucca plants standing about three feet 

 high to the tip of the highest leaf, was found upon the summit ridge of 

 a thirty-foot dune. We dug the trunk out to a depth of 14 feet. All 

 four plants were from branches of the same trunk, the lowest branch 

 arising about 16 feet from the base of the dune ; the main trunk and the 

 branches bore marks of rosettes of leaves at intervals all the way to 

 the lowest point reached. The trunk was thicker here, about 4 inches, 

 than at any point above. The strata in the cut showed that the yucca 

 once stood on the front slope of the dune. The trunk sloped in the 

 direction in which the dune was moving. In the plain in front of the 

 dunes were occasional low plants of the same species of yucca. Con- 

 sidering all the evidence the conclusion is irresistible that the yucca 

 originally grew on the plain, was engulfed by the sand, and gradually 

 grew through each successive layer of sand that drifted over it, until 

 the summit of the dune was reached. In the vicinity, at the rear of 

 the dune, were other long trunks partly denuded by the passing of 

 the dune (Plate VII) . 



A gentleman, familiar with the White Sands for twenty years, told 

 us that in that time they had advanced eastward at one point, the one 

 of greatest activity, about half a mile. A road traversing the plain in a 

 north-south direction close to the eastern front of the sand showed fre- 

 quent changes necessitated by the advance of the dune (Plate VIII). 



A section from the base of the Sacramento mountains southwest 

 through Alamogordo into the White Sands, shows four belts : ( i ) the 

 delta slopes from the mountain canyons, characterized by a nearly pure 

 growth of creosote bush (^Covillea tridciitata)^ the soil usually grav- 



