62 VEGETATION OF A DESERT MOUNTAIN RANGE. 
moisture for north and south slopes. For the stations at 4,000, 5,000, 
and 6,000 feet the percentages for the two slopes scarcely differ by 
more than the error which may be attributed to the inequalities of the 
moisture in adjacent bodies of soil. Nevertheless, in all but two cases 
there is a slightly greater moisture x : . 
content on the north slope than on ] 
thesouth. At7,000feet the difference 
between the two exposures becomes 
greater, and is still greater at 8,000 
and at 9,000 feet. An inspection of 
the averages (see fig. 10) shows that 
the south slope at 7,000 feet has a 
lower soil moisture than the north 
slope at 6,000 feet. The south slope 
at 8,000 feet, however, has a higher 
moisture than the north slope at 
7,000 feet. 3,000 hoo FT S000) 7000 a0 9,000 
The fact that there is a very slight Fie. 10.—Graph showing vertical increase 
difference between the soil moisture of soil moisture at 15 cm. in the Santa 
of north and south slopes at lower Ge ioe niet: 
elevations and a greater difference Average of three determinations in arid 
with increasing altitude would sug- fore-summicr, 
gest that there might be a more pronounced set of vegetational phe- 
nomena resulting from slope exposure at higher elevations than at lower 
ones. This is, indeed, the case, and will be discussed under a later 
heading (see p. 98). 
Tasie 8.—Soil moisture in the arid fore-summer and arid after-summer at a depth of 15 em. 
on north and south exposures, in shade and open, at various altitudes on the Santa Catalina 
Mountains. 
Date. Elevation. Blope. Location. | Moisture. 
exposure. 
Feet 
May 27, 1910...... 5,300 South Open ee 
Dox seaeew sex 5,300 South Shade 2.4 
DOs es:asced see 5,300 North Shade 3.8 
May 29, 1910...... 7,600 South Open, base 
of slope 4.7 
DOg 5 akan 7,600 South Open, crest 
of ridge 3.9 
May 30, 1910...... 5,030 South Open 5.7 
Sept. 24, 1910...... 4,600 South Open 22 
DO gins eeu eam 4,600 North | Open 4.0 
DO sis ieirg ceneceas 5,300 South Open 2.9 
Dong 24% axdinos 5,300 North | Shaded 2.6 
In the summer of 1910 several samples of soil were taken for the 
determination of the moisture conditions on opposed slopes and in 
shaded and open soil, as well as on the top and at the base of a slope. 
These data are shown in table 8. The September readings, when taken 
