Histological Studies in the Artemisia Formation 7 
2 dem. and even with Artemisia tridentata itself the absorbing 
area was reached at a depth of one meter. 
In determining the vertical distribution of moisture, soil sam-: 
ples were taken at depths of 2, 4, 8, and 10 dem. In taking the 
deeper samples a pickax was used with the geotome, since only 
a 2 dem. geotome was available. Whenever leaf material was 
taken soil water determinations were made from the absorbing 
area of the plant concerned in so far as was possible. In doing 
this for Artemisia tridentata the whole plant was first broken 
down and grubbed out. Because of the weakness of the trunk 
and roots this task was easily accomplished. Then the pickax 
and hands were used to excavate to about one meter below the 
surface where the geotome was driven down for the final soil 
sample. This was a comparatively easy task in the fine sandy 
soils, but in the rocky soils of the north it was more difficult to 
obtain a sample from the absorbing area of the larger shrubs. 
The vertical distribution of water-content showed a much wider 
range of variation in the rocky soils than in the even textured 
sandy soil. 
In a recent number of the Plant World which came to hand as 
this paper was being written, MacDougal states that in his studies 
of desert vegetation he has found the same comparative uniform- 
ity in the vertical distribution of soil moisture. Because of this 
uniformity the root systems of the plants inhabiting such places 
exhibit a broad lateral development with a corresponding decrease 
in vertical range. The stratification habit of roots such as Mac- 
Dougal mentions was not noted for the plants of this formation, 
probably because in most cases the individuals were so widely 
distributed that competition between the root systems of contig- 
uous plants was reduced to a minimum. 
In the matter of climatic conditions the region covered is arid. 
There is a great diurnal range in temperature for each locality. 
At Hot Sulphur Springs at an altitude of 2,600 m. (7,800 ft.) 
frost occurred on one or two nights during the latter part of July. 
But at noon or between noon and 3:00 P.M. a temperature of 
40° C. was recorded in the Artemisia formation surrounding the 
village. The nights were not so cold in the south, but the days 
417 
