848 
Journal of Agricultural Research 
Vol. XXVIII, No. 9 
SELECTION OF SITES 
If differences in the density of the sap are in any way correlated with site, they 
will presumably be the more pronounced the more diverse the site conditions. 
Extremely varied site conditions were available in Big Cottonwood Canyon, 
southeast of Salt Lake City, Utah. The Cottonwood Nursery of the Forest 
Service proved a suitable place for the establishment of a properly equipped base 
from which to carry on the tests. Material was collected all the way from the 
margins of streams in the sagebrush desert southeast of Salt Lake City to timber- 
line on the summit of the Wasatch Range. A supplemental collection was also 
made on the Beaver Creek watershed near the western end of the Uinta Moun¬ 
tains in connection with other work. Two winter collections were made on the 
Taylor Canyon watershed in the Wasatch Mountains east of Ogden, Utah. 
These were not limited wholly to the most typical portions of the sites which are 
discussed below, but were made as opportunity offered and subsequently classified 
with reference to site. The differences between the sites, as shown by the aver¬ 
ages in the tables which follow, might at first appear not as large as they should 
be, but it must be remembered that one site grades imperceptibly into another; 
and the transition between areas as well as the typical portions of each site should, 
therefore, furnish their quota of determinations. As a further control on this 
series of tests another was made on the Ephraim Canyon watershed extending 
from the alkali.flats on the desert west of Ephraim, Utah, to the summit of the 
Wasatch Plateau, where detailed climatic records have been secured from 1913 
to 1922 at three different elevations. 8 Many of the samples for these tests were 
collected in the immediate vicinity of the climatic stations, thus offering an 
opportunity for correlating sap density with climatological data. 
COLLECTION OF LEAF MATERIAL 
The leaves were gathered as quickly as possible, and were packed tightly in 
thick-walled test tubes of about 100 cc. capacity. Every precaution was taken 
to prevent contamination. Except when additional material was being put in, 
the tubes were kept tightly closed with rubber stoppers, to preclude loss of water 
by evaporation and consequent increase of the sap concentration. When mate¬ 
rial was collected which was still wet with rain or dew the leaves were at once 
wiped dry with some clean absorbent substance. Before placing the test tubes 
in the freezing mixture the possibility of contamination was further precluded by 
capping them with oiled paper held firmly by a strong rubber band. As soon 
as possible after collection the tubes were placed in a slushy mixture of finely 
chopped ice and salt, where a temperature of —15 °to —17° C. was maintained. 
They were later thawed out for the extraction of the sap. Although any suitable 
receptacle would serve for the freezing mixture, a double-walled water-tight 
wooden freezing box holding three to four dozen test tubes at a time proved the 
most satisfactory and efficient equipment for the purpose. Each of the two 
compartments of the freezing box was provided with a false top which had 18 
to 24 holes in it for holding the tubes firmly with their upper ends just above the 
freezing mixture. The box was covered with a lid which projected down over the 
sides for about 4 inches. With this type of portable freezing box it was possible 
to make two-day trips by automobile to remote points and return to the field 
laboratory with the samples still frozen. 
8 The writer is under particular obligation to Dr. A. W. Sampson, formerly plant ecologist, and H. E. 
Malmsten, grazing examiner, Great Basin Grazing Experiment Station, who aided very materially in the 
conduct of the control tests through actual participation in the work, and who have kindly placed sum¬ 
maries of the climatological records at the writer’s disposal in advance of their publication in a forthcoming 
bulletin of this department. Inasmuch as the detailed records are soon to be published by these investi¬ 
gators, the writer has made use of the summaries only, the most of which are shown graphically in figure 5 . 
