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22 BOTANY OF THE DEATH VALLEY EXPEDITION. 



Some of these species, as Acamptopappus splmroeephalus, Aster 

 mohavcmis, and Yucca arborescent, are confined to the upper altitudes 

 of the zone; while others mchsAFranseria dumosa, Hymcnoelea salsola, 

 Larrea tridentata, and Lycium andersonii are common nearly throughout 

 it. Atriplex hymenelytra grows only on gravelly mesas in conspicuously 

 alkaline soil. Cassia armata grows preferably in sandy, dry washes. 



The common perennials of the mesas are Cladothrix oblongifolia, 

 Euphorbia polycarpa, Lepidium fremontii, and Mirabilis Iceris, while 

 the most abundant of the large number of annuals are Atrichoscrispla- 

 typhylla, Ghorizanthe rigida 7 Cleometta obtusifolia, Fmcelia eriocephala, 

 Eschscholtzia minutiflora, Giliafloccosa, Leptosyne bigelovii, Plantago 

 patagonica gnaphaloides, and Sisymbrium canescens. 



Ascending from the mesa into the caiions and up broken rocky slopes 

 of the mountain ranges, one encounters certain plants that are confined 

 to these habitats. Among shrubs of this character may be designated 

 Aplopappus cuneatus,Bigelovia teretifolia, Goleosanthus atractyloidcs, and 

 Hofmeisteria pluriseta; among perennials, Arenaria macradenia, JEu- 

 cnide urens y and Nicotiana trigonophylla; and among annuals, Macrocalyx 

 micranthus, Parietaria debilis, and Pterostegia drymarioides. The plants 

 that occupy the bottoms of canons, growing upon the gravelly or sandy 

 washes which they contain, are, in the absence of running streams, 

 the species of similar situations in the open desert; but the plants enu- 

 merated above are those which grow in the shade of rocks or in their 

 crevices. Such plants are called rupestrine. Their habitat furnishes 

 them peculiar advantageous conditions, consisting of increased moisture, 

 more uniform soil temperature, «.nd apparently certain qualities of soil 

 mechanique not yet explainable. Rupestine plants present in their 

 environment and characteristics some of the phenomena of moist- soil 

 vegetation and constitute in a measure a group intermediate in these 

 respects between xerophilous and paludose plants. 



In the bottoms of many closed valleys there exist areas over which, 

 after a heavy rainfall, standing water accumulates. In the smaller 

 valleys, from which the water is soon evaporated, the resultant soil 

 formation is a level expanse of very hard clay, which in most cases does 

 not crack when dry and which is often strongly alkaline, not suffi- 

 ciently so, however, to present an efflorescence. Such an area is com- 

 monly known as a dry lake. If the valley is large and adjacent to high 

 mountains, the water which collects in it may be sufficient to keep the 

 valley-bottom moist throughout the year. In these instances the sur- 

 face of the soil, when not covered with water, is incrusted with salt or 

 some alkaline deposit. Such an area is commonly called a marsh or 

 flat, with some word like salt, soda, or alkali prefixed to indicate the 

 popular notion of the nature of the deposit, 



A dry lake contains no vegetation except at its margin. Here is 

 found a growth of shrubs consisting commonly of Atriplex polycarpa, 

 and often of A. confcrtifolia and Sutvda suffrutescens in addition. 





