May 3i, 1924 Cell Sap Density and Environmental Conditions 
851 
pressure applied again until as much as possible of the sap was expressed. It 
was found essential to subject all samples to the same uniform thorough pressing 
because the last sap obtained from a sample is more concentrated than that which 
is obtained at first. 10 
ENVIRONMENTAL CONDITIONS 
The salient physiographic and geologic features of the central Wasatch region 
have been well described by Butler and Loughlin (15). It is an area of strong 
relief, extending from an elevation of approximately 5,000 feet at the western 
base of the range to altitudes of almost 11,500 feet on the highest summits. 
Many of the slopes are steep and include areas of bare, polished rock. The 
canyons are U-shaped, the branch canyons being of the “hanging” type and 
the heads of canyons have the basin or cirque form characteristic of recent 
glaciation. The important rocks of the region consist of quartz diorite, Cam¬ 
brian limestone, quartzite and shale which decompose into sandy to gravelly 
loam or silt loam soils. 
The topography of the Wasatch Plateau in the vicinity of Ephraim Canyon 
is much less rugged than that farther north, due mainly to the fact that the 
sedimentary sandstones and limestones interbedded with geological clay com¬ 
prise the greater part of the geological formations. The top of the mountain 
range is often quite flat and a mile or more in width. The soil is, for the most 
part, a heavy, highly calcareous clay loam or clay. 
The salient vegetational features of the main Rocky Mountain region have 
been very well described by a number of writers, among whom may be mentioned 
Bates ( 8, 4), Pearson (99), Ramaley (104, 105), Robbins (108), Rydberg (110), 
and particularly Sampson (118, 114), who has studied extensively the ecological 
relations of the vegetation of the Wasatch Mountains. There are, however, 
some major vegetational differences between the Wasatch Mountains and the 
central and southern Rocky Mountains. Pinon pine (Pinus edulis) drops out 
of the pinon-juniper type in north central Utah, leaving Utah juniper (Juniperus 
utahensis) the dominant species of the type. Western yellow pine (Pinus ponde~ 
rosa scopulorum) is found very infrequently in the northern part of the Wasatch 
Range occurring either upon the limited areas of sandy or gravelly soils or near 
streams where soil moisture conditions are exceptionally good. In Big Cotton¬ 
wood Canyon western yellow pine occurs naturally on only one site—a gravelly 
talus slope having a steep southern aspect. 
Another striking contrast between the Wasatch Mountains and the Rockies 
lies in the greater abundance of aspen (Populus tremuloides) in the Utah aspen- 
fir type, where it frequently forms pure stands on old burns. This temporary 
type of aspen may be considered a retrogression in the succession of forest types 
due to fire. Lodgepole pine (Pinus contorta) is less prominent in Utah, disap¬ 
pearing entirely south of the headwaters of the Provo River on the Uinta National 
Forest. 
Considerable variation in composition is apparent within the same type in 
different localities, evidently due principally to factors in the environment and 
to disturbances in the natural succession. For example, a pure stand of Douglas 
fir, after being burned over, may be followed by a more or less temporary stand 
of aspen—a retrogression to a sub-climax stage in the developmental succession. 
However, the aspen will be gradually and eventually wholly supplanted by the 
Douglas fir. In Taylor Canyon at present there is little aspen on the potential 
aspen-fir sites, while it is abundant in this type in Big Cottonwood Canyon* 
Another notable contrast between the forest types on these two watersheds is 
This has been reported also by Gortner. Lawrence, and Harris ( 42 ) and by Knudson and Ginsberg (71) * 
