LIST OFePi ares, 
BEATE Lai feel ce is wives AST Wi wis Se eet at oe 0 eR ane tel eee ce 
The Tumamoc Hills from the South. Tumamoc Hill, on which the Desert 
Laboratory stands, on the left, connected by a ridge with Sentinel Hill 
on the right. Santa Catalina Mountains in background. 
East side of Tumamoc Hill looking North; flood-plain of Santa Cruz River 
at right. In the foreground a heavy growth of Encelia farinosa, with 
other characteristic vegetation. 
PUGATE 2 od 4S eee hates oi hele soho ee atid gi nya ee eee Re gta ee eRe ee a 
Salt River at a point near Phoenix, Arizona, soon after high water. 
West side of Tumamoc Hill, looking West across the wash and adjacent 
slopes. Tucson Mountains in background. The path leads up the 
Tucson slope. 
15) OW Oke, ae ene Panam Pe OPS ERTS PoC ook ne yeh, ere ae MERC OES 
Cut bank of Santa Cruz River near Tucson, showing results of erosion. 
Roots of mesquite exposed. 
Dry bed of Santa Cruz River. Willows and cottonwoods on banks. 
PYUATE (Aso cited oo ais ot ce Sin a ne ee ee 
Edge of mesquite forest, on plain of Santa Cruz River, South of Tucson. 
Mesquite on sand-dune, Salton Basin. 
PUA TE 95 Or desis aralatae 8 sae a Ne nh os ole REGS GARE ee EE, ve ee 
Salt-spot in Salton Basin. Clumps of Allenrolfia near the center and masses 
of Atriplex nearer the margin, as seen at the left. This area, now cov- 
ered by water, was photographed before the last invasion of the Salton 
Sea. 
‘The wash Northwest of Desert Laboratory. Lining its banks are Cercrdiwm 
torreyanum, Acacia greggi, A. constricta, Prosopis velutina, and Celtis 
pallida. 
PATE “6 05 dag cice San oss 4 wep whe im 905, wo, Reidy 05) 9 fahaoigeee SRR 
Single individual of Cercidium torreyanum. Branching opuntias in back- 
ground. 
Ephedra trifurca in wash West of Desert Laboratory. 
fA 90. lg a ree Soe Cem MR ce oe. AR 
Creosote-bush a year old, showing comparative extent of top and root-system. 
Vegetation of the wash. In foreground Yucca elata. 
PLATE «BOs Som @Som vn os eon Mors an EDM ae oe ie pPONS ede nae te ota ee eS 
Zone of creosote-bush at the foot of Tumamoc Hill on the North. In the 
background Santa Catalina Mountains beyond the flood-plain of the 
Santa Cruz River. 
Tucson slope beyond the wash West of Desert Laboratory. I vanseria del- 
tordea and Opuntia fulgida constitute the characteristic vegetation at 
this point. 
PLATE: 6 ogc acu 4c ie 6h 0 la OG ok ea oop cine ee ee 
Slope of Tumamoc Hill showing a strong growth of characteristic vegetation 
in which Fouquieria splendens and Parkinsonia microphylla are con- 
spicuous. 
Right side of gulch near Laboratory, with generally south exposure. 
PLATE: 10. i505 Saisie, Hedges wi Sis eating oe ere ee ee ee ee 
Left side of gulch near Laboratory, with generally north. exposure. 
Lippia wright forming a nearly pure growth on the left side of the gulch, 
near its head. 
PLATE OUT aiysg atk. ayes aps. bs 5 nie. Sn ps satel ean ect ee es et 
Mesquite infested with mistletoe (Phoradendron calijornicum). 
Rank growth of winter annuals, at this place chiefly Amsinckia spectabilis. 
PLATE 12. Lichens on North face of rocks above Desert Laboratory.......... 
IV 
Facing 
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